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Understand a key tool for optimizing an industrial process
Process gas chromatography is a method used to separate and analyze chemical compounds in an industrial process. First established in the middle of the twentieth century, it aims to return analytical results rapidly enough that they can be used to optimized a fluid processing plant. It is a complex process which demands meticulous training of process gas chromatograph engineers and operators.
Process Gas Chromatography: Advanced Design and Troubleshooting offers an essential companion volume to the author’s earlier Process Gas Chromatographs: Fundamentals, Design and Implementation. It builds on the previous volume’s foundation to offer a full understanding of how PGC technology can be optimized and applied to specific processes. Focused on advanced principles and practical methods, it’s a must-own for process engineers at any professional stage.
Process Gas Chromatography readers will also find:
- Extensive troubleshooting assistance including many test sequences for diagnosing and correcting malfunctions
- Coverage of the theory required to improve reliability and accuracy of PGC methods
- A detailed summary and self-assessment questions accompanying each standalone chapter
Process Gas Chromatography is ideal for end-user process analyzer engineers, applications chemists, maintenance personnel, and troubleshooters working in the fluid processing industries.
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Veröffentlichungsjahr: 2024
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Table of Contents
Cover
Table of Contents
Title Page
Copyright Page
Dedication Page
Contributors
Preface to the first book
Preface to the second book
Acknowledgments
1 Fundamentals
Introduction
Gas chromatography
The science of GC
The gas chromatograph
The contents
Becoming a PGC expert
Did You Get It?
References
2 Measures of perfection
Performance indicators
Chromatogram data
Calculated performance indicators
Practical aspects of theory
Using the theory
Did you get it?
References
3 Column technology
Introduction
Column types
Mechanism of retention
Packed columns for GSC
Packed columns for GLC
Packed column technology
Capillary column technology
Packed or capillary? A comparison
Did you get it?
References
4 The stationary phase
Liquid phases
Silicone liquid phases
Non‐silicone liquid phases
Waxy polymers
Column temperature effects
Choosing a liquid phase
Making a choice
Adsorption columns
Did you get it?
References
5 PGC column design
The design objective
Design strategy
Achieving resolution
A deeper understanding
Optimizing liquid phase performance
Exploring the power region
Optimizing retention factor
A worked example
Did you get it?
References
6 Optimizing performance
Caution
Optimum flow rate
Getting a fast analysis
A worked example
Designing for fast analysis
Did you get it?
References
7 Extracolumn broadening
Introduction
Sample injection
Sample size calculations
Flow path geometry
The theory
Worked examples
Sample injection
Open tubing
Did you get it?
References
8 Evaluating peak shape
Real chromatogram peaks
Normal asymmetric peaks
What causes asymmetry?
Problems with asymmetric peaks
Tailing peaks
Diagnosis of deviant peak shapes
Did you get it?
References
9 Columns in series
The need for multiple columns
History of the technique
Pressures in series columns
Example calculations
Column systems
Did you get it?
References
10 Backflush systems
Introduction
Backflush theory and practice
A worked example
Did you get it?
References
11 Heartcut systems
Origin and development
Heartcut column system
Making the cuts
Setting the valve timing
Diagnosis
Similar column systems
Did you get it?
References
12 PGC troubleshooting
Is there a problem?
Validation strategies
Troubleshooting
Evaluating the baseline
Prime suspect – the detector
Diagnosis
Did you get it?
References
13 Troubleshooting chromatograms
Reading the chromatogram
Diagnosing chromatographic faults
Key properties of peaks
Key properties of spikes
Key properties of bumps
Key properties of steps
Epilog
Did you get it?
References
Answers to self‐assessment questions
Subject index of SCI‐FILEs
Glossary of terms
Index
End User License Agreement
List of Tables
Chapter 3
Table 3.1 Subjective Evaluation of Columns Used in PGCs.
Table 3.2 Typical Tubing for Packed PGC Columns.
Table 3.3 Selected Mesh Sizes.
Table 3.4 Typical Tubing for PGC Capillary Columns.
Table 3.5 Phase Ratios of WCOT Columns.
Table 3.6 Phase Ratio and Column Performance.
Table 3.7 Optimum Flow Rates for Capillary Columns.
Table 3.8 Experimental Comparison of Packed and Capillary Columns.
Table 3.9 Comparison of PGC Column Types.
Chapter 4
Table 4.1 Vendor Codes for Columns and Liquid Phases.
Table 4.2 Typical Polarity of Solutes.
Table 4.3 Strength of Solvent–Solute Interaction.
Table 4.4 Popular Polysiloxane Liquid Phases.
Table 4.5 Popular Non‐silicone Liquid Phases.
Table 4.6 McReynolds Probes.
Table 4.7 Confirming Equivalent Liquid Phases.
Table 4.8 Selectivity of Common Liquid Phases.
Table 4.9 Typical Active Solid Stationary Phases.
Table 4.10 Typical Porous Polymer Stationary Phases.
Chapter 6
Table 6.1 Values of the
k
‐Function in Equation 6.10.
Table 6.2 Values of the
k
‐Function in Equation 6.13.
Table 6.3 Quick Reference Guide to Rate Theory.
Table 6.4 Four‐Step Optimization of Analysis Time.
Chapter 7
Table 7.1 Extracolumn Limit Parameters.
Chapter 8
Table 8.1 Troubleshooting Peak Shapes.
Chapter 9
Table 9.1 A Lexicon of GC Methods.
Table 9.2 Comparing Laboratory and Process Gas Chromatographs.
Table 9.3 Average Pressures in Identical Series Columns.
Table 9.4 Pressures and Retention Times for Columns in Series.
Chapter 10
Table 10.1 Calculation Data for Backflush Event Time.
Table 10.2 Calculation Data for Backflushed Peaks.
Chapter 12
Table 12.1 Diagnosing a Drifting Baseline.
Table 12.2 Diagnosing a Wandering Baseline.
Table 12.3 Diagnosing a Cycling Baseline.
Table 12.4 Diagnosing a Noisy Baseline.
Chapter 13
Table 13.1a Procedure for Diagnosing Peak Size Problems.
Table 13.1b Procedure for Diagnosing Peak Shape Problems.
Table 13.1c Procedure for Diagnosing Peak Separation Problems.
Table 13.2 Procedure for Diagnosing Chromatogram Spikes.
Table 13.3 Procedure for Diagnosing Chromatogram Bumps.
Table 13.4 Procedure for Diagnosing Chromatogram Steps.
List of Illustrations
Chapter 1
Figure 1.1 A Basic Gas Chromatograph.
Figure 1.2 A
Typical
PGC Chromatogram.
Chapter 2
Figure 2.1 Typical Chromatogram Measurements.
Figure 2.2 Significance of an Air Peak.
Figure 2.3 Measurements for Separation Factor.
Figure 2.4 Measurements for Resolution.
Figure 2.5 The Gaussian Peak Shape.
Figure 2.6 Spatial and Temporal Separations.
Figure 2.7 Achieving Resolution.
Figure 2.8 Measurements for Plate Number.
Chapter 3
Figure 3.1 Three Kinds of Capillary Column.
Figure 3.2 Origin of Dispersive Forces. (a) Two adjacent neutral atoms or mo...
Figure 3.3 Nonpolar and Polar Molecules.
Figure 3.4 Typical Packed Columns.
Figure 3.5 Typical PGC Capillary Columns.
Figure 3.6 The Column Performance Triangle.
Figure 3.7 Theoretical Minimum Plate Height.
Figure 3.8 A Fronting Peak.
Figure 3.9 A Tailing Peak.
Figure 3.10 (a) Sample Capacity and Column Diameter. (b) Sample Capacity and...
Chapter 4
Figure 4.1 Structure of Poly[dimethylsiloxane].
Figure 4.2 Principle of Retention Index.
Figure 4.3 Predicting Retention by McReynolds Constants.
Figure 4.4 Effect of Adsorption Isotherm on Peak Shape.
Chapter 5
Figure 5.1 Plate Number for Resolution.
Figure 5.2 Optimum Retention Factor.
Figure 5.3 The Power Region.
Figure 5.4 Challenge Question.
Figure 5.5 Peaks in Power Region.
Figure 5.6 Optimum Performance.
Chapter 6
Figure 6.1 Typical Column Efficiency Curve.
Figure 6.2 van Deemter Curve.
Figure 6.3 Effect of Slow Mass Transfer.
Figure 6.4 Advantages of Using a Longer Column.
Figure 6.5 Effect of Carrier Gas Density.
Figure 6.6 Effect of Film Thickness or Liquid Loading.
Chapter 7
Figure 7.1 An Ideal Injection Profile.
Chapter 8
Figure 8.1 Three Asymmetric Chromatogram Peaks. (a) Normal Peak. (b) Tailing...
Figure 8.2 Measuring Peak Skew.
Figure 8.3 Typical Partition Isotherm.
Figure 8.4 Isotherms and Peak Shape. (a) Normal Peak. (b) Ideal Peak. (c) Fr...
Figure 8.5 Typical Adsorption Peaks.
Figure 8.6 A Second Retention Mechanism.
Figure 8.7 The Poisson Distribution.
Figure 8.8 The EMG Peak Model.
Figure 8.9 Retention Shift with Concentration.
Figure 8.10 Effect of Peak Shape on Resolution. (a) At Low Concentration. (b...
Figure 8.11 Normal and Tailing Peaks. (a) No Peaks Tail. (b) Some Peaks Tail...
Figure 8.12 Resolution of Normal Asymmetric Peaks.
Figure 8.13 Normal Peaks at Low Resolution.
Figure 8.14 Asymmetry due to Merged Peaks. (a)
R
s
= 0.75. (b)
R
s
= 0.5.
Figure 8.15 Looking for Merged Peaks. (a) Full Chromatogram. (b) Stretched d...
Figure 8.16 Effect of Peak Size. (a) Small Peaks. (b) Large First Peak. (c) ...
Chapter 9
Figure 9.1 Dual Phase Selection Chart.
Figure 9.2 Nonlinear Pressure Drop.
Figure 9.3 Pressure Distribution in Series Columns.
Chapter 10
Figure 10.1 Ten‐port Backflush Column System.
Figure 10.2 PGC Chromatogram using Backflush to Measure.
Figure 10.3 Six‐port Backflush Column System.
Figure 10.4 Live Tee in Pass‐through Mode.
Figure 10.5 Live Tee in Backflush Mode.
Figure 10.6 A Regrouping Column System. (a) Components to be regrouped are l...
Figure 10.7 Idealized Backflush Event Setting.
Chapter 11
Figure 11.1 Large Peak Tailing Problem.The chromatogram in (a) is without he...
Figure 11.2 Heartcut Column System.
Figure 11.3 Live Tee in Vent Mode.
Figure 11.4 Live Tee in Heartcut Mode.
Figure 11.5 Single‐cut Heartcut Chromatogram.
Figure 11.6 Schematic of a Single Cut.
Figure 11.7 Single Cut for Two Analytes.
Figure 11.8 Multiple Cuts for Two Analytes.
Figure 11.9 Deductions from the Chromatogram.
Figure 11.10 Trap‐and‐Hold Column System.
Figure 11.11 Distribution Column System.
Chapter 12
Figure 12.1 Diagnosing Process Data Trends.
Figure 12.2 Four Patterns of Baseline Disturbance.
Figure 12.3 Baseline Drift.
Figure 12.4 Baseline Wander.
Figure 12.5 Baseline Cycles.
Figure 12.6 Baseline Noise.
Figure 12.7 Chromatogram with Unstable Baseline.
Chapter 13
Figure 13.1 Overlaid Reference Chromatogram.
Figure 13.2 Typical Peaks.
Figure 13.3 Typical Spikes.
Figure 13.4 Typical Bumps.
Figure 13.5 Typical Steps.
Figure 13.6 Troubleshooting Example.
Figure 13.7 Valve Diagram.
Figure 13.8 Diagnosing Chromatogram Peaks.
Figure 13.9 Diagnosing Chromatogram Bumps.
Figure 13.10 Diagnosing Chromatogram Steps.
Guide
Cover Page
Table of Contents
Title Page
Copyright Page
Dedication Page
Contributors
Preface to the first book
Preface to the second book
Acknowledgments
Begin Reading
Answers to self‐assessment questions
Subject index of SCI‐FILEs
Glossary of terms
Index
WILEY END USER LICENSE AGREEMENT
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Process Gas Chromatography
Advanced Design and Troubleshooting
A Companion Volume of Process Gas Chromatographs (2020)
TONY WATERS
California, USA
This edition first published 2025© 2025 John Wiley & Sons Ltd
All rights reserved, including rights for text and data mining and training of artificial technologies or similar technologies. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions.
The right of Tony Waters to be identified as the author of this work has been asserted in accordance with law.
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Limit of Liability/Disclaimer of WarrantyIn view of ongoing research, equipment modifications, changes in governmental regulations, and the constant flow of information relating to the use of experimental reagents, equipment, and devices, the reader is urged to review and evaluate the information provided in the package insert or instructions for each chemical, piece of equipment, reagent, or device for, among other things, any changes in the instructions or indication of usage and for added warnings and precautions. While the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials or promotional statements for this work. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.
Library of Congress Cataloging‐in‐Publication Data applied for
Hardback ISBN: 9781119791478
Cover Design: WileyCover Image: Courtesy of ABB Inc.
For Sonia
“I pray you choose Joy.Anything else is a waste of time.”
Rev. Dr. Sonia E. Waters (1972–2023)
Process Gas Chromatographs at the INEOS Olefin Plant in Cologne, Germany.Photo © INEOS in Cologne 2019.
“We cannot teach people anything;we can only help them discover it within themselves”
Attributed to Galileo Galilei 1564‐1642
Contributors
An international team of expert chromatographers has peer reviewed the technical content of this text. This Editorial Advisory Board comprised the experienced analyzer engineers listed below. Together with the author, this team has accumulated 487 years of practical experience with process gas chromatographs. We gratefully acknowledge their contributions.
Massimo Baldizzone, PhD
Area Market ManagerABB Measurementand AnalyticsMilan, Italy.
Massimo holds both Bachelor's and Master’s degrees in Chemistry, as well as a PhD in the same field. Additionally, he has earned an Executive Master in Marketing and Sales (EMMS) from Bocconi and ESADE School of Management. Throughout his career, he served as Technical Sales Support for ABB Lewisburg Process Analytics. Currently, he holds the position of Area Market Manager for the Process Gas Chromatographs product line at ABB Measurement and Analytics.
Massimo has 15 years of experience with process gas chromatographs.
Jerry Clemons, PhD
Process GasChromatograph Consultant
Formerly, General ManagerABB Process AnalyticsRonceverte, WestVirginia USA.
Jerry has worked with gas chromatographs during his entire career starting at Virginia Polytechnic University where he earned his PhD with Dr Harold McNair.
He has held many engineering and management positions at ABB Process Analytics and its predecessors, always focused on their process gas chromatographs. Now retired from active duty, Jerry continues to provide his technical expertise as a consultant to that company.
Jerry has 50 years of experience working with process gas chromatographs.
R. Aaron Eidt, BSc
Process Analyzer ConsultantPEAK PERFORMANCEAnalytical Consulting Ltd.Delta, British Columbia, Canada.
Formerly, Analyzer and PGCManager Dow ChemicalCanada ULCFort Saskatchewan,AB, Canada.
Aaron is a chemist with 25 years of experience developing GC methods for research and industrial chromatographs at Dow Chemical Canada. Aaron specialized in process analyzer validation, troubleshooting, and performance improvement. For several years, he led the Dow Global Process Chromatography Technology Network. Since retiring from Dow, Aaron has had process analyzer consulting engagements with the Sadara Chemical Company in Jubail, Saudi Arabia, and most currently with MEGlobal.
Aaron has 35 years of experience practicing industrial gas chromatography.
Michael Hoffman
Business DevelopmentManager SiemensIndustry, Inc.Gas ChromatographySystems MAXUM LLCHouston, Texas, USA
Michael started the industry in 1979 at Phillips 66, Bartlesville, OK. The journey continued with Standard Oil Chemicals, BP, Innovene, and INEOS before Siemens, soon to be Valmet.
Michael initially worked with laboratory chromatographs but transitioned to process chromatographs in the early 1980s. Primarily focusing on online analyzer reliability, the journey expanded to advanced process control, materials handling, and analyzer data management technologies. Michael joined Siemens in 2007 and is now responsible for the marketing and technical support of analytical solutions, data communications, process GC applications, and sample system designs.
Michael has 41 years of experience working with laboratory and process gas chromatographs.
Dirk Horst
Freelance Trainer andConsultant ProcessAnalyzer and CustodyTransfer Systems
Formerly Global QMIEngineer and ConsultantShell Global SolutionsTeam The Hague,The Netherlands
Dirk has a long experience with process analyzers, including startup assignments at Shell jobsites in India, Germany, Nigeria, and Russia. He is also well known for his many classroom and practical training programs for analyzer maintenance technicians.
Dirk has 34 years of experience working with process gas chromatographs.
Junji Koyama, ME
Process GasChromatographApplication SpecialistYPHQ SystemAnalyzer CenterYokogawa ElectricCorporation Mitaka,Tokyo, Japan.
Junji‐san has been a leader of the PGC application development team at Yokogawa, holding engineering and management roles in application development and column design. Additionally, Junji‐san looks after Yokogawa's global application labs while also providing technical support to sales and service engineers.
Junji‐san has 16 years of experience working with process gas chromatographs.
Dr. Daniel Kuehne
Process GasChromatograph ConsultantHead of Global GC Proposalsand FEED SupportGas ChromatographySystems MAXUM GmbH;Part of Valmet GroupKarlsruhe, Germany.
Daniel studied Chemistry at the University of Bremen, earning his diploma and completing a doctorate thesis in Analytical Chemistry. He joined Siemens in 2005 as a method developer for process GCs. He stayed in method development for 11 years, the last 5 years as head of the PGC method developer team. In 2016, he joined the technical proposals team for PGC and worked as a technical consultant for sales and customers. Daniel has been in his current role as head of the global team for GC proposals and FEED support since 2022.
Daniel has 19 years of experience working with process gas chromatographs.
James Leonard, PhD
Senior Technical AssociateCorporate Analytical DivisionEastman ChemicalCompany Kingsport,Tennessee, USA.
James received his PhD in Analytical Chemistry from The Ohio State University. He has 24 years of experience working in the field of Process Analytics at Eastman Chemical. During this time, James has designed, installed, and commissioned analyzer systems incorporating modern on‐line techniques throughout the world. He has presented lectures on process analytics at university and other organizations to promote the use of on‐line technologies to improve process control and reduce waste.
James has 20 years of experience working with process gas chromatographs.
Harald Mahler
Business DevelopmentProfessional GasChromatographySystems MAXUM GmbHKarlsruhe, Germany.
Harald Mahler studied chemistry at Reutlingen University. Since 1989, he gained experience in process analytics from various engineering and management positions within Siemens Process Analytics; these include assignments in the applications and method development laboratory, project management, and industry marketing and product management. Currently, he is Global Sales and Business Development Manager for process analytics within Gas Chromatography Systems MAXUM GmbH. Major working areas are the (petro)chemical and oil and gas industries including decarbonization markets.
Harald has presented technical papers at several international symposia and conferences in Europe and North America. He has also authored articles in technical magazines and books and acted as session chair at several conferences.
Harald has 35 years of experience working with process gas chromatographs and other process analyzers.
Gen Matsuno, ME
Manager, AnalyzerMarketingSensing CenterYokogawa ElectricCorporation Mitaka,Tokyo, Japan.
Matsuno‐san was the leader of the Yokogawa GC8000 PGC development team. In addition to his experience of designing process gas chromatographs, he has five years of experience as a laboratory GC user.
Gen‐san has 17 years of experience working with process gas chromatographs.
Takashi Matsuura, BE
Senior Field EngineerNippon Swagelok FST, Inc.Yokohama, Japan
Formerly, Manager ofProcess GC DevelopmentYokogawa ElectricCorporation.
Taka designed the Yokogawa GC1000 PGC oven and was the leader of the engineering team that developed the Yokogawa GC1000 Mk2 PGC. He wrote the specification for the Yokogawa GC8000 PGC.
Taka has over 25 years of experience working with process gas chromatographs.
Phillip McKay
Process Gas AnalyserSpecialistAustralia and Pacific Region
Support Services Managerat Integrated AnalyticalSystems
Service Manager at TrescoInternational (Aust) Pty. Ltd.
Phil came into gas chromatography with a strong electronics background. In the early 1980s, he joined Beckman Instruments as a service engineer specializing in process gas chromatographs and a wide range of process gas analyzers. He has extensive practical experience of process analyzers including sample system design and commissioning; troubleshooting and repair; and programming and data communications interfacing. Phil also teaches introductory and advanced training courses on the operation and maintenance of process gas chromatographs.
Phil has over 40 years of experience with process gas chromatographs.
Suru Patel, PhD
Process AnalyzerConsultantPatex Controls Ltd.Calgary, Alberta, Canada.
Formerly, DistinguishedEngineering Associate forProcess AnalyzersExxon ChemicalCompany Sarnia,Canada and Singapore.
In addition to his process analyzer engineering work, Suru developed PGC training courses for process analyzer technicians and PGC data users. Previously, for several years, Suru was a PGC Applications Engineer at Servomex Company in the UK and was the Lead Analyzer Engineer in Houston for Exxon`s Singapore Chemical Complex Project. He was also the development engineer for a new flame ionization detector.
Suru has 40 years of experience working with process gas chromatographs.
Eric Schmidt, PhD
R&D FellowThe Dow Chemical CompanyAnalytical SciencesFreeport, Texas, USA.
Eric Schmidt received his PhD in Analytical Chemistry from The University of Texas at Austin. He has worked at the Dow Chemical Company in Freeport, TX, for over 25 years as a Research Scientist where he spends his time developing new on‐line process measurements for R&D and manufacturing. He is currently leading the On‐line Chromatography Strategic Capability Team at Dow.
Eric has 20 years of experience working with process gas chromatographs.
Ivan Rybár, PhD
Head of the Electrical andAutomation MaintenanceSlovnaft Refinery MaO, a.s.Bratislava, Slovakia.
Formerly, Research andTeaching Assistant,Department of AnalyticalChemistry Comenius UniversityBratislava, Slovakia.
For 15 years, Ivan has been responsible for the reliability of process analyzers at the Slovnaft refinery, including managing the maintenance of existing systems and designing new analytical equipment. During his career, he worked on more than 120 projects. As a supervisor for process analyzers, he creates work procedures and provides consultation and support to his team.
He was awarded the accolade “Slovnaft Star” twice, in 2013 and 2015.
Previously, he worked as an analyzer engineer for several companies providing engineering services to industrial plants, including the selection of analyzers and the design of entire sampling systems.
During his time at the university, Ivan developed new methods in liquid chromatography, taught several postgraduate courses, and published four scientific papers in this field.
Ivan has 20 years of experience working with process gas chromatographs.
Preface to the first book
Welcome to the world of Process Gas Chromatography!
This book (Waters 2020) focuses on the Process Gas Chromatograph (PGC). There are dozens of fine books on the science of gas chromatography but few on the technology of the process instrument. I found only two previous books dedicated to online gas chromatographs (Huskings 1977; Annino and Villalobos 1992).
Process gas chromatographs are complex instruments and the people that design and operate them need special knowledge and unique skills. With that in mind, I designed the book to serve the needs of the journeyman analyzer technician, the process instrument engineer, and the process analyzer specialist.
PGC is a practical technology and this is a practical book. It’s an effective classroom training manual for those currently learning the art and a handy reference manual for those already practicing it.
Chapters are deliberately compact, suitable for a weekly reading program or as focused lessons in an educational course. Each chapter ends with a summary of knowledge gained and a self‐assessment quiz with answers provided. In addition, there are nine optional test questions for students; three easy, three moderate, and three challenging.
Why is such a book necessary?
Anyone working in the fluid processing industries knows that their knowledge base is in full flight. Due to staffing reductions and mass retirements, our industry is losing decades of hard‐won experience.
Walter Jennings and Colin Poole recently expressed this situation rather well (Jennings and Poole 2012, 16):
This [automation of gas chromatographs] has led to a continuing decline in the expertise of the average practicing chromatographer from the mid‐1980s to the present time. This can be perilous, because everything from column selection to trouble‐shooting skills is based on a fundamental knowledge of chromatographic principles, the absence of which degrades the quality and usefulness of the information acquired by these instruments. To address these problems requires a massive educational effort before the knowledge is lost and the usefulness of gas chromatography to decision makers is called into question.
There can be no clearer call to justify this book. While the authors were writing to laboratory chemists, those working on process gas chromatographs also need a fundamental knowledge of chromatographic principles presented in a way that facilitates a massive educational effort. This book sets out to satisfy those needs. It’s primarily written for process analyzer engineers and technicians but should be helpful to anyone using or maintaining a process gas chromatograph.
To succeed in its mission, a book needs to so excite the reader that they want to read more. It should be so useful that they immediately return to it when they need information. Yet the average book on gas chromatography is abysmally boring and poses an intellectual challenge even to post‐doctoral scientists, let alone the lonely guy faced with fixing a broken process chromatograph at midnight.
This text teaches the fundamental knowledge of process gas chromatography by encouraging the reader to think critically about what is happening in the instrument, mostly without recourse to analogy or math. It also describes some practical procedures for design or troubleshooting.
So, here you have it. A clear yet detailed book that is ideal for classroom instruction, private study, or distance learning. Focused chapters unfold the technology of a process gas chromatograph to an engineer or technician who may have no previous experience of the technique. The content is basic, yet thorough, so it should meet the needs of many readers.
I’m glad that you’re here. I hope you enjoy the book!
Tony Waters
Atascadero, California
January 2020
Preface to the second book
Welcome back to the world of Process Gas Chromatography!
This second book about process gas chromatographs picks up from its predecessor, going deeper into PGC application and care. As such, companion volume to the first book takes off where the first one landed. The focus here is on the columns and the chromatograms they generate. We take a detailed look at how to design chromatographic columns, how to make them work together to speed analysis, and how to diagnose symptoms that presage trouble.
There’s more than enough theory here, but it’s mostly set out in optional SCI‐FILES for those who need to know the mathematical foundation for the practical procedures given. This compilation of theoretical and practical knowledge is a highly focused resource for applications engineers who design column systems for industrial applications, for service engineers who maintain them, and for anyone else working with gas chromatographic columns. Analytical chemists in industrial laboratories, pilot plants, and academia will appreciate the detailed information on column design and the automation of routine chromatographic analyses.
Unless you’re very familiar with process gas chromatographs, you’ll want to own both books. They work together to provide a complete knowledge of the technology without reference to the subtleties of the brand. This second book is designed not only to support an advanced‐level course in Process Gas Chromatography but also to serve as a handy reference to anyone needing a quick answer to an immediate problem. It is a great reference source to have by your side when you need it.
Enjoy your work with process gas chromatographs!
Tony Waters
Atascadero, California
August 2024
References Cited
Annino, R., and Villalobos, R. (1992).
Process Gas Chromatography
. Research Triangle Park, NC: Instrument Society of America. ISBN: 1‐55617‐272‐9.
Huskings, D.J. (1977).
Gas Chromatographs as Industrial Process Analyzers
. New York, NY: Pergamon Press, Inc.
Jennings, W.G. and Poole, C.F. (2012). Milestones in the development of gas chromatography. In:
Gas Chromatography
(ed. C.F. Poole), 1–17. Oxford, UK: Elsevier. ISBN: 978‐0‐12‐385540‐4.
Waters, T. (2020)
Process Gas Chromatographs: Fundamentals, Design and Implementation
. Chichester, UK: John Wiley & Sons Ltd.
Waters, S.E. (2023).
Letter to the President, Princeton Theological Seminary
. Princeton, NJ.
Acknowledgments
Hearty thanks to friends and associates who contributed material to this text. Their valuable contributions of time and knowledge are much appreciated.
Andy EvansAnalyzer EngineerDow CorningSwansea, Wales, UK.
Jay BrownGeneral ManagerOhio Valley SpecialtyCompany Marietta,Ohio USA.
Daren BrumleySenior TechnicalInstructorABB Process AnalyticsSkiatook, OklahomaUSA.
Damian HuffSenior PGCApplications EngineerABB Process AnalyticsBartlesville,Oklahoma USA.
Andrzej JopekDirectorProcess AnalyticalMiddle East WLLBahrain.
Fusan KaraburunTechnical ProductOwnerQmicron B.V.Enschede,Netherlands.
Dorothy KwidamaTechnical ProductSpecialistQmicron B.V.Enschede,Netherlands.
Bert LaanProcess AnalyserConsultantOlpass LtdHereford,England UK.
Ryan McSherryAnalyticalSolutionsYokogawaCorporation ofAmericaNewnan,Georgia USA.
Nicholas MeyerManager—Industryand Product MarketingYokogawaCorporation ofAmericaNewnan,Georgia USA.
Martin PijlProduct Manager GasAnalyzersYokogawa Europe B.V.Amersfoort, Netherlands.
Wouter PronkBusinessDevelopment & TrainerB.E.S.T. FluidsystemeGmbH Neuss,Germany.
Asad TahirDirector of Product ManagementEmerson Process ManagementHouston, TexasUSA.
John WassonPresidentWasson‐ECEInstrumentationFort Collins,Colorado USA.
Henk van WellManager AnalytischTechnischerServiceINEOS ManufacturingDeutschlandGmbH Köln,Deutschland.
Dr. Martin WieserProcess AnalyzerEngineerBASF SELudwigshafen,Germany.
A Modern Process Gas Chromatograph.
Source: Reproduced with permission from Yokogawa Electric Corporation.
1Fundamentals
“This is our second book on the process gas chromatograph. Written as a companion volume, this book doesn’t supersede its predecessor; it builds on that firm foundation to examine the special nature of process gas chromatography rather than the process instrument itself.”
Introduction
Academic theories of gas chromatography have been hugely successful in explaining the chromatographic process and predicting ways to improve its performance. Many books and scientific papers are available to those looking for a rigorous dissertation on the subject, but they are often inscrutable. This book takes a pragmatic approach without disregarding well‐established theory. As optional reading, separate SCI‐FILEs located at key moments throughout the book capture a simplified and accessible explanation of the relevant science. There’s a list of these technical asides in Appendix B.
We assume the reader has a good understanding of PGC hardware gained from practical experience or from studying our previous book. That said, this chapter has the simple goal of introducing some of the concepts and terminology used herein.
Gas chromatography
A unique analytical technique
Gas chromatography1 is a powerful method of chemical analysis that has been adapted for use in industrial processes to measure the concentration of selected chemical substances in a small sample of the process fluid.
The chemicals present in the sample are known as components. Of these, the ones actually measured are the analytes. An analyte is usually a single chemical substance but sometimes can be several components measured together as a group.
Unlike other process stream analyzers, a PGC doesn’t try to measure a desired analyte in the presence of the other substances in the sample. It’s always difficult to do that. Instead, it separates each target analyte from everything else and then measures it independently. The two‐stage procedure of separation‐before‐measurement is why the PGC is so versatile. It allows a PGC to measure almost anything in any process gas or volatile liquid.
A basic gas chromatograph
Figure 1.1 shows the main parts of a basic gas chromatograph. To start an analysis, the sample valve injects a discrete sample of the process fluid into a stream of inert carrier gas, typically hydrogen, helium, or nitrogen. The injected sample can be a gas or a volatile liquid that immediately vaporizes. The flowing carrier gas immediately carries the vapor sample into the column, a narrow tube containing an active solid or an immobilized liquid. As they pass through the column, the analytes separate from the other components and from each other, arriving at the end of the column at different times. In practice, most PGCs need two or more columns to fully separate the analytes. Then, each analyte passes in turn through a detector, which senses its presence and outputs an electronic signal proportional to its concentration in the original sample.
When expressed in more formal terminology:
The carrier gas is the
mobile phase
.
It’s the driving force that powers the chromatography.
The active solid or immobilized liquid is the
stationary phase
.
It’s the agent that creates the separation.
Figure 1.1 A Basic Gas Chromatograph.
A mobile phase moving in contact with a stationary phase is the essence of chromatography. In gas chromatography, the mobile phase and the sample (after injection) are both gases. In another kind of chromatography, the mobile phase and the sample are both liquids. That’s liquid chromatography, a technique rarely used in process analyzers and not further discussed herein.
The columns
As the carrier gas carries the analytes through the column, they experience an affinity for the stationary phase which delays their progress more or less than the other components. A careful choice of stationary phases can combine these delays to accomplish a complete time‐separation of the desired analytes.
PGC column systems are custom designed to isolate the desired analytes from all the other components in the sample. An applications engineer chooses the stationary phases and an arrangement of columns to accomplish that. The special techniques of column design, optimization, and troubleshooting are the core subjects of this book.
Gas chromatographs employ two types of column:
A
packed column
is typically a ⅛″ or ″ o.d. tube closely packed with small particles. In a solid‐phase column the particles themselves are the adsorbent solid that performs the separation. In a liquid‐phase column the particles are inert but they have a thin coating of the selected liquid phase.
A
capillary column
is typically a long 0.53 mm (or smaller) i.d. tube that has an internal wall coating. Most capillary columns have the selected liquid phase coated or chemically bonded to their inner walls. A few have a finely powdered solid adsorbent on their walls.
The detector
After a predictable delay, each analyte emerges from the column system as pure vapor diluted with carrier gas, an easy mixture to measure. The carrier gas carries it into a detector which responds with an electronic signal to the data processor.
As each component emerges from the column system the detector signal gradually increases from its quiescent baseline level, transits through a maximum, and then decays back to the baseline forming a nearly symmetrical peak shape over time. Analyte peaks are typically between 1 and 10 seconds wide and separated in time from all other peaks.
It’s normal to refer to the bands of solute molecules migrating along the column as “peaks” even before they reach a detector.
A PGC uses the elapsed time between sample injection and peak apex to identify each analyte peak. It also measures the area of each analyte peak to determine its concentration in the original sample. The concentration is usually a linear function of the peak area, a relationship established by calibration.
The chromatogram
The detector signal viewed as a function of time is a chromatogram. The chromatogram contains all the analytic information generated by a PGC and a display or printout is indispensable for design, maintenance, or troubleshooting work. In normal operation, though, the PGC processes the detector signal automatically and displays a visible chromatogram only on demand.
Figure 1.2 shows a chromatogram as displayed on a typical PGC. This one shows the separation of small amounts of aromatics2 and higher paraffins in natural gas. The C11 and higher components are backflushed3 and elute first as a partly regrouped composite peak.
Figure 1.2 A Typical PGC Chromatogram.
Source: Reproduced with permission from ABB, Inc.
The science of GC
The theory of gas chromatography is complex and its technology intricate, but once you get past all the equations, the simplicity of the core science may come as a shock. We introduce it here and define some of the terms we use.
The basic science
The two forms of gas chromatography use different stationary phases, solid or liquid. Their mechanisms of separation are different. Solid phases delay components by adsorbing their molecules onto an active surface, whereas liquid phases delay molecules by dissolving them. Yet the result is much the same: the molecules can’t move while dissolved or adsorbed by the stationary phase. Solid phases have a strong affinity for gas molecules, which makes them suitable for separating low‐density gases such as hydrogen, oxygen, nitrogen, carbon oxides, and lighter hydrocarbons. Liquid‐phase columns separate most other components, so the majority of PGC columns have liquid stationary phases. Let’s see how those work.
When in the vapor phase most substances will dissolve in a liquid, but to different degrees. Two technical terms apply to the resulting solution:
The substance dissolving in the liquid is the
solute
.
It’s a general term for any component of the analyzed sample retained by the stationary phase.
The liquid dissolving the solute is the
solvent
.
We usually just call it the liquid phase.
We rarely use the word solvent in process gas chromatography because it can be confusing. The confusion arises from the common laboratory practice of dissolving samples in a solvent before injecting them into a gas chromatograph. This creates a huge solvent peak on the chromatogram. PGCs don’t dilute their samples, so solvent peaks don’t occur.
Let’s examine what happens when a solute contacts a stationary phase. When a small amount of sample gas enters an enclosed space containing a gas and a liquid, solute molecules distribute themselves between the gas phase and the liquid phase. This happens because molecules possess kinetic energy and move rapidly and randomly in every direction. Their motion brings them into contact with the liquid surface where some of them dissolve. Then, as their number in the liquid phase increases, they start to reenter the gas phase. This rapid exchange inexorably leads to a situation where their rates of arrival and departure at the liquid surface become equal, forming a dynamic equilibrium. It then seems like nothing is happening because the number of solute molecules in each phase remains constant. Yet solute molecules continue to move rapidly between the phases.
At equilibrium, the solute concentration in the gas phase and the solute concentration in the liquid phase are both constant, but not identical. Their values depend only on the temperature and the inherent solubility of the solute in the selected liquid.
Then:
The ratio of solute concentration in the liquid phase to solute concentration in the gas phase is the
distribution constant
.
Increasing the temperature reduces the distribution constant, and vice versa.
The distribution constant4 is the fundamental science of chromatography. In a column, it determines the number of dissolved solute molecules left behind when the gas phase moves, carrying with it the undissolved solute molecules. We shall see that the position of each peak on the chromatogram is a simple function of its distribution constant.
The science of chromatography comes down to this simple concept: gases dissolve in liquids to different extents.
That’s it. Chromatographic separation occurs because different sample components each have their own unique solubility in the liquid phase. As the carrier gas moves, the more soluble solute molecules tend to stay in the liquid phase, delaying them longer than those having lower solubility. When their solubility difference is sufficient the solutes separate from each other.
No chemistry is involved. Interaction with the stationary phase is a simple physical process of dissolving in a liquid or adsorbing onto a solid surface.
If that was all, this book would be very short and gas chromatography would be simple, as indeed it was in the early days. Back then, two incompatible needs pulled process and laboratory chromatography apart, dragging them both into realms of increased complexity:
In the laboratory, sample composition is often unknown, so there’s a need to separate
and identify
many components – sometimes hundreds of them. The eventual solution was to use a capillary column and continually raise its temperature during analysis to separate dozens of components, a procedure known as
temperature programming
. Then, a mass spectrometric detector can identify and measure the plethora of peaks.
In the process plant, the stream compositions are known and the PGC measures only a few designated analytes. Barring simple mistakes, there’s rarely an issue with peak identity but the process control systems need fast results – sometimes in less than one minute. The eventual solution for the fastest separation was to use multiple columns and special valves to direct each component peak into the desired column.
The employment of multiple columns is a distinctive hallmark of process gas chromatographs. Although a few multiple‐column arrangements have migrated into the laboratory, it’s still uncommon to find more than one column in a laboratory gas chromatograph. In contrast, virtually all PGCs use multiple columns to separate and measure a few known analytes in the shortest time with the highest reliability and lowest cost.
Temperature programming is a distinctive hallmark of laboratory gas chromatographs as most use it to separate and identify large numbers of analytes. The technique is available in modern PGCs but when designed for autonomous operation in hazardous environments it tends to be costly and demand more maintenance than an isothermal analyzer. Therefore, PGCs employ temperature programming only when it confers a significant advantage.
The gas chromatograph
The basic instrument
A gas chromatograph is an analytical instrument that uses the techniques of gas chromatography to measure the concentration of selected chemical compounds in a small sample containing a mixture of compounds.
The essential hardware devices found in any gas chromatograph include:
One or more temperature‐controlled zones.
A carrier gas supply and pressure control system.
A sample injector that injects a repeatable volume of sample into the flowing carrier gas.
One or more separating columns.
One or more detectors.
A processor to control operations and calculate results.
While all gas chromatographs have these basic functions, there are large variations in their design and fabrication.
The process instrument
A gas chromatograph working at an industrial processing plant is strikingly different from a gas chromatograph sitting on a laboratory bench. The main reasons for these differences are:
The PGC operates in a potentially hot, cold, dusty, wet, windy, corrosive, or hazardous environment.
The PGC operates continuously 24 hours per day, 7 days per week.
The PGC must operate reliably with almost no human intervention – perhaps only one calibration check each month.
The PGC applications engineer knows in advance the components and concentrations expected in the sample.
The PGC can focus on measuring just a few of the components in a sample – the ones needed for process control.
The PGC suffers a fanatical quest to minimize the analysis time, to ensure that its measurements are valid for process control.
For all the above reasons, a process gas chromatograph may include some devices and properties not shown in Figure 1.2, such as:
External devices to condition the incoming process sample to make it compatible with the PGC; that is, a
sample conditioning
system.
Multiple columns with special devices to switch analyte molecules from one column to another, thus maximizing the rate that separated components arrive at the detector. Laboratory instruments rarely need this additional complexity.
Housekeeping columns
that allow strongly retained components to quickly exit the column system. These are also becoming popular in laboratory chromatographs used frequently for routine analyses. Those used only a few times each day have plenty of time to recover between sample injections.
Robust column systems and stable devices, all designed to operate for a long time without adjustment.
Hardened microprocessor systems to capture and process the detector signal and to schedule timed events.
Self‐diagnostics and alarm generation and optional software for centralized maintenance.
Optional applications software for autonomous validation and statistical quality control.
Protected and suitable for continuous operation in a dirty, corrosive, and potentially hazardous environment.
Housed in an analyzer shelter or building to protect the analyzers and the workers from the plant environment.
For further information, refer to our companion book on the hardware of process gas chromatographs (Waters 2020). The present volume focuses on the design, optimization, and troubleshooting of PGC column systems.
The contents
Here’s a brief review of the information this book contains.
Chapter 2 illustrates a few simple chromatogram measurements we can make to evaluate and optimize column performance.
When looking at a chromatogram an inexperienced observer sees a range of mountain peaks on a flat plain. There’s so much more to see. From a few simple measurements we learn what’s going on in the columns and find ways to optimize their performance. The chapter also introduces the use of plate theory to explain and then quantify peak shape, separation, and resolution.
Chapter 3 is a detailed review of PGC column technology, comparing and contrasting the structure and properties of the different kinds of columns.
This practical chapter describes how packed and capillary columns are made and how they work. It examines in fine detail the molecular forces involved in various mechanisms of separation and defines what we mean by the affinity between a solute and a stationary phase.
Chapter 4 examines the choice of PGC stationary phases and tabulates the properties of many solid and liquid phases.
This is a detailed review of the liquid and solid stationary phases typically used in process gas chromatography. It provides practical guidance on the use of Kovâts indexes and McReynolds constants for selecting a suitable liquid phase and gives the polarity factors for many liquids.
Chapter 5 recognizes the need to tune the stationary phase to deliver the best resolution between analyte peaks in the shortest time.
It expounds the theories of distribution and resolution and examines the practical consequences, deducing the optimum conditions for maximum resolution of peaks. This leads into a practical example that shows how to obtain improved resolution in less analysis time.
Chapter 6 introduces the rate theory of gas chromatography and explains its use for optimizing the operating conditions of a single column.
You’ll learn how to determine the optimum carrier gas flow rate and why it’s not used in process chromatographs. A practical example illustrates the optimization of flow and column length, achieving the same or better resolution in less time by using a longer column!
Chapter 7 discusses the causes and remedies for asymmetric peaks.
Real peaks are slightly skewed, they rise to their apex a little faster than they decline to their baseline. This minor asymmetry isn’t a problem. But some peaks are grossly misshapen and we need to know why. Here, we discover the reasons for tailing and fronting (or “leading”) peaks and what we can do to minimize the problem: the handy troubleshooting table given here might be helpful.
Chapter 8 identifies causes for peak broadening in the analyte flow paths external to the column.
Peaks become wider as they travel through devices such as the sample injector, column valve, detector, or even connecting tubing. If significant, this broadening can spoil a perfect resolution. The text gives quantitative methods for evaluating these effects and suggests some ways to minimize their influence on column performance.
Chapter 9 examines the effect of the pressure gradient in series columns.
Most process gas chromatographs employ multiple column arrangements to achieve the necessary separation in the shortest possible time and this results in columns working at different pressures. While the mass flow rate is constant within columns in series, the volumetric flow varies with the pressure. The chapter develops quantitative methods for determining the retention times of peaks in each column and gives some examples for the calculation of column lengths.
Chapter 10 examines the backflush column system in detail, giving both theoretical and practical outcomes.
Neary all PGC column systems include a backflush function, so it’s essential to understand its function and its quirks. The text describes backflush column systems using valve and valveless arrangements, then looks at why practical outcomes differ from the theoretical ideal. The discussion includes the optimization of column lengths.
Chapter 11 examines the heartcut column system in detail, giving both theoretical and practical outcomes.
PGCs always use the heartcut function to measure low concentrations of impurities in otherwise pure samples. The chapter explains why heartcut is necessary and then describes heartcut column systems that use both valve and valveless column switching. The discussion includes the column design features necessary for successful operation of single and multiple heartcuts.
Chapter 12 describes useful troubleshooting techniques for diagnosing baseline problems.
When only carrier gas is emerging from the column, the chromatogram should display a flat baseline with no change over time. If not, any visible disturbance is a potential symptom of trouble. The discussion includes diagnostic techniques for finding the root cause of drifting, wandering, cycling, or noisy baselines. The extensive troubleshooting tables may be helpful.
Chapter 13 describes useful troubleshooting techniques for diagnosing chromatographic problems.
After obtaining a flat and smooth baseline any symptoms that remain must be due to the cyclic operation of the PGC analysis. The often subtle symptoms of incipient failure may escape the notice of a casual observer but are bright red flags to an experienced troubleshooter. They include unexpected peaks, spikes, bumps, or steps in the baseline. The extensive troubleshooting tables may be helpful.
The Glossary of terms is an extensive dictionary of the technical terms and expressions used in gas chromatography and a useful resource. It also includes the name, formula, and molar mass of many chemicals found on chromatograms. If you’re uncertain about the meaning of an English word or phrase, look it up in the Glossary!
Becoming a PGC expert
In contrast to holistic methods of analysis, measuring an isolated analyte is simple and rarely troublesome. But the chromatographic process used to secure that isolation is not so easy to understand. It’s often arcane and hard to grasp. We intend to demystify that process by describing many practical ways to evaluate and optimize column performance or diagnose column malfunction.
It turns out that most of the evidence you need is plainly visible on the chromatogram and the secret skill of the expert is simply knowing how to decipher the information it contains.
The secret skill of the PGC expert is their ability to read a chromatogram and understand what it’s telling them.
The chromatogram readout is a vital design and troubleshooting tool; so much so that it’s difficult to overstate its usefulness. Discounting calibration errors and electrical failures that are easy to fix, all faults are visible on a chromatogram, either directly or by comparing the current chromatogram with a previous one.
If you aspire to be an expert PGC applications engineer or troubleshooter, learn to read the chromatogram. You’ll find the knowledge you need on the following pages.
Knowledge Gained
Chromatography uses a fluid mobile phase passing over a liquid or solid stationary phase
.
In gas chromatography, the mobile phase is gas; in liquid chromatography, the mobile phase is liquid
.
Chromatographic analyzers separate the desired analytes and then measure them one by one
.
Other analyzers attempt to measure the analyte molecules in the presence of other molecules
.
Gas chromatographs inject a tiny volume of sample into the flowing carrier gas
.
The sample must be a gas or a volatile liquid that quickly vaporizes and enters the column as a vapor
.
Process gas chromatographs (PGC) use an automatic injection valve to inject the sample
.
The carrier gas carries the sample into the column where it contacts the stationary phase
.
The stationary phase may be a solid adsorbent or an immobilized nonvolatile liquid
.
Contact with the stationary phase delays some peaks more than others, so separation occurs
.
Special routing devices may direct the peaks into different columns to finish the desired separation
.
PGCs can use either packed columns or capillary (open tubular) columns
.
The separation process takes time; typically 1 to 10 min, sometimes longer
.
The carrier gas elutes peaks from the column into a chosen detector for measurement
.
The detector responds to a property of analyte molecules that differs from carrier gas molecules
.
The detector output signal forms a chromatogram display when plotted against elapsed time
.
Analyte molecules cluster together at different times to form separate chromatogram peaks
.
The PGC typically measures peak area to compute the concentration of an analyte
.
The chromatogram is a most valuable source of information, but one must learn to read it
.
To the expert troubleshooter, all chromatographic faults are visible on the chromatograms
.
Did You Get It?
Self‐assessment quiz: SAQ 01
Q1. In gas–liquid chromatography, what are the gas and liquid doing?
Select the one correct answer:
They are both moving.
The gas is moving and the liquid is stationary.
The gas is stationary and the liquid is moving.
They are both stationary.
Q2.
In gas chromatograph, which of the gases listed below would be suitable as the carrier gas?
Select all the correct answers:
Oxygen
Nitrogen
Hydrogen
Helium
Q3.
In gas–liquid chromatograph, which one of the materials listed below might be the stationary phase?
Select the one correct answer:
An inert gas
A granular adsorbent solid
A volatile liquid
A nonvolatile liquid
Q4.
In gas–liquid chromatograph, what really causes the separation?
Select the one best answer:
The carrier gas causes the separation.
The mobile phase causes the separation.
The stationary phase causes the separation.
The chromatogram causes the separation.
Q5.
In gas chromatograph, what do the columns do?
Select the one best answer:
They convert all the components into peaks.
They separate the analytes from all other components and from each other.
They separate all the components of the sample.
They allow only measured components to enter each detector.
Q6.
In gas chromatograph, what does a detector do?
Select the one best answer:
It provides a continuous flat baseline as a reference for measuring the peaks.
It generates a signal proportional to the instantaneous number of component molecules leaving the column.
It measures the area of each peak.
It converts each component of the sample to a concentration.
Q7.
Why is the chromatogram so important?
Select the one best answer:
It shows the baseline used for measuring the peaks.
It shows the shape of each peak.
It shows the separation between peaks.
All of the above.
Check your SAQ answers with those given at the end of the book.
References
Further reading
The companion book (Waters 2020) establishes the basic functions and hardware of the PGC and is essential reading to those who desire a full understanding of the equipment.
The 26‐page encyclopedia article by Clemons (2011) is an excellent review of process gas chromatographs and their applications in industry. It’s highly recommended for those seeking a wide overview of the techniques and applications of the PGC.
The delightful book by Ettre (2008) is an interesting historical account of the development of chromatographic science by one who was there.
