This study has shown the promise of sensitive LC-MS/MS method to support microdose pharmacokinetics and drug metabolism studies in human.

No abstract

An optical multichannel absorbance detection system suitable for micro-HPLC is described. The detection system includes a flow cell with detection volume of 30 nL and path length of 12 mm. A fiber optic spectrometer with charge-coupled device array is used to collect spectral information at 1 Hz frequency. Signal-to-noise ratios are enhanced through the use of large bandwidth total absorbance signals, while linearity and spectral resolution are maintained. Theoretical predictions of bandwidth dependent signal-to-noise ratios of the total absorbance signal are compared to experimental observations, showing that optimum total absorbance signal bandwidths occur at 2.8 σabs for a Gaussian absorption band under light noise limited conditions. This bandwidth is much larger than bandwidths used in most commercial detectors. The detection system is applied to the separation of 2,4-dinitophenylhydrazones of organic carbonyls sampled from tropospheric air samples. For these hydrazones, a bandwidth of 181 nm is used for detection and calibration, which results in more universal hydrazone detection.

Based upon the well established method of derivitization with 2,4-dinitrophenylhydrazine, an instrument was developed for ambient measurement of carbonyls with significantly improved temporal resolution and detection limits through automation, direct injection, and continuous use of a single microsilica DNPH cartridge. Kinetic experiments indicate that the derivitization reaction on the cartridge is fast enough for continuous measurements with 50 min air sampling. Reaction efficiencies measured on the cartridge were 100% for the carbonyls tested, including formaldehyde, acetaldehyde, propanal, acetone, and benzaldehyde. Transmission of the carbonyls through an ozone scrubber (KI) were in the range of 97-101%. Blank levels and detection limits were lower than those obtainable with conventional DNPH methods by an order of magnitude or greater. Mixing ratio detection limits of carbonyls in ambient air were 38-73 ppt for a 50 min air sample (2.5 L). The instrument made continuous measurements of carbonyls on a 2 h cycle over a period of 10 days during a field study in southwestern Ontario. Median mixing ratios were 0.58 ppb formaldehyde; 0.29 ppb acetaldehyde; 1.14 ppb acetone; and 0.45 ppb glyoxal. Glyoxal shows a significant correlation with ozone and zero intercept, consistent with a secondary source and minor direct source to the atmosphere. The method should easily be extendable to the detection of other low molecular weight carbonyls that have been previously reported using the DNPH technique.

A method has been devised with the capacity to extend the linear dynamic range of a triple quadrupole mass spectrometer operated in the selected reaction monitoring (SRM) mode of analysis. This extended range experiment can be realized by simultaneously acquiring variably sensitive data, via collision energy adjustment, for the same precursor-to-product ion transition within a single SRM method. While this method can be applied universally to many different study types without any detrimental effect to the analysis or throughput, it was applied herein to acquire and quantify, within a single analysis, the concentrations of GSK-A in a multiple-dose rodent study, that previously required a dilution scheme. Using this methodology, the linear dynamic range of GSK-A was increased over traditional methods by nearly two orders of magnitude, from 2.00-10,000 ng/mL to 0.500-100,000 ng/mL.