1. There are many similarities between the analytical techniques of gas chromato

Question

1. There are many similarities between the analytical techniques of gas chromatography (GC) and HPLC.

a. Write down the van Deemter Equation and explain the significance of each of the terms.

b. Explain why helium is a common carrier gas, even though hydrogen has a larger mean square molecular velocity.

c. Compare and contrast the sensitivities of a thermal conductivity detector and a flame ionization detector.

d. Suggest three ways that can readily be used to detect materials eluting from an HPLC column.

Explanation / Answer

a)
  van Deemter Equation

Height Equivalent to a Theoretical Plate, or HETP

HETP = A + (B / u) + Cu

Where:

b) Helium is most commonly used because it is safer than, but comprable to hydrogen in efficiency, has a larger range of flow rates and is compatible with many detectors.

c)

as thermal conductivity detectorCTCD) is less sensitive than the flame ionization detector (FID) and has a larger dead volume it will not provide as good resolution as the FID.

. The TCD is not as sensitive as other detectors but it is non-specific and non-destructive

The TCD is also used in the analysis of permanent gases (argon, oxygen, nitrogen, carbon dioxide) because it responds to all these pure substances unlike the FID which cannot detect compounds which do not contain carbon-hydrogen bonds.

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