Comparison Of Infrared And Mass Spectroscopies For Drug Analysis

Forensic drug testing requires high confidence of identification and low limits of detection. Mass spectroscopy combined with gas chromatography (GC/MS) has typically been the analytical method of choice. To increase the detection capabilities, selected ion monitoring (SIM) has been employed with electron impact (EI) quadrupole MS instruments. This leads to a lower confidence of identification, inasmuch as the full scan is lost. Due to these limitations, alternate mass spectroscopy methods and infrared methods have been explored. Ion trap mass spectrometry reportedly provides the full scan information needed for identification at lower detection limits than full scan quadrupole MS. Methods employing gas chromatography Fourier transform infrared (GC/Fr-IR) spectroscopy provide absolute identification through infrared fingerprinting with routine detection in the parts per billion range. New developments in cryogenic sample deposition for GC/FT-IR have increased the sensitivity of the technique 100 to 1000-fold to match or surpass that of GC/MS. Vapor phase GC/FT-IR has been configured serially with quadrupole MS providing both identification processes with one GC injection, GC/IR/MS. GC/FT-IR methods for vapor phase and cryogenic deposition techniques have been developed for certain drugs and development is continuing for others.