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Chapter 24: Q19P (page 663)

(a) Write the meaning of the retention factor, , in terms of time spent by solute in each phase. (b) Write an expression in terms of for the fraction of time spent by a solute molecule in the mobile phase. (c) The retention ratio in chromatography is defined as
$R = \frac{time for solvent}{time for solute to pass through column} = \frac{t_{m}}{t_{r}}$ Show that is related to the retention factor by the equation $R = 1 / k + 1$

Short Answer

Expert verified

$a) k = \frac{t_{s}}{t_{m}} b) 鈬� \frac{1}{1 + k} c) R = \frac{1}{1 + k}$

Step by step solution

01

Define Retention Factor:

The retention factor, also known as the capacity factor (k), in column

chromatography is defined as the ratio of time an analyte is retained in the

stationary phase to time

02

To find the retention Factor :

a) To calculate the retention factor as

$k = \frac{t (solute in the stationary phase)}{t (solute in the mobile phase)} k = \frac{t_{r} - t_{m}}{t_{m}} k = \frac{t_{s}}{t_{m}}$

$t_{r}$ is actually the retention time of solute of interest

03

To find the fraction of time spent in the mobile phase:

b) Fraction of time spent in the mobile phase $t_{m}$ would be

$\frac{t_{m}}{t_{m} + t_{s}} k = \frac{t_{s}}{t_{m}} t_{s} = k 脳 t_{m}$

Substitute the expression

$鈬� \frac{t_{m}}{t_{m} + t_{s}} 鈬� \frac{t_{m}}{t_{m} + k 脳 t_{m}} 鈬� \frac{t_{m}}{t_{m} + k 脳 t_{m}} \frac{1}{1 + k 脳 1} \frac{1}{1 + k}$

04

To find the retention Factor in chromatography:

c) The retention ration in chromatography is defined as

$R = \frac{time for solvent}{time for solute to pass through} R = \frac{t_{m}}{t_{r}} R = \frac{t_{m}}{t_{m} + t_{s}} R = \frac{1}{1 + k}$

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Most popular questions from this chapter

This problem reviews concepts from Chapter 23 using

Figure 24-15.

(a) Calculate the retention factor for peak 11 given tm 5 6.7 min.

(b) Calculate the number of theoretical plates (N in Equation 23-31)

and the plate height (H) for peak 11.

(c) Find the resolution (Equation 23-23) between peaks 16 and 17.

(a) When would you use split, split less, or on-column injection in gas chromatography?

(b) Explain how solvent trapping and cold trapping work in split less injection.

Heptane, decane, and an unknown had adjusted retention times of $12.6 \min$ (heptane), $22.9 \min$ (decane), and $20.0 \min$ (unknown). The retention indexes for heptane and decane are 700 and 1000 , respectively. Find the retention index for the unknown.

Genotoxic compounds damage DNA and cause mutations or cancer.Regulatory guidelines limit genotoxic impurities in pharmaceuticals. Mesityl oxide (4-methyl- 3-penten-2-one) is an intermediate product in the synthesis of some drugs. Search the literature for a gas chromatography method for the determination of mesityl oxide in the pharmaceutical enalapril maleate 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 is the instrumental method used?

(c) What type of column was used?

(d) What quantification method is used?

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

(f) For how long could a standard solution be used?

This problem reviews concepts from Chapter 23. An unretained solute passes through a chromatography column in 3.7 min and analyte requires 8.4 min.

(a) Find the adjusted retention time and retention factor for the analyte.

(b) Find the phase ratio b for a 0.32-mm-diameter column with a 1.0-mm-thick film of stationary phase.

(c) Find the partition coefficient for the analyte.

(d) Determine the retention time on a similar length of 0.32-mm diameter column with a 0.5-mm-thick film of the same stationary phase at the same temperature.

See all solutions

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