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Chapter 25: Q33P (page 710)

(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.

Short Answer

Expert verified

a) 53%

b)To prepare 1 L of this tetrahydrofuran mobile phase (53 %), we need to mix 530 mL of tetrahydrofuran with 470 mL of water.

c) The limitations that would be imposed by the use of tetrahydrofuran is that it absorbs UV radiation and attacks polyether, ether, ketone and plastic components.

Step by step solution

01

Definition of water mobile phase of equivalent strength

The weak solvent is commonly referred to as the A-solvent (percent A), and the strong solvent is referred to as the B-solvent ( percent B). The mobile phase is typically a mixture of A- and B-solvents, such as 40% buffer and 60% methanol (abbreviated 60 percent B).

a) Figure 25-28 depicts a nomograph of the volume percentage of solvents with the same eluent strength.

At the same eluent strength, a vertical line intersects each solvent line.

Tetrahydrofurn mobile phase

b) The figure shows that 53 percent of the tetrahydrofuran/water mobile phase strength is equivalent to a concentration of 80% methanol.

To prepare 1 L of this tetrahydrofuran mobile phase (53%), we need to mix 530 mL of tetrahydrofuran with 470 mL of water.

02

Limitations of tetrahydrofuran

c) The limitations that would be imposed by the use of tetrahydrofuran is that it absorbs UV radiation and attacks polyether, ether, ketone and plastic components.

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Most popular questions from this chapter

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 50×2.1mmc18UHPLC 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 many1.7μm diameter particles places placed dide-by are equal to one theoretical plate?

b) From figure25-3,we expect an optimum plate height of 4μm 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?

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

  2. If the retention time was 20mins on the 10.0μm particle size column, what is the retention time on the 5.0,3.0,or1.5μmcolumns 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 the10.0μmcolumn 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,or1.5μmcolumns form part (a)?

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

(a) Make a graph showing retention times of peaks 6, 7, and 8 in Figure 25-12 as a function of %acetonitrile (%B). Predict the retention time of peak 8 at 45% B.

(b) Linear-solvent-strength model: In Figure 25-12, tm = 2.7 min. Compute k for peaks 6, 7, and 8 as a function of %B. Make a graph of log k versus Φ, where Φ= %B/100. Find the equation of a straight line through a suitable linear range for peak 8. The slope is -S and the intercept is log kw. From the line, predict tr for peak 8 at 45% B and compare your answer with (a).

(c) Gradient elution: A linear eluent gradient from 40 to 80% acetonitrile over 30 min is performed on the column in Figure 25-12. Assuming a dwell volume of 0 mL, use your data from (b) to plot the retention factor of peaks 6 and 8 during the gradient. What are the general characteristics of the plot?

(d) Why are the peaks in a gradient separation sharp?

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=Δtrwav=7.7

Relative retention(α)=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×peakheight×w1/2. Given that the areas under the two bands should be equal, find the relative peak heights(heightR//heightS).

Question:The graph shows retention data from aC8silica column with an acetonitrile/water mobile phase.


(a) What mobile phase composition provides greatest retention(k)for the components? Least retention? Coelution (equalk)of two components?

(b) Predict the retention time of each peak at 40%and60%acetonitrite. Draw a chromatogram (a "stick diagram" representing each peak as a vertical line) of the separation at each mobile phase composition.

(c) Would60%acetonitrile yield adequate resolution?

(d) Assuming Gaussian peaks, does the separation at60%acetonitrile have the attributes of a good separation?
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