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Chapter 24: Q20p (page 663)

Retention time depends on temperature, T, according to the equation log t’r =(a/T) + b, where a and b are constants for a specific compound on a specific column. A compound is eluted from a gas chromatography column at an adjusted retention time t’r =15.0 min when the column temperature is 373K. At 363 K, t9r 5 20.0 min. Find the parameters a and b and predict t’r at 353K

Short Answer

Expert verified

The relationship between temperature T and retention time(t'r)is shown below:

logtr'=aT+b

where: a and b are constants for a specific compound and specific column

List the given:

-tr'=15.0minatT=373Kt'r=20.0minatT=363K

Step by step solution

01

constant a and b

Find:

- a and b

- t'rat353K

First, to find the parameters a and b, we can set-up two equations from the given t'rand T.

Setting up Equation 1

log(15)=a373+bmultiplyingbothsidesby373:438.6820=a+373b(Equation1)SettingupEquation2:log(20)=a363+bMultiplyingbothsidesby363:472.2739=a+363b(Equation2)

Solve for parameters a and b using Equations 1 and 2:

a=1691.658b=-3.3592

02

Step 2:b) t'r at 353 K 

log(tr')=aT+blog(t'r)=1691.658353+(-3.3592)log(tr')=1.4330t'r=27.10min

03

final answer

t'r=27.10min

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Most popular questions from this chapter

Oxalate is a naturally occurring substance found in plant foods such as fruits and vegetables. Within the body it can combine with calcium to form kidney or urinary stones. Determination of oxalate in food is important because of the potential for harmful effects on health. Search the literature for a headspace gas chromatography method for the determination of oxalate in food and answer the following questions.

(a) Give the citation (authors, title, journal name, year, volume, pages) for a research paper describing this analysis.

(b) What type of gas chromatography detector is used? Why is this detector appropriate?

(c) What are the precision, limit of quantification, and linear range of the method?

(d) How was the gas chromatographic determination validated?

(e) What alternative methods could be used for determining oxalate in food?

(f) Challenge question: What type of column was used?

(a) What are the advantages and disadvantages of temperature programming in gas chromatography?

(b) What is the advantage of pressure programming?

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The graph shows van Deemter curves for n-nonane at . in the 3.0-m-long microfabricated column in Box 24-2 with a -thick stationary phase.

van Deemter curves. [Data from G. Lambertus, A. Elstro, K. Sensenig, J. Potkay, M. Agah, S. Scheuening, K. Wise, F. Dorman, and R. Sacks, "Design, Fabrication, and Evaluation of Microfabricated Columns for Gas Chromatography," Anal. Chem. 2004, 76, 2629.]

(a) Why would air be chosen as the carrier gas? What is the danger of using

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(b) Measure the optimum velocity and plate height for air and for carrier

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