Criteria for opiate identification using liquid chromatography linked to tandem mass spectrometry: problems in routine practice.
BACKGROUND
Liquid chromatography linked to tandem mass spectrometry (LC/MS/MS) is being increasingly used for drug confirmation. At present, no official criteria exist for drug identification using this technique although the European Union (EU) criteria for compound identification have been adopted. These criteria are evaluated with respect to opiate confirmation by LC/MS/MS and problems highlighted.


METHODS
Urine samples screened positive for opiates by immunoassay were subjected to confirmation by LC/MS/MS using multiple reaction monitoring (MRM) and two separate buffer systems of pH 6.8 and 8.0, respectively. The EU criteria for compound identification were applied for confirmation of morphine, 6-monoacetylmorphine (6MAM), codeine and dihydrocodeine (DHC).


RESULTS
Using the pH 6.8 buffer, confirmation could be achieved for 84%, 94%, 96% and 95%, respectively, for samples demonstrating MRM chromatographic peaks at retention times for morphine, 6MAM, codeine and DHC. Failure to meet the EU criteria was mainly attributed to low signal-to-noise (S:N) ratios or excessively high drug concentrations. Isobaric interferences and poor chromatography were also contributing factors. The identification of morphine was considerably improved with chromatography at pH 8.0 owing to resolution of interferences. Oxycodone metabolites were a potential problem for the identification of DHC.


CONCLUSIONS
Isobaric interferences can pose a problem with drug identification using LC/MS/MS. Optimizing chromatographic conditions is important to overcome these interferences. Consideration needs to be given to investigating drug metabolites as well as parent drugs in method development.
Fox
Elizabeth J
EJ
Department of Clinical Biochemistry, Leeds Teaching Hospitals NHS Trust, Britannia House, Morley, Leeds LS27 0DQ, UK. Elizabeth.Fox@leedsth.nhs.uk
Twigger
Shirley
S
Allen
Keith R
KR
D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003061:Codeine / Q000031:analogs & derivatives / Q000652:urine; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009022:Morphine Derivatives / Q000652:urine; D010098:Oxycodone / Q000652:urine; D015203:Reproducibility of Results; D053719:Tandem Mass Spectrometry / Q000379:methods*
D009022:Morphine Derivatives; D010098:Oxycodone; C026979:6-O-monoacetylmorphine; C014481:dihydrocodeine; D003061:Codeine