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Chapter 25: Q40P (page 711)

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?

Short Answer

Expert verified

(a).The value of pH = 2.0 .

(b).pH鈮�4.0

(c).pH鈮�7.5

Step by step solution

01

Find pH:

pH value will be best for separation of benzoic acid, 4-nitrophenol and 3 -methyl benzoic acid. To separate benzoic acid, 4 -nitrophenol and 3 -methyl benzoic acid pH2.0 is best. Because of that pH givesretention factor with in0.5鈮�k鈮�20.

So the pH is 2.0.

02

Find pH:

pH value is the best for separation of benzoic acid, 4-methylaniline and 3 -methyl benzoicacid.To separate benzoic acid, 4 -methylaniline and 3 -methyl benzoic acid pH approximately 4 is the best.

So the pH is 4.0.

03

Find pH:

pH value will be best for separation of 4-nitrophenol, 4-methylaniline and codeine on a typical C18 silica column. To separate 4-nitrophenol, 4-methylaniline and codeine on a typical C18silica column pH approximately 7.5 is best. So the pH is 7.5.

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Most popular questions from this chapter

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

Why are silica stationary phase height limited to operating in the pH range 2-8?why does the silica in figure25-8have improved stability at low pH?

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.

Retention factors for three solutes separated on aC8non-polar stationary phase are listed in the table. Eluent was a 70 : 30 (vol/vol) mixture of 50 mM citrate buffer (adjusted to pH withNH3) plus methanol. Draw the dominant species of each compound at each pH in the table and explain the behavior of the retention factors.

  1. Use equation 25-1to estimate the length of a column required to achieve1.0脳104plates if the stationary phase particles size is10.5,5.0,3.0,or1.5渭尘

  2. If the retention time was 20mins on the 10.0渭尘 particle size column, what is the retention time on the 5.0,3.0,or1.5渭尘columns from part (a)? Assume that flow rate is constant for all columns.

  3. Use equation25-2to estimate the pressure of the column in (a) given that the pressure of the10.0渭尘column was4.4Mpa

  4. If the flow rate was2.0mL/min , what is the baseline width for the peaks on 10.5,5.0,3.0,or1.5渭尘columns form part (a)?

  5. Which of these column configurations would require a UHPLC instrument?
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