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Chapter 25: Q8P (page 707)

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?

Short Answer

Expert verified

UHPLC can provide exquisite resolution when run slowly on long columns.

how many particles placed side-by- side are equal to one theoretical plate.

N=5.55.(37.8s)2(2.3)2N=1500

4渭尘1.7渭尘=2.4

(a)N=1500;H=33渭尘;19.4particle/plate

b) 2.4particle/plate

Step by step solution

01

definition of plate calculated using the formula

a) The number of plates on column can be calculated using the formula

N=5.552.trw21/2

N=5.55.(37.8s)2(2.3)2N=1500

The plate height is:

H=LNH=50mm1500H=0.033mm=33渭尘

The number of particles that are equal to one theoretical plate is

33渭尘1.7渭尘=19.4particle/plate

02

theoretical plate

The number of particles that are placed side-by-side and equal to one theoretical plate is:

4渭尘1.7渭尘=2.4particle/plate

The column in task (a) is being run for maximum speed because it has higher plate height and number of particles. b

Hence,

(a)N=1500;H=33渭尘;19.4particle/plate

b) 2.4particle/plate

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Most popular questions from this chapter

A mixture of 14compounds was subjected to a reversed-phase gradient separation going from 5%to 100%acetonitrile with

a gradient time of 60min. The sample was injected at t =time. All peaks were eluted between 22and 50min.

(a) Is the mixture more suitable for isocratic or gradient elution?

(b) If the next run is a gradient, select the starting and ending %acetonitrile

and the gradient time.

(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 bonded stationary phase for the separation of optical isomers has the structure

To resolve the enantiomers of amines, alcohols, or thiols, the compounds are first derivatized with a nitroaromatic group that increases their interaction with the bonded phase and makes them observable with a spectrophotometric detector.

When the mixture is eluted with 20 vol% 2-propanol in hexane, the (R)-enantiomer is eluted before the (S)-enantiomer, with the following chromatographic parameters:

Resolution=螖迟rwav=7.7

Relative retention(伪)=4.53

k for (R)-isomer =1.35

tm=1.00min

wherewavis the average width of the two Gaussian peaks at their base.

(a) Findt1,t2andwawith units of minutes.

(b) The width of a peak at half-height isrole="math" localid="1663582749865" w1/2(Figure 23-9). If the plate number for cach peak is the same, findw1/2for each peak.

(c) The area of a Gaussian peak is1.064脳peakheight脳w1/2. Given that the areas under the two bands should be equal, find the relative peak heights(heightR//heightS).

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?

(a) use figure 25-28a select a tetrahydrofurn/water mobile phase strength of equivalent strength to 80%methanol.

(b)Describe how to prepare 1 L of this tetrahydrofurn mobile phase.

(c)what limitation would be imposed by the use tetrahydrofurn.
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