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Chapter 25: Q20P (page 709)

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脳104M-1cm-1has a height h=128mm and a half-width w1/2=10.1mm. Compound B E254=168脳104M-1cm-1has w1/2=7.6mm. What is the height of peak B in millimeters?

Short Answer

Expert verified

The height of peak B in millimetershB=126.45mm

Step by step solution

01

Step 1:

Since the sample containing equal moles of compounds A and B, the peak Ares are proportional to molar absorptivity:

PeakApeakB=2.26.1041.68.104=1.064.hA.w1/21.064.hB.w1/2

02

Step 2:

The height of peak B is:

hB=1.064.hA.w1/2.1.68.1041.064.w1/2.2.26.104hB=1.064.128mm.10.1mm.1.68.1041.064.76mm.2.26.104hB=126.45mmHere,thefinalresultishB=126.45mm

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Most popular questions from this chapter

The figure shows the separation of two enantiomers on a chiral stationary phase.


Sepation of enantiomers of Ritalin by HPLC with a chiral stationary phase.[Data from R.Bakhitar,L.Ramos,and F.L.S.Tse, 鈥淨uantification of methlylphenidate in plasma using chiral Liquid-chromatography/Tandem mass spectrometry: Application to Toxicokinetric studies,鈥滱nal Chim Acta 2002,469,261.]

(a)From trandw1/2 find N for each peak.

(b) Fromtrandw1/2find the resolution.

(c)Giventm=1.62min, use Equation23-23with the average N to predict the resolution.

(a). Sketch a graph of the van Deemnter equation (plate height versus linear flow rate).what would the curve look like if the multiple path term were 0? If the longtitundinal diffusinal diffusion term were 0?

(b). Explain why the van Deemter curve for 1.8渭尘particles in figure 25-3is nearly flat at high flow rate.what can you say about each of the terms in the van Deemeter equation for 1.8渭尘particles.

(c). Explain why the 2.7渭尘superficially porous particle enables separations similar to those achieved by 1.8渭尘totally porous particles,but the superficially porous particle requires lower pressure.

(a) Nonpolar aromatic compounds were separated by HPLC on an octadecyl(C18)bonded phase. The eluent was 65 vol% methanol in water. How would the retention times be affected if 90% methanol were used instead?

(b) Octanoic acid and 1-aminooctane were passed through the same column described in (a), using an eluent of 20% methanol/80% buffer (pH 3.0). State which compound is expected to be eluted first and why.

role="math" localid="1656416023291" CH3CH2CH2CH2CH2CH2CH2CO2HOctanoicacidCH3CH2CH2CH2CH2CH2CH2CH2NH21鈥�Aminooctane

(c) Polar solutes were separated by hydrophilic interaction chromatography (HILIC) with a strongly polar bonded phase. How would retention times be affected if eluent were changed from 80 vol% to 90 vol% acetonitrile in water?

(d) Polar solutes were separated by normal-phase chromatographyon bare silica using methyl t-butyl ether and 2-propanol solvent. How would retention times be affected if eluent were changed from 40 vol% to 60 vol% 2-propanol? (Hint: See Table 25-4.)

Use Figure 25-30 for the following questions:

(a) What pH would be best for the separation of benzoic acid, 4-nitrophenol, and 3-methylbenzoic acid?

(b) What pH would be best for the separation of benzoic acid, 3-methylbenzoic acid, and 4-methylaniline?

(c) What pH would be best for separation of 4-nitrophenol, 4-methylaniline, and codeine on a typical C18-silica column?

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

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