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Chapter 25: Q23P (page 709)

To which kinds of analytes do these liquid chromatography detectors respond?

(a) ultraviolet

(b) refractive index

(c) evaporative light scattering

(d) charged aerosol

(e) electrochemical

(f) fluorescence

(g) nitrogen chemiluminescence

(h) conductivity

Short Answer

Expert verified

The part (a), part (b), part (c), part (d), part (e), part (f), part (g), part (h) is

  1. Wavelengths below 210
  2. Its detection limit is about poorer than that of the ultraviolet detector
  3. significantly less volatile than the mobile phase
  4. Itsnearly equal response to equal masses of non-volatile analytes
  5. Chromatography detector responds to analytes that can be oxidized or reduced
  6. Chromatography detector responds only to the few analytes that fluoresce
  7. Chromatography detector responds to the molecules with N atom
  8. Chromatography detector responds ionic or ionizable compounds

Step by step solution

01

Ultraviolet

Part (a)

The ultraviolet liquid chromatography detector is selective for compounds with wavelengths above 210 nm and is universal for compounds with wavelengths below 210.

02

Refractive index

Part (b)

The refractive index liquid chromatography detector responds to almost every solute, but its detection limit is about poorer than that of the ultraviolet detector.

03

Evaporative light scattering

Part (c)

The evaporative light scattering liquid chromatography detector responds to any analyte that is significantly less volatile than the mobile phase.

04

Charged aerosol

Part (d)

The charged aerosol liquid chromatography detector is almost universal detector with nearly equal response to equal masses of non-volatile analytes.

05

Electrochemical

Part (e)

The electrochemical liquid chromatography detector responds to analytes that can be oxidized or reduced (for example it can be phenols, aromatic amines).

06

Fluorescence

Part (f)

The fluorescence liquid chromatography detector responds only to the few analytes that fluoresce.

07

Nitrogen chemiluminescence

Part (g)

The nitrogen chemiluminescence liquid chromatography detector responds to the molecules with N atom.

08

Conductivity

Part (h)

The conductivity liquid chromatography detector responds ionic or ionizable compounds.

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Most popular questions from this chapter

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?

  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?

The chromatogram in Box 25-3 shows the supercritical fluid chromatography separation of seven steroids monitored by three detectors.

(a) In the middle chromatogram, ultraviolet detection provides near universal response for the steroids, whereas in the lower chromatogram the ultraviolet detector provides a selective response for a few of the steroids. How can ultraviolet detection act as either a selective or universal detector?

(b) Why is a sloping baseline observed at 210 nm, but the baseline is flat at 254 nm?

(c) Use the baseline disturbance early in the 254 nm chromatogram to measure tm. How does the measured value compare with that predicted using Equation 25-5 given that the column is 25 脳 0.46 cm and the flow rate is 2.0 mL/min.

(a) List ways in which the resolution between two closely spaced peaks might be changed.

(b) After optimization of an isocratic elution with several solvents, the resolution of two peaks is 1.2How might you improve the resolution without changing solvents or the kind of stationary phase?

After poisonous melamine and cyanuric acid appeared in milk in China (Box11-3) in 2008, there was a flurry of activity to develop methods to measure these substances. An analytical method for milk is to treat 1volume of milk with 9 volumes of H2O2CH3CN(20:80vol/vol)to precipitate proteins. The mixture is centrifuged for 5minto remove precipitate. The supernatant liquid is filtered through a 0.5-渭尘filter and injected into a HILIC liquid chromatography column (TSK gel Amide-stationary phase) and products are measured by mass spectrometry with selected reaction monitoring (Section 22-5). Melamine is measured in positive ion mode with the transition尘/锄127鈫�85. Cyanuric acid is measured in negative ion mode with the transition m/2128鈫�42.

(a) Write the formulas for the four ions and propose structures for all four ions.

(b) Even though milk is a complex substance, only one clean peak is observed for melamine and one for cyanuric acid spiked into milk. Explain why
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