Combination of high-performance liquid chromatography and SERS detection applied to the analysis of drugs in human blood and urine

Surface-enhanced Raman scattering (SERS) spectroscopy was employed to characterise different drugs and some of their degradation products contained in bio-matrices after separation by HPLC. Since acetonitrile, which is contained in the widely used Daldrup type eluents, adsorbs readily to the silver surface and disturbs SERS measurements at low analyte concentration, a gradient technique relying on a methanol/buffer mixture was developed. Application of this eluent helps to lower the detection limit of most of the drugs investigated (e.g. Dihydrocodeine, Doxepine, Citalopram, Trimipramine, Carbamazepine, Methadone) into the 1 mg/sample domain. The examples presented also demonstrate that the retention times determined by independent runs of reference solutions alone are not always sufficient for a unique identification of all fractions appearing in the chromatogram of a mixture that may contain degradation products. The Raman band patterns of many derivatives are, however, so distinct that in these cases an assignment to certain families of drugs is possible even without a detailed analysis of the spectrum (correlation of band positions with calculated normal mode frequencies). If SERS spectra of reference solutions recorded under similar experimental conditions are available, the described technique can provide a second, independent means of identification next to HPLC/MS for example if necessary during a law suit. q 2004 Elsevier B.V. All rights reserved