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Other instrumental detection methods

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  p359-360

2026-11-03

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Other instrumental detection methods

Radioisotope-labelled drugs and their metabolites can be detected selectively with good sensitivity by imaging detectors that use windowless gas-flow proportional counters as detectors. The proportional counter is filled with a mixture of argon and methane gas, which is ionised locally by collision with beta or gamma rays produced by radioactive decay in the sample zones that contain radioisotopes. The local bursts of ionised gas molecules are sensed by a position-sensitive detector and stored in computer memory. These signals are accumulated for quantitative measurements.

Flame ionisation has been used to detect samples of low volatility that lack a chromophore for optical detection. The separation is performed on specially prepared, thin, quartz rods with a surface coating of sorbent attached by sintering. The rods are developed in the normal way, usually held in a support frame that also serves as the scan stage after the rods have been removed from the developing chamber and dried. The rods are moved at a controlled speed through a hydrogen flame and the signal is processed in a similar manner to that with the flame ionisation detector used in gas chromatography. The linear working range of the detector is about 3–30 lg for most substances. There are few reported applications in drug analysis. General interfaces are available for the in-situ measurement of mass, infrared and Raman spectra of separated zones on TLC plates. Individual results in terms of sensitivity and spectral quality are impressive, but none of these methods is used routinely in drug analysislaboratories. This is a possible area for development.