Chromatography Part A Obj 4

Question 1

What are the 2 main categories of detectors?

Answer 1

Universal: respond to a physical change in the carrier gas and react to all types of sample molecules

Specific: respond to specific types of sample molecules

Question 2

What is the most common type of detector and how does it work?

Answer 2

Thermal Conductivity Detector (TCD), a universal detector that responds to the thermal conductivity of the carrier gas. When the carrier gas comes into the detector with a sample the thermal conductivity drops.

Question 3

What type of circuit design is used in the thermal conductivity detector?

Answer 3

Wheatstone bridge

Question 4

Describe Flame Ionization Detector.

Answer 4

Measures organic compound that ionize when burnt. The FID detects in the ppb range and does not work for inorganic compounds such as CO2 or water vapour as they do not ionize when burnt.

Question 5

Describe Flame Photometric Detectors.

Answer 5

A detector that is designed specifically for Sulfur detection. It can measure in ppb range and works by making Sulfur atoms emit light which in turn gets detected by a photomultiplier tube. The PMT produces a voltage proportional to the amount of Sulfur.

Question 6

Describe Photoionization detector.

Answer 6

The PID is used to detect heavier alkanes (five or more atoms) an aromatic molecules. It can detect in the ppb range and uses a UV lamp.