Tony Waters - Process Gas Chromatographs

2 Q2. In a gas chromatograph, which one of the gases listed below would not suitable as the carrier gas?Select the one correct answer:OxygenNitrogenHydrogenHelium

3 Q3. In a gas‐liquid chromatograph, which one of the materials listed below might be the stationary phase?Select the one correct answer:An inert gasA granular adsorbent solidA volatile liquidA non‐volatile liquid

4 Q4. In a 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.

5 Q5. In a 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.

6 Q6. In a 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 either the area or the height of each peak.It converts each component of the sample to a concentration.

7 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.

Your instructor will provide the answers to these test questions.

1 S1. In gas‐liquid chromatography, what is the physical state of the mobile phase?Select the one best answer:GasGas or liquidLiquidSolid

2 S2. In gas‐liquid chromatography, what is the physical state of the stationary phase?Select the one best answer:GasGas or liquidLiquidSolid

3 S3. In gas‐liquid chromatography, what is the physical state of the injected sample?Select the one best answer:GasGas or liquidLiquidSolid

4 S4. According to the chapter text, what is a typical number of analyses done per day by a process gas chromatograph, relative to the number done by a laboratory gas chromatograph?Select the one best answer:About 80 times as manyAbout 120 times as manyAbout 240 times as manyAbout 720 times as many

5 S5. According to the chapter text, what is the main function of a housekeeping column?Select the one best answer:To separate all the measured components.To separate only the unmeasured components.To allow strongly‐retained components to quickly exit the column system.To permanently absorb one or more unmeasured components.

6 S6. Imagine you are changing a PGC from liquid sample injection to gas sample injection and the gas sample will be at atmospheric pressure. If the previous liquid sample volume was 1 μL, what new gas sample volume would you install to get about the same peak heights?Select the one best answer:0.001 mL0.3 mL0.9 mL3.0 mL

7 S7. PGC detectors may not respond to every analyte. Consider the statements below; which statements are correct?Select all of the correct statements and none of the incorrect statements:No detector can respond to hydrogen sulfide, H2S.The thermal conductivity detector does not respond to hydrocarbons.The flame ionization detector is very sensitive and can measure low concentrations of carbon dioxide, CO2.The flame photometric detector does not respond to carbon monoxide, CO.

8 S8. What is a chromatogram, and why is it important?From the list below, select all the correct statements and none of the incorrect statements:The chromatogram is a graphical plot of the detector signal against elapsed time.On a chromatogram, the horizontal axis represents elapsed time, which always increases from left to right, with the zero‐time marker on the far left.On the chromatogram from a modern process gas chromatograph, the vertical axis represents the concentration of the analytes and is scaled from zero to 100 %.Chromatographic faults produce symptoms visible on the chromatogram that an expert user can diagnose.

9 S9. How is each analyte peak on the chromatogram measured?From the list below, select all the correct statements and none of the incorrect statements:Most modern PGCs measure the peak height, but a few measure the peak area.To calculate the concentration of an analyte, the PGC multiplies the analyte peak height or peak area by a stored calibration factor.The calibration factor depends on the detector in use but is the same for each analyte in the sample.The calibration factors come from the analysis of a calibration sample containing known concentrations of the analytes.

1 Ettre, L.S. (2008). Chapters in the Evolution of Chromatography (ed. J.V. Hinshaw). London, UK: Imperial College Press.

2 Harvey, D. (2017). Gas chromatography. In: LibreTexts, Section 2.4 (updated July 28, 2017), accessed October 23, 2018 at https://chem.libretexts.org

3 Rahman, M.M., El‐Aty, A.A., Choi, J., Shin, H., Shin, S.C., and Shim, J. (2015). Basic overview on gas chromatography columns. In: Analytical Separation Science (eds. J.L. Anderson, A. Berthod, V. Pino, and A.M. Stalcup), 823–834. Verlag, Germany: Wiley‐VCH. doi:10.1002/9783527678129.assep024

4 Waters, T. (2017). The fine art of chromatogram reading. Proceedings of the 2017 Analysis Division Symposium, Pasadena, California (April 24–26, 2017). Research Triangle Park, NC, USA: International Society of Automation.

1 1.1 A Classic PGC

2 1.2 A Basic Gas Chromatograph

3 1.3 Typical Gas Sample Injector Valve

4 1.4 Typical Chromatographic Columns

5 1.5 A Simple Column Switching System

6 1.6 Three Kinds of Capillary Column

7 1.7Typical Strip‐Chart ChromatogramTypical On‐Screen Chromatogram

8 1.8 A Real Chromatogram

When first introduced, these words and phrases were in bold type. You should now know the meaning of these technical terms. If still in doubt, consult the Glossary at the end of the book:

1 active‐solid column

2 analysis time

3 analyte

4 application engineering

5 atmospheric referencing

6 autosampler

7 baseline

8 calibration factor

9 capillary column

10 carrier gas

11 chromatogram

12 chromatogram signal

13 chromatograph

14 chromatography

15 column

16 column oven

17 column valve

18 component

19 detector

20 elute

21 flame ionization detector

22 flame photometric detector

23 gas chromatograph

24 gas chromatography

25 gas‐liquid chromatography

26 gas‐solid chromatography

27 housekeeping column

28 inert support

29 liquid chromatography

30 liquid loading

31 liquid‐phase column

32 mobile phase

33 molecule

34 open‐tubular column

35 packed column

36 peak

37 peak area

38 peak height

39 PLOT column

40 retention time

41 sample

42 sample conditioning

43 sample injector valve

44 SCOT column

45 separation

46 stationary phase

47 supercritical fluid

48 temperature programming

49 thermal conductivity detector

50 volatile liquid

51 WCOT column

In addition, we introduced several chemical names and you need to know what they are. If you are not familiar with chemical names, refer to the SCI‐FILE: On Chemical Names in Chapter 4. You can also look up individual chemical names in the Glossary.

1 1There are some exceptions to the principle of instant vaporization that are beyond the scope of this introductory text.