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D C Stahl

Publications and source records attributed to D C Stahl.

8 recordsLinked to original sources
PubMed2001

Screening method for nitroaromatic compounds in water based on solid-phase microextraction and infrared spectroscopy.

A new method is described for determining nitroaromatic compounds in water that combines solid-phase microextraction (SPME) and infrared (IR) spectroscopy. In this method, the compounds are extracted from a 250-mL volume of water into a small square (3.2 cm x 3.2 cm x 61.2 microm thick) of silicone polycarbonate copolymer film (MEM-213). Five nitroaromatic compounds, including 2,4,6-trinitrotoluene (TNT), were chosen to evaluate the SPME/IR procedure. Quantitation limits for the five test compounds range from 50 microg/L for TNT to 400 microg/L for nitrobenzene. Precision values, determined at aqueous concentrations of four times the quantitation limit, range from 4 to 7%, and linear dynamic ranges extend to the maximum limit of the IR instrumentation. The potential of this SPME/IR method for determining nitroaromatics in natural water samples was also investigated by extracting "real world" soil samples contaminated with TNT. Results obtained from the SPME/ IR determination of the diluted extracts were in reasonable agreement with those obtained from dichloromethane extraction followed by gas chromatographic analysis.

Chromatography, Gas↗
PubMed1999

Liquid chromatography/microspray mass spectrometry for bacterial investigations.

Cellular proteins (biomarkers) specific to any individual microorganism, determined by the direct mass spectral analysis of the corresponding intact cellular suspension, can be applied for the rapid and specific identification of the organisms present in unknown samples. The components of the bacterial suspensions, after a rapid separation over a C18 reversed-phase microcapillary column, were directly subjected to on-line electrospray ionization followed by analysis using an ion trap tandem mass spectrometer. This approach is equally effective for gram-positive as well as gram-negative bacteria but has a distinct advantage over our earlier reported method involving matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). During electrospray ionitation mass spectrometry (ESI-MS), liquid samples can be directly analyzed and there is the potential for developing tandem mass spectral methods for more specific identification of the individual organisms present in crude bacterial mixtures. The total analysis time leading to unambiguous bacterial identification in samples was less than 10 minutes and the results were quite reproducible. Miniaturization of the instrumentation along with total automation of this simple process could have immense impact on field operations. Routine, rapid, cost-effective field monitoring of environmental samples, agricultural products, samples from food processing, industrial sites and health institutions for suspected bacterial contamination could be a reality in the near future. Potential utility in biological, medical, bioprocessing, pharmaceutical, and other industrial research is also enormous.

Bacillus anthracis↗
PubMed1996

Poly(rC) binding protein 2 binds to stem-loop IV of the poliovirus RNA 5' noncoding region: identification by automated liquid chromatography-tandem mass spectrometry.

The 5' noncoding region of poliovirus RNA contains an internal ribosome entry site (IRES) for cap-independent initiation of translation. Utilization of the IRES requires the participation of one or more cellular proteins that mediate events in the translation initiation reaction, but whose biochemical roles have not been defined. In this report, we identify a cellular RNA binding protein isolated from the ribosomal salt wash of uninfected HeLa cells that specifically binds to stem-loop IV, a domain located in the central part of the poliovirus IRES. The protein was isolated by specific RNA affinity chromatography, and 55% of its sequence was determined by automated liquid chromatography-tandem mass spectrometry. The sequence obtained matched that of poly(rC) binding protein 2 (PCBP2), previously identified as an RNA binding protein from human cells. PCBP2, as well as a related protein, PCBP1, was over-expressed in Escherichia coli after cloning the cDNAs into an expression plasmid to produce a histidine-tagged fusion protein. Specific interaction between recombinant PCBP2 and poliovirus stem-loop IV was demonstrated by RNA mobility shift analysis. The closely related PCBP1 showed no stable interaction with the RNA. Stem-loop IV RNA containing a three nucleotide insertion that abrogates translation activity and virus viability was unable to bind PCBP2.

Amino Acid Sequence↗
PubMed1995

A microscale electrospray interface for on-line, capillary liquid chromatography/tandem mass spectrometry of complex peptide mixtures.

A microcapillary liquid chromatography (HPLC) system designed for the gradient elution of peptide and protein samples at flow rates < 1 microL/min has been coupled to a triple-sector quadrupole mass spectrometer via a simple sheathless electrospray interface (microspray). The microspray interface used a flame-drawn, uncoated, fused silica needle with tip outer diameters in the range of 15-20 microm and an opening less than 5 microm in diameter. Online sample filtration to prevent clogging of the drawn needle was accomplished by using a hydrophilic PVDF membrane filter integrated into the needle assembly. The spray potential (0.5-1 kV) was applied directly to the sample stream through the capillary union. Stable electrospray conditions were obtained over the full range of the gradient (0-90% acetonitrile in water) and was generally independent of flow rate. Both off-line and online analyses of proteins and peptide digest mixtures were performed at sample levels less than 10 fmol. HPLC parameters could be optimized for either rapid LC/MS analysis or enhanced performance in LC/MS/MS experiments by modulation of the eluting peak widths. Additionally, flow could be greatly reduced as selected components pass through the interface to prolong the time available to collect mass spectral data. The reduced spectral background and peak width manipulation facilitated the acquisition of peptide production spectra (MS/MS) using real-time, automated instrument control procedures.

Chromatography, High Pressure Liquid↗
PubMed1993

The use of hydrogen-deuterium exchange to facilitate peptide sequencing by electrospray tandem mass spectrometry.

The utility of hydrogen-deuterium exchange for sequencing peptides by mass spectrometry is demonstrated. The number of exchangeable hydrogens in a peptide is readily obtained by electrospray analysis of the peptide dissolved in deuterated solvents. This information can be used, in conjunction with published computer algorithms for interpreting peptide mass spectra, to reduce significantly the number of candidate sequences that fit the experimental data. This information, when combined with fragment-ion information in the mass spectrum, greatly increases the reliability of sequence determination.

Amino Acid Sequence↗
PubMed1987

The effects of amphetamine-like designer drugs on monoaminergic systems in rat brain.

The response of brain dopaminergic and serotonergic systems to the amphetamine-like designer drugs, 3,4-methylenedioxyamp amphetamine (MDA) and 3,4-methylenedioxymethamphetamine (MDMA), was investigated and compared to methamphetamine (METH). Like METH, single or multiple doses of either drug caused marked reductions in both tryptophan hydroxylase (TPH) activity and concentrations of 5-hydroxytryptamine (5HT) and 5-hydroxyindoleacetic acid (5HIAA) in several brain regions. The reduction in 5HT content corresponded to the depression of TPH activity in all regions examined. In contrast to METH, which induced pronounced deficits in dopaminergic neuronal markers, repeated doses of MDA or MDMA did not alter striatal tyrosine hydroxylase (TH) activities or reduce striatal dopamine concentrations. A single dose of MDA or MDMA significantly elevated striatal dopamine content; however, after repeated drug administrations dopamine concentrations were comparable to control values. The effects of MDA or MDMA administration in the rat brain are reminiscent of those elicited by p-chloroamphetamine, a presumed serotonergic neurotoxin.

3,4-Methylenedioxyamphetamine↗
PubMed1986

The effects of 3,4-methylenedioxymethamphetamine (MDMA) and 3,4-methylenedioxyamphetamine (MDA) on monoaminergic systems in the rat brain.

The effects of two amphetamine-like designer drugs, 3,4-methylenedioxyamphetamine (MDA) and 3,4-methylenedioxymethamphetamine (MDMA), on dopaminergic and serotonergic systems in the rat brain were investigated and compared to those of methamphetamine (METH). Like METH, single or multiple 10 mg/kg doses of either drug caused marked reductions in both tryptophan hydroxylase (TPH) activity and concentrations of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid, in several serotonergic nerve terminal regions. In all regions examined, the reduction in 5-HT content corresponded to the depression of TPH activity. Unlike multiple METH administrations, which induced pronounced deficits in dopaminergic neuronal markers, repeated doses of MDA or MDMA did not alter striatal tyrosine hydroxylase (TH) activities or reduce striatal dopamine concentrations. A single dose of MDA or MDMA significantly elevated striatal dopamine content; however, after repeated drug administrations dopamine concentrations were comparable to control values. At this time, striatal levels of homovanillic acid were significantly elevated suggesting that both drugs influence dopamine turnover. The effects of MDA or MDMA administration in the rat brain are reminiscent of those elicited by p-chloroamphetamine, a presumed serotonergic neurotoxin.

3,4-Dihydroxyphenylacetic Acid↗