Increasing the efficiency of pharmacokinetic sample procurement, preparation and analysis by liquid chromatography/tandem mass spectrometry

The movement towards a 96-well format has greatly increased productivity and throughput in bioanalytical laboratories. Improvements in automated sample preparation and analytical methods have further contributed to increased productivity. We have focused on sample collection and transfer to the bioanalyst and have found improvements to the current available methods. The problem of manual transfers and plasma clotting issues can be overcome with the use of microtainers. Specifically, for illustrative purposes, three proprietary Theravance compounds were tested for stability, non-specific binding, and electrospray ion suppression in microtainers. There were no issues with stability, non-specific binding or ion suppression for the above compounds even after leaving plasma samples in the microtainers over long periods of time. The microtainers are robot-compatible and the resulting plasma can be transferred without clotting issues. To date, all in-house compounds successfully analyzed and tested using the microtainers have mass ranges between 200 and 1800 Da, pK(a) ranges between 3.8 and 10.3, and logD ranges between -1.7 and 4.2. Once samples are transferred into 96-well plates, flexibility in preparation and analysis is available. Together with automated sample preparation and the use of liquid chromatography/tandem mass spectrometry (LC/MS/MS) as an analytical tool, the use of microtainers as sample collection tubes and for sample storage saved considerable time, cost and effort in both of our pharmacokinetic (PK) and bioanalytical groups. This in turn has led to an increased efficiency and overall throughput in support of our drug discovery effort.     

Polymerase chain reaction technology as analytical tool in agricultural biotechnology

The agricultural biotechnology industry applies polymerase chain reaction (PCR) technology at numerous points in product development. Commodity and food companies as well as third-party diagnostic testing companies also rely on PCR technology for a number of purposes. The primary use of the technology is to verify the presence or absence of genetically modified (GM) material in a product or to quantify the amount of GM material present in a product. This article describes the fundamental elements of PCR analysis and its application to the testing of grains. The document highlights the many areas to which attention must be paid in order to produce reliable test results. These include sample preparation, method validation, choice of appropriate reference materials, and biological and instrumental sources of error. The article also discusses issues related to the analysis of different matrixes and the effect they may have on the accuracy of the PCR analytical results.     

On the formation, nature, stability and biological relevance of the primary reaction intermediates of myoglobins with hydrogen peroxide

The reaction between hydrogen peroxide and myoglobin (or haemoglobin) ferric haem is a two-electron redox process, yet the stable product is ferryl haem, retaining only one oxidizing equivalent. We have used SVD (singular value decomposition) and global spectroscopic analysis to examine the transient primary spectral intermediates in this reaction, which have been reported as either "compound 0"(ferric peroxide) or "compound I"(ferryl and porphyrin cation radical) types and which may precede the formation of ferrylmyoglobin. To test the hypothesis that the distal histidine facilitates ferryl formation we studied the myoglobin-like haemoglobin from the gastropod mollusc Aplysia fasciata, where this histidine is replaced by valine and its hydrogen bonding role is taken up by a non-homologous arginine. In this protein, consistent with the distal histidine hypothesis, a compound 0 intermediate is formed identified by an EPR spectrum typical of low spin ferric haem complexes. It is significantly more stable than any species seen with mammalian myoglobin. Thirdly, as ferryl haems and associated free radicals may play a role in disease, we have studied the action of myoglobin-peroxide mixtures towards external reductants. Even at a low pH, where ferrylmyoglobin is protonated and in its most reactive state, pre-incubation with reducing donors, including one-electron donors such as ferrocyanide, prior to peroxide addition renders both oxidizing equivalents available. The physiological antioxidant vitamin, ascorbate, is also able to trap both reactive species. Myoglobin can therefore act as a true ascorbate peroxidase. Ascorbate in vivo may be critical in controlling and preventing toxic side reactions of this and related haem proteins.     

Hydrophilic interaction liquid chromatography/electrospray mass spectrometry determination of acyclovir in pregnant rat plasma and tissues

Reversed-phase chromatography is the most common means of separation for small drug molecules. However, polar drugs may suffer from poor retention and peak shape in reversed-phase high-performance liquid chromatography (RP-HPLC). Hydrophilic interaction liquid chromatography (HILIC) provides a viable alternative to RP-HPLC and is an excellent way to separate polar compounds. This paper describes a HILIC/ESI-MS/MS assay for the determination of acyclovir from rat plasma, amniotic fluid, placental tissue, and fetal tissue. The isocratic separation utilizes an underivatized silica column with an acetonitrile/formate buffer mobile phase (80:20). The method is validated over a range of 50 ng/mL to 50 micro g/mL with % error and % relative standard deviation of <15% over 3 days. All samples are prepared by acetonitrile protein precipitation, which yields high recovery (>84% for acyclovir). This assay can be applied to the pharmacokinetic study of the placental transfer of acyclovir.     

On the restriction of Deligne-Lusztig characters

We study the multiplicities of Deligne-Lusztig characters upon restriction from a finite reductive group to a finite reductive subgroup. The result is a qualitative formula for the growth of multiplicities in terms of complexity. For restrictions from to we get exact multiplicities.

     

Development of a murre (<Emphasis Type="Italic">Uria</Emphasis> spp.) egg control material

The Seabird Tissue Archival and Monitoring Project (STAMP) is a collaborative Alaska-wide effort by the US Fish and Wildlife Service’s Alaska Maritime National Wildlife Refuge (USFWS/AMNWR), the US Geological Survey’s Biological Resources Division (USGS/BRD), the Bureau of Indian Affairs Alaska Region Subsistence Branch (BIA/ARSB), and the National Institute of Standards and Technology (NIST) to monitor long-term (decadal) trends in environmental contaminants using seabird eggs. To support this effort, a matrix- (seabird egg) and concentration-specific control material was needed to ensure quality during analytical work. Although a herring gull egg quality assurance (HGQA) material is available from Environment Canada (EC), contaminant concentrations in this material tended to be higher than those observed in Alaskan murre (Uria spp.) eggs. Therefore, to prepare a more appropriate control material, a total of 12 common murre (U. aalge) and thick-billed murre (U. lomvia) eggs from four Bering Sea and Gulf of Alaska nesting locations were cryohomogenized to create 190 aliquots each containing approximately 6 g. This new control material was analyzed by different methods at NIST and EC facilities for the determination of concentrations and value assignment of 63 polychlorinated biphenyl (PCB) congeners, 20 organochlorine pesticides, and 11 polybrominated diphenyl ether (PBDE) congeners. The total PCB concentration is approximately 58 ng g⁻¹ wet mass. Results obtained for analytes not listed on the certificates of analysis of the previously used control materials, HGQA and NIST’s Standard Reference Material (SRM) 1946 Lake Superior Fish Tissue, are also presented.      

Tandem mass spectrometry and hydrogen/deuterium exchange studies of protonated species of 1,1'-bis(diphenylphosphino)-ferrocene oxidative impurity generated during a Heck reaction

Oxidation of 1,1'-bis(diphenylphosphino)-ferrocene (DPPF) was found to occur when it served as the ligand for Pd(II)(CH3COO)2 in a Heck reaction. This oxidative impurity of DPPF, referred to as DPPF(O), was identified by high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) and exact mass measurements. Protonated DPPF(O) exhibited unique fragmentation pathways in the gas phase. Hydrogen/deuterium (H/D) exchange experiments provided important insights into the dissociation mechanisms of protonated DPPF(O), suggesting the existence of isomeric structures of the product ions by retaining or losing a proton (or deuteron) upon collision-induced dissociation (CID). The specific fate of the proton (or deuteron) upon CID is postulated to be dependent on the distance between the exchangeable proton (or deuteron) and the sites of bond cleavage. Density functional theory (DFT) calculations at the B3LYP/LANL2DZ level of theory showed that oxygen in DPPF(O) plays a pivotal role in invoking pi-cation interactions between the p-type lone pair electrons (n pi) in oxygen and the anti-bonding orbital of Fe(II), accounting for the major fragmentation pathways of protonated DPPF(O). Facile formation of organometallic distonic ions in dissociation of protonated DPPF(O), and especially of protonated DPPF, could be useful for further exploration of their chemical properties by gas-phase ion/molecule reactions.     

Formation of single-phase microemulsions in toluene/water/nonionic surfactant systems

Mixtures of toluene and water from 5 to 50% oil fraction and 5 to 25% surfactant by weight were studied. Winsor Type IV microemulsions were formed in numerous cases. Review of partial ternary phase diagrams for these systems indicated the area of single-phase microemulsion with toluene could be maximized at an hydrophilic-lipophilic balance (HLB) of approximately 14.5. Select single-phase samples were further analyzed by surface tension and dynamic light scattering techniques, which allowed a detailed characterization of the solution equilibrium thermodynamics and size stability. Particle sizes averaged approximately 5 nm and were nearly constant over a wide variety of conditions and for 6-18 months. When benzyl alcohol was used instead of toluene, the optimum HLB for the formation of single-phase systems was found to have a lower limit of 17. Particle sizes in these systems were <30 nm but showed greater variability. The decrease in particle size as surfactant concentration increased was determined to be associated with changes in ethlyene oxide chain conformation. The increase in particle size due to swelling with increased oil concentration was used to determine the surfactant surface area in the oil phase. A detailed comparison of alkylamine ethoxylate to octyl- and nonylphenol ethoxylate surfactants in terms of micelle thermodynamics, size, and stability indicate that the alkylamine-based surfactants are potential candidates for the replacement of nonylphenol-based surfactants in some systems with a more polar oil phase like benzyl alcohol.