Determination of licit and illicit drugs and metabolites in human sweat by liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometry screening method in sweat was developed for the simultaneous determination of three licit drugs (nicotine, paracetamol, and caffeine); four illicit drugs (cocaine, ketamine, 25I-NBOMe and methamphetamine) and two metabolites (benzoylecgonine and cotinine). Target drugs were liberated from sweat patches with pH 5 sodium acetate buffer and further purified by solid phase extraction (SPE) utilising Strata-X-Drug B cartridges. Optimal solvent constituents for SPE organic wash and elution were 70% v/v methanol in deionised water and 5% v/v ammonium hydroxide in methanol respectively. Chromatographic separation was achieved using a superficially porous particle C18 column with gradient elution, using (A) 0.1% formic acid in water and (B) acetonitrile as mobile phase constituents. Target drugs were identified using a combination of retention time, and the ion ratios for two precursor-product ion transitions for each analyte monitored in multiple reaction monitoring (MRM) mode. The method was linear for all target drugs from 1.0-150.0 ng mL-1 with corresponding limits of quantitation of 1.0 ng mL-1. Limits of detection were found to range from 0.1-0.6 ng per patch. The method was subsequently applied to the analysis of sweat samples from five male and four female participants aged 20-25 years. Sweat was collected from two areas (right forearm and left thigh) using protected layers of gauze. All eighteen patches tested positive for at least one target analyte. The results of this study not only show a multi-substance screening method was achieved but also that sweat patches can be used to indicate an individual's drug use. Therefore, they can provide an alternative non-invasive technique for forensic applications.

Accurate determination of the thermal variation of the aperture of step-index optical fibers

Thermal variations of the aperture of step-index optical fibers have been studied by measuring the transmitted power when a laser beam is launched with a variable incidence. For not too-long fibers only the rays launched with the higher incidence are affected. The variations of their transmittance have been accurately related to the refractive-index ones. Silicone clad silica fibers are sensitive to temperature because the silicone index varies much more the the silica index. On the contrary, due to a compensation phenomenon between index variations of core and cladding materials, PMMA core fibers have apertures that are nearly insensitive to temperature.

Accurate characterization of the transmittivity of largediameter multimode optical fibers

We describe an original technique that permits a specially accurate measurement of the variations of the transmittance of optical fibers vs the incidence of launched light. For large-diameter large-aperture fibers, which prefer light power transmission, the transmittance may be modeled using geometric optics. Taking into account the reflection losses at both ends, the core attenuation and a very weak lack of reflectivity at the core-cladding interface, good agreement is obtained between calculated variations and experimental results for the three kinds of fiber tested. The remaining difference has to be attributed to the mode coupling process which may be thus evaluated. The too high attenuation coefficient, which is attributed to the cladding to account for the losses at the core-cladding interface, characterizes in fact a thin perturbed layer where the materials contact. Thus, this method is a good means to evaluate separately the various processes contributing to the attenuation of open beams along the fibers and to determine which process should be worked on to improve the transmittance.