Sequential injection analysis coupled to on-line benchtop proton NMR: Method development and application to the determination of synthetic cathinones in seized drug samples.

Synthetic cathinones are a class of new psychoactive substances (NPS), an emerging group of analogues to traditional illicit drugs which are functionalized to circumvent legal regulations. The analytical investigation of NPS by traditional methods, such as gas chromatography-mass spectrometry (GC-MS), is challenging because newly emerging NPS may not yet appear in spectral libraries and because of the inability to determine certain positional isomers. Low-field or "benchtop" proton nuclear magnetic resonance spectroscopy (NMR) is an alternative that provides significant qualitative information but is particularly susceptible to matrix interferences. To this end, the development of a Sequential Injection Analysis (SIA) method which uses solid-phase extraction (SPE) to remove interfering matrix components prior to NMR determination is described. Factors including the type of SPE sorbent, column dimensions, and sample loading and elution conditions were examined. Several cathinone simulants (primary, secondary, and tertiary amines), "DEA exempt" cathinone standards, as well as authentic case samples were studied. The selectivity of the SIA-NMR-UV method was investigated against a broad range of "cutting agents" and was found to successfully remove all compounds tested with the exception of other basic drugs (e.g., acetaminophen). The limit of detection and reproducibility of the method were optimized using a Plackett-Burman screening design and Sequential Simplex optimization. Using a UV detector for dual (in series) quantification, the multivariate-optimized method produced a method limit of detection (3σ) for the cathinone simulant Phenylpropanolamine (PPA) of 23 µmol L-1, and a calibration model, in terms of UV peak area, of Area = 0.19 [PPA, mmol L-1] - 0.04. The optimized method generated ~2 mL of waste per day, and had a footprint of ~1 m2 Finally, the multivariate-optimized SIA-NMR-UV method was successfully applied to several more case samples and the cathinones were definitively identified.

Challenges in the application of conventional PCB quantitation methods to studies of "invasive" freshwater organisms.

We describe significant and unexpected errors in application of a conventional method for the quantitative determination of polychlorinated biphenyls (PCBs) in unusual biological tissue samples. A standard method based upon microwave-assisted extraction (MAE) and gas chromatography tandem mass spectrometry (GC-MS/MS) was applied to a variety of "invasive" freshwater organisms, representing a variety of genera. The 12 "co-planar" PCBs (co-PCBs) were determined at ng g(-1) levels in small samples (ca. 750-1000 mg) of eight freshwater species (n = 172). We found that the conventional method could lead to random and relatively large changes in retention times. A nearly five-fold increase in retention variability was observed for "lower" organisms compared to that observed in the analysis of predatory fish tissue. These unexpected retention time changes would result in misidentifications, and become problematic not only for non-selective detectors such as electron capture but also for MS-based approaches. That is, for electron impact (EI) ionization methods, molecular ions (M(+)) are produced by loss of Cl not only for congeners in the same homolog class but also for fragments of higher homologs (e.g. M - 35 and M - 37), thereby yielding false positive measurement of the target congener when the retention time windows overlap.

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%.

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.

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.

Evaluation of an In Situ, On-Line Purging System for the Cone Penetrometer.

Materials that will be used to construct an in situ, on-line purging system for the cone penetrometer were evaluated. Transfer efficiencies for volatile organic compounds (VOCs) through stainless steel, nickel, aluminum, and Teflon® tubings were determined using a gas-phase mixture of VOCs containing trichloromethane, tetrachloromethane, 1,1,1- trichloroethane, tetrachloroethene, hexane, benzene, toluene, and 1,2-dimethylbenzene. The water content of the gas stream had an insignificant effect on the quantitative transfer of VOCs through Teflon® tubing but was critical to efficiently transfer the compounds through metal tubing, particularly nickel. Transfer efficiencies for all eight analytes in moist gas streams through stainless steel were greater than 95%. Toluene, tetrachloroethene, and 1,2-dimethylbenzene were transferred with 93%, 81%, and 80% efficiency, respectively, when they were drawn through Teflon® PFA (perfluoroalkoxy) tubing. In general, the retention of the VOCs by Teflon® increases with decreasing aqueous solubility of the analyte. The efficiencies at which VOCs were purged from aqueous standards in Teflon® PFA, Type 304 stainless steel, and glass vessels were similar. Stainless steel was superior to nickel, aluminum, and the Teflon® polymers as a material for an in situ, on-line purging system for the cone penetrometer.