/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Q38P (a) When you try separating an u... [FREE SOLUTION] | 91影视

91影视

Log out

Learning Materials

Features

Discover

Chapter 25: Q38P (page 711)

(a) When you try separating an unknown mixture byreversed-phase chromatography with 48%acetonitrile 50%water,the peaks are too close together and are eluted in the range k = 2- 6Should you use a higher or lower concentration of acetonitrile in thenext run?

(b) When you try separating an unknown mixture by normal-phasechromatography with 50%hexane50% methyl t-butyl ether, thepeaks are too close together and are eluted in the range k = 2 - 6Should you use a higher or lower concentration of hexane in thenext run?

Short Answer

Expert verified

(a) Lower concentration of acetonitrile should be used because lower solvent strength increases the difference in retention between compounds.

(b) Solvent that would lower the solvent strength is recommended for the use. In this case it is hexane.

Step by step solution

01

Define Acetonitrile:

Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula CH3CN. This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not classed as organic). It is produced mainly as abyproduct of acrylonitrile manufacture.

02

Concentration of Acetonitrile:

We should use lower concentration of acetonitrile because lower solvent strength increases the difference in retention between compounds.

01

DefineChromatography

Chromatography is a group of laboratory techniques used to separate the components of a mixture by passing the mixture through a stationary phase.

02

The Concentration of Hexane:

We should use a higher concentration of hexane in the next run because in normal-phase chromatography, solvent strength increases as the solvent becomes more polar (in this case methyl t-butyl ether is more polar). So, to improve resolution and increase the retention time,such solvent should be used that would lower the solvent strength. In this case it is hexane.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91影视!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

(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) 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?

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

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(伪-1)伪(k21+k2)

where Nis plate number, 伪is 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 伪are constant.

(b) If you change the solvent type or the stationary phase, you will change the relative retention. Sketch the chromatogram if伪increases 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 伪and k2are constant.

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?
See all solutions

Recommended explanations on Chemistry Textbooks

Physical Chemistry

Read Explanation

The Earths Atmosphere

Read Explanation

Chemical Analysis

Read Explanation

Ionic and Molecular Compounds

Read Explanation

Inorganic Chemistry

Read Explanation

Nuclear Chemistry

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.