Biomedical subjects

Joseph H Aldstadt

Publications and source records attributed to Joseph H Aldstadt.

3 recordsLinked to original sources

PubMed2004

Sensitive method for the determination of roxarsone using solid-phase microextraction with multi-detector gas chromatography.

We describe the development, optimization, and application of a novel method for the unequivocal identification and quantification of roxarsone (3-nitro-4-hydroxyphenylarsonic acid, 3-NHPAA) at low microg L(-1) levels. The method is based on capillary gas-liquid chromatography with parallel quadrupole ion-trap mass spectrometric (QIT-MS) and pulsed flame photometric detection (PFPD). The sensitive method couples the arsenic specificity of PFPD with the high selectivity of molecular MS for the determination of roxarsone, dimethylarsenic acid (DMAA), and monomethylarsonic acid (MMAA) in complex matrices. Analytes were derivatized based on the approach we previously reported [B. Szostek, J.H. Aldstadt, J. Chromatogr. A 807 (1998) 253 and D.R. Killelea, J.H. Aldstadt, J. Chromatogr. A 918 (2001) 169] for the reaction of organoarsenicals with 1,3-propanedithiol (PDT). The cyclic dithiaarsenolines formed were extracted from the sample matrix in the liquid phase by solid-phase microextraction (SPME). The optimized SPME conditions employed a 65 microm polydimethlysiloxane-divinylbenzene (PDMS-DVB) fiber, extraction temperature of 70 degrees C and fiber equilibration time of 15.0 min. The mass spectrum of the dithiaarsenoline of roxarsone showed a base peak that corresponded to the predicted structure at m/z 319 and the tell-tale peak of an arsenic compound derivatized with PDT at m/z 181. Further peaks at m/z 149 and 228 were observed and found to be unique to roxarsone, formed by an interesting internal rearrangement of the ONOH functionality. A linear calibration model was prepared for roxarsone over an environmentally relevant range (0.0-100 microg L(-1)) and a detection limit of 2.69 microg L(-1) (3sigma) was observed. The method was applied to several fortified environmental surface water samples (50 microg L(-1)) where the average recovery for roxarsone was 103+/-10.9%.

Calibration↗

PubMed2003

Demonstration of a method for the direct determination of polycyclic aromatic hydrocarbons in submerged sediments.

We describe the development of a novel method for real-time in situ characterization of polycyclic aromatic hydrocarbons (PAHs) in submerged freshwater sediments. Laser-induced fluorescence (LIF) spectroscopy, a mature technique for PAH characterization in terrestrial sediments, was adapted for shipboard use. A cone penetrometer-type apparatus was designed for probe penetration at a constant rate (1 cm/s) to a depth of 3 m. A field-portable LIF system was used for in situ measurements in which the output of a pulsed excimer laser was transmitted by optical fiber to a sapphire window (6.4-mm o.d.) in the probe wall; fluorescent emission was collected by a separate optical fiber for transmission to the spectrometer on deck. Four wavelengths (340, 390, 440, 490 nm) were selected via optical delay lines, and multiple-wavelength waveforms were created. These multiple-wavelength waveforms contain information on the fluorescence frequency, intensity, and emission decay rate. Field testing was conducted at 10 sites in Milwaukee Harbor (total PAH concentrations ranged from approximately 10 to 650 microg/g); conventional sediment core samples were collected concurrently. The core samples were analyzed by EPA methods 3545 (pressurized fluid extraction, PFE) and 8270C (gas chromatography-mass spectrometry, GC-MS) for PAHs. A partial least-squares regression (PLSR) model wasthen created based on laboratory LIF measurements and PFE-GC-MS of the core samples. The PLSR model was applied to the in situ field test data, and 13 of the 16 EPA-regulated PAHs were quantified with a relative error of <30% overall (the remaining three PAHs were found at levels insufficient to quantify). We additionally describe preliminary source apportionment relationships that were revealed by the PLSR model for the in situ LIF measurements.

Environmental Monitoring↗

PubMed2002

Identification of dimethylchloroarsine near a former herbicide factory by headspace solid-phase microextraction gas chromatography-mass spectrometry.

The application of an improved method based on multidetector gas chromatography to the determination of trace levels of organoarsines in complex matrices is described. The method using headspace-mode solid-phase microextraction (SPME) was applied to a carefully sampled and preserved freshwater sediment core obtained from central Green Bay, Lake Michigan. The sediment core was collected and fractionated in an inert atmosphere. A carboxen/ polydimethylsiloxane-coated SPME fiber (85 microm film thickness) was equilibrated (n = 4) for 60 min at 25 degrees C in the headspace of the sample vessel before introduction to the chromatograph. Conventional quadrupole ion trap mass spectrometry (electron impact ionization), electron capture detection, and pulsed flame photometric detection (arsenic mode) were employed for structure elucidation. A heretofore unidentified species in this region, dimethylchloroarsine (DMCA). was identified. The mass spectrum for DMCA is interpreted based on the observed fragmentation pattern. A bimodal vertical distribution of DMCA in the sediment core sample was observed and its interpretation based on Pb-210 dating is reported.

Arsenicals↗