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Chapter 25: Q2TY (page 696)

25-2Why does the retention onder of peaks 2 and 3 change on the polar embedded column?

Short Answer

Expert verified

Compound 2 has polar functionalities that could interact with the polar embedded groups, increasing retention. Compound 3 cannot interact with these groups

Step by step solution

01

Define interpretation

Interpretation:

The reason why the retention order of compound 2 and compound 3 changes on polar embedded column has to be explained..

Concept Introduction:

Retention of the compound depends upon the functional groups that are present in it and the column that is used for HPLC. If a polar column is used means the polar compounds gets attracted more and vice-versa.

02

Explanation

Compound 2 is 4-butylbenzoic acid and compound 3 is toluene. By looking into the two compounds, we find that compound 2 has a polar acid group, while compound 3 does not have polar groups. Therefore, when using polar embedded column for HPLC, compound 2 interacts more than compound 3 due to the presence of the polar acidic group. Compound 3 does not have any polar groups and this does not interact with the polar embedded column. Hence, the compound 2 has more retention compared to compound 3 . This is the reason why the retention order is changed in the polar embedded column.

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Most popular questions from this chapter

Suppose that an HPLC column produces Gaussian peaks. The detector measures absorbance at 254 nm. A sample containing equal moles of compounds A and B was injected into the column. Compound A E254=2.26×104M-1cm-1has a height h=128mm and a half-width w1/2=10.1mm. Compound B E254=168×104M-1cm-1has w1/2=7.6mm. What is the height of peak B in millimeters?

what is the difference between extra-column volume and dwell volume? How do each of these volumes affect a chromatogram?

After poisonous melamine and cyanuric acid appeared in milk in China (Box11-3) in 2008, there was a flurry of activity to develop methods to measure these substances. An analytical method for milk is to treat 1volume of milk with 9 volumes of H2O2CH3CN(20:80vol/vol)to precipitate proteins. The mixture is centrifuged for 5minto remove precipitate. The supernatant liquid is filtered through a 0.5-μmfilter and injected into a HILIC liquid chromatography column (TSK gel Amide-stationary phase) and products are measured by mass spectrometry with selected reaction monitoring (Section 22-5). Melamine is measured in positive ion mode with the transitionm/z127→85. Cyanuric acid is measured in negative ion mode with the transition m/2128→42.

(a) Write the formulas for the four ions and propose structures for all four ions.

(b) Even though milk is a complex substance, only one clean peak is observed for melamine and one for cyanuric acid spiked into milk. Explain why

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(a) In the middle chromatogram, ultraviolet detection provides near universal response for the steroids, whereas in the lower chromatogram the ultraviolet detector provides a selective response for a few of the steroids. How can ultraviolet detection act as either a selective or universal detector?

(b) Why is a sloping baseline observed at 210 nm, but the baseline is flat at 254 nm?

(c) Use the baseline disturbance early in the 254 nm chromatogram to measure tm. How does the measured value compare with that predicted using Equation 25-5 given that the column is 25 × 0.46 cm and the flow rate is 2.0 mL/min.

Microporous silica particles with a density of2.2g/mLand a diameter10μmof have a measured surface area of calculated the surface area of the300m2spherical silica as if it were simply solid particles what does this calculation tell you about the shape or porosity of the particles.
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