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Chapter 24: Q1TY (page 641)

Where would an unknown with a retention index of 936 be eluted in Figure 23-7?

Short Answer

Expert verified

The eluted unknown with a retention index of 936 would be found after nonane.

Step by step solution

01

Step 1: Concept used

Kovats retention index:

For linear alkanes, the retention index, I , equals 100times the number of carbon atoms.

For a molecule of Octane, I=800 calculated using the formula

I=100[n+N-nlogL'unknown-logL'nlog4N-log4'n]

where

n=number of carbon atoms in smaller alkane

N=number of carbon atoms in larger alkane

tr'(n)=adjusted retention time of smaller alkane

localid="1663581965257" tr'(N)=adjusted retention time of larger alkane.

02

Position of the unknown

Nonane has a retention value of 900, whereas the unknown has a retention index of 936. Therefore, the eluted unknown with a retention index of 936 would be found after nonane.

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Most popular questions from this chapter

Retention time depends on temperature, T, according to the equation log t鈥�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鈥�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鈥�r at 353K

(a) Use Trouton's rule, 鈭�Hvap掳鈮�(88Jmol-1K-1)Tbp, to estimate the enthalpy of vaporization of octane (b.p. 126掳).

(b) Use the form of the Clausius-Clapeyron equation below to estimate the vapor pressure of octane at the column temperature in Figure 24-9(70掳C)

In(P1P2)=-(鈭�HvapR)(1T1-1T2)

(c) Calculate the vapor pressure for hexane (b.p. 69掳C) at70掳C

(d) What is the relationship between solute vapor pressure and retention?

(e) Why is the technique called "gas chromatography鈥� if retained analytes are only partially vaporized?

(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.

To which kinds of analyses do the following gas chromatography detectors respond?

(a) thermal conductivity

(b) flame ionization

(c) electron capture

(d) flame photometric

(e) nitrogen-phosphorus

(f) photo ionization

(g) sulfur chemiluminescence

(h) atomic emission

(i) mass spectrometer

(j) vacuum ultraviolet

Why is split less injection used with purge and trap sample preparation?

See all solutions

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