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Chapter 25: Q10P (page 707)

Question: How do additives such as trienthylamine reduce tailing of certain solutes?

Short Answer

Expert verified

Additives such as trienthylamine reduce tailing of certain solutes.

They are used to mask free silanol groups.which improves peak shape by masking adsorption sites. Solutes are strongly bound to additives, which reduces tailing. Solutes are held strongly to additives which reduces their tailing.

Step by step solution

01

definition of silanol

Silanols have been used as nucleophilic partners in transition-metal catalysed carbon–carbon cross-coupling reactions, organocatalysts for carbonyl compound activation reactions, intramolecular guiding groups for C–H bond activation reactions, enzyme inhibitors, and bioactive compound isosteres.

They are used to mask free silanol groups.

which improves peak shape by masking adsorption sites.

Solutes are strongly bound to additives, which reduces tailing.

02

strongly additives

Solutes are held strongly to additives which reduces their tailing.

Hence,

They are used to mask free silanol groups which improves peak shape by masking adsorption sites. Solutes are strongly bound to additives, which reduces tailing. Solutes are held strongly to additives which reduces their tailing.

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Most popular questions from this chapter

Chromatography–mass spectrometry. HPLC separation of

enantiomers of the drug Ritalin on a chiral stationary phase was

shown in Problem 25-13.

(a) Detection is by atmospheric pressure chemical ionization with

selected reaction monitoring of the m/z 23484 transitions. Explain

how this detection works and propose structures for m/z 234 and m/z 84.

(b) For quantitative analysis, the internal standardH32-Ritalin with

a deuterated methyl group was added. Deuterated enantiomers have

the same retention times as unlabelled enantiomers. Which selected

reaction monitoring transition should be monitored to produce a

chromatogram of the internal standard in which unlabelled Ritalin

will be invisible?

Question: what are the general steps in developing an isocratic separation for reversed-phase chromatography?

Question:The graph shows retention data from aC8silica column with an acetonitrile/water mobile phase.


(a) What mobile phase composition provides greatest retention(k)for the components? Least retention? Coelution (equalk)of two components?

(b) Predict the retention time of each peak at 40%and60%acetonitrite. Draw a chromatogram (a "stick diagram" representing each peak as a vertical line) of the separation at each mobile phase composition.

(c) Would60%acetonitrile yield adequate resolution?

(d) Assuming Gaussian peaks, does the separation at60%acetonitrile have the attributes of a good separation?

HPLC peak should generally not have an asymmetry factor, B/A in figure 23-14,outside the range0.9-1.5

  1. Sketch the shape of a peak with an asymmetry of 1.8
  2. What might you do to correct the asymmetry?

Two peaks emerge from a reversed-phase chromatography column as sketched in the illustration.

According to Equation 23-33, resolution is given by

Resolution=N4(α-1)α(k21+k2)

where Nis plate number, αis relative retention (Equation23-20), and k2 is the retention factor for the more retained component (Equation 23-16).

(a) If you decrease the amount of organic solvent in the mobile phase, you will increase retention. Sketch the chromatogram if retention factors increase but Nand αare constant.

(b) If you change the solvent type or the stationary phase, you will change the relative retention. Sketch the chromatogram ifαincreases but Nandk1are constant.

(c) If you decrease particle size or increase column length, you can increase the plate number. Sketch the chromatogram if Nincreases by (i) decreasing particle size and (ii) increasing column length. Assume αand k2are constant.
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