1. GC/MS systems are widely used for measuring drugs of
abuse in urine toxicology confirmations
2. Drugs and metabolites must be extracted from body fluids
and typically reacted with derivatizing reagents to form compounds
that are more volatile for the GC process
3. Computerized libraries and matching algorithms are available
within the instrument to compare mass spectral results of an unknown
substance obtained from a sample to the reference library
4. Increasingly, LC/MS (including LC/MS/MS) technology is taking
its place alongside GC/MS in clinical laboratories.
5. LC offers a number of advantage over GC
6. Typically, LC requires less extensive extraction procedures and
derivatization is rarely used, saving time and expense.
7. In Addition, polar and heat-labile compounds fare better in LC
8. However, the chromatography itself in LC can be somewhat less
robust than in GC, resulting in wider peaks, more variable retention
times and potentially requiring more frequent maintenance
9. Another disadvantage of LC/MS is the less reproducible mass
spectra, as mentioned earlier
10. Besides its use in toxicology, LC/MS also has great potential for
measuring low-level and mixed-polarity analytes such as vitamin D,
testosterone, and immuno-suppressant drugs due to its superior
sensitivity and specificity over immunoassays.
11. In addition, LC/MS has the advantage of being able to detect multiple
analytes (such as a panel of drugs or a series or metabolites) in one run
12. LC/MS is free from the antibody interferences seen in immunoassays,
althought LC/MS han its own type of interference in the form of ion supprssion
13. This effect is seen when a co-eluting chemical in the sample
prevents a compound of interest from being ionized, thereby reducing or
eliminating its signal
14. LC/MS also requires highly skilled operators and it not nearly as
automated as immunoassay instruments
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