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TitlePractice Problem Set Mixed Chromatography Questions
TagsChromatography Elution High Performance Liquid Chromatography Gas Chromatography Scientific Techniques
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Practice Problem Set 10Practice Problem Set 10

Mixed Chromatography ProblemsMixed Chromatography Problems

1. Use the following gas chromatogram of a mixture of dioxane and cyclohexane eluted on a1. Use the following gas chromatogram of a mixture of dioxane and cyclohexane eluted on a

non-polar column to answer the following two questions.non-polar column to answer the following two questions.

a. What is the identity of the substance labeled peak A? Expa. What is the identity of the substance labeled peak A? Explain how you deduced this.lain how you deduced this.

 peak A = dioxane, peak A = dioxane,

explanation: since it is more polar and explanation: since it is more polar and thus will elute early on a nonpolar stationary phasethus will elute early on a nonpolar stationary phase

 b. The  b. The area measured area measured for peak for peak A is A is 2 c2 cmm
22
 and the area measured for peak B is 3 cm and the area measured for peak B is 3 cm

22
. Assuming. Assuming

that the detector response is the same for both substances, calculate the mol% of A in thethat the detector response is the same for both substances, calculate the mol% of A in the

mixture.mixture.

mol% A mol% A = = 2/5 = 2/5 = 40%40%

2. You are given a sample composed of three compounds, A-C with different polarities. The2. You are given a sample composed of three compounds, A-C with different polarities. The

sample is loaded onto a Csample is loaded onto a C1818 column and eluted with 30% methanol/water mp. After eluting with column and eluted with 30% methanol/water mp. After eluting with

10 mL of solvent and collecting 1 mL fractions, compounds A and B are found to be in the 3rd10 mL of solvent and collecting 1 mL fractions, compounds A and B are found to be in the 3rd

and 6th fractions, respectively.and 6th fractions, respectively.

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B. Decreased resolution due to band broadening

C. Non-linear detector response

D. Constant resolution

The GC graph obtained after an experiment is called a20.

A. chromatograph B. chromatogram

C. chromatophore D. graph

Which of the following detectors give concentration-dependent signals?21.

A. Electron-capture detector

B. Thermal conductivity

C. Infra-red detector

D. All of these

What useful information can be found from a Van Deemter plot?22.

A. The selectivity factor

B. Optimum mobile phase flow rate

C. Optimum column temperature

D. Optimum column length

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