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Chapter 25: Q6P (page 707)

a. Why are HPLC particles porous?

b. Why are the particles with60-120A掳pores used for small molecules but wide pore300-A掳stationary phases used to separate polypeptides and proteins?s

Short Answer

Expert verified

The porous HPLC particles increase the surface area, resulting in greater sample capacity.

Smaller pore stationary phases are used for small molecules, but wide pore stationary phases are used to separate polypeptides and proteins because the pores must be large enough for the dissolved substances to enter. Larger pores take up more surface area, so they should be avoided if possible.

Step by step solution

01

Step 1:Explanation

For part a, Because porous HPLC particles increase surface area, they have a higher sample capacity.

02

Explanation

For part b, Smaller pore stationary phases are used to separate small molecules, whereas wide pore stationary phases are used to separate polypeptides and proteins because the pores must be large enough for the dissolved substances to enter. Because larger pores take up more surface area, they should be avoided if possible.

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Most popular questions from this chapter

use figure 25-17to suggest which type of liquid chromatography you could use to separate compounds in each of the following categories.

(a)Molecular mass <2000,soluble in octane

(b) Molecular mass <2000 ,soluble in methanol-water mixtures

(c) Molecular mass <2000 ,weak acid

(d)Molecular mass<2000 ,soluble highly polar

(e) Molecular mass <2000 ,ionic

(f)Molecular mass<2000,soluble in water in nonionic various

(g) Molecular mass<2000,soluble in water in water, variety of changes

(h) Molecular mass<2000,soluble in tetrahydrofuran

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) 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.)

a) UHPLC can provide exquisite resolution when run slowly on long columns or rapid separation with reasonaple resolution if short columns are run fast. the drug acetaminophern run on a 50脳2.1mmc18UHPLC column has a retention time of 0.63min and a width at half-height of 2.3s.Find the plate number and plate height. How many1.7渭尘 diameter particles places placed dide-by are equal to one theoretical plate?

b) From figure25-3,we expect an optimum plate height of 4渭尘 how many particles placed side-by- side are equal to one theroretical plate? Do you think the column in (a) is being run for maximum resolution or maximum speed?

A known mixture of compounds A and B gave the following HPLC results:

A solution was prepared by mixing 12.49mgof Bplus 10.00mLof unknown containing just and diluting to 25.00mL. Peak areas of 5.97and 6.38were observed for AandB, respectively. Find the concentration of A(mg/mL)in the unknown.
See all solutions

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