Electrochemically modulated preconcentration and matrix elimination for organic analytes coupled on-line with electrospray mass spectrometry.

Demonstrated for the first time is the use of electrochemically modulated preconcentration and sample matrix elimination combined on-line with electrospray mass spectrometry (EMPM/ES-MS) for the enhanced analysis of organics by ES-MS. EMPM is similar to adsorptive stripping analysis. Accumulation of the targeted analytes at the working electrode of an on-line electrochemical flow cell is accomplished via a nonelectrolytic adsorption process that is controlled through the proper combination of the solvent system, the working electrode material, and applied potential. Once on the electrode, the analyte may be washed free of sample matrix components detrimental to mass spectrometric detection. The potential applied to the electrode during the detection step is chosen to release or strip the analytes unaltered back into the solvent stream for mass spectrometric detection rather than to oxidize or reduce them as would be the case for electrochemical detection. Thus, retention and elution of a target analyte with EMPM are controlled by switching the working electrode potential, rather than via a switch in mobile-phase composition, as is done in more traditional preconcentration and cleanup schemes used on-line with ES-MS. The proof-of-principle studies described here use the breast cancer drug tamoxifen and a metabolite, 4-hydroxytamoxifen, as the target analytes. A thin-layer, flow-by electrode cell with a glassy carbon working electrode is used as the preconcentration device. The nature of the working electrode, the solvent systems, and the electrode potentials necessary to accumulate and strip tamoxifen and 4-hydroxytamoxifen are discussed. Calibration curves were fitted using the Langmuir isotherm. Detection limits (DLs) using a 5.0 min preconcentration period with selected reaction monitoring for tamoxifen (m/z 372 --> 72) were bracketed as 0.010 nM < DL < 0.025 nM. The ability to simultaneously detect low nanomolar levels of both tamoxifen and 4-hydroxytamoxifen in pristine solution and 1/10 diluted urine is also demonstrated.

Anodic stripping voltammetry coupled on-line with inductively coupled plasma mass spectrometry: optimization of a thin-layer flow cell system for analyte signal enhancement.

Parameters affecting analyte signal enhancement in anodic stripping voltammetry-inductively coupled plasma mass spectrometry (ASV-ICP-MS), using a thin-layer ASV cell and microconcentric nebulization (MCN), have been examined. Silver was used as a test analyte and was deposited at a glassy carbon working electrode. The MCN allowed use of solution flow rates that were beneficial to optimum electrolytic performance of the thin-layer cell. High analyte deposition efficiencies obtained with the thin-layer cell, combined with minimal sample consumption of the MCN, allowed substantial signal enhancement (>400 times higher than continuous nebulization level) to be obtained with 2-3 mL of sample and deposition times of less than 30 min. Signal enhancement was strongly influenced by the opposing effect of flow rate on the electrolytic deposition efficiency (deposition efficiency decreases with increasing flow rate) and on the quantity of analyte delivered to the cell (analyte mass throughput increases with increasing flow rate). Excellent linearity for stripping peak heights was demonstrated for a wide range of analyte deposition times and for peak heights and peak areas (r > 0.999) over a wide concentration range (25 ng/L-20 µg/L). Precision was good (RSD typically <3% for n = 3-6) except for a high Ag blank contributed to by corrosion of the counter electrode and by Ag diffusion from the reference electrode into the cell. Details of the flow manifold and ASV cells are discussed, along with relevant performance characteristics of the MCN.

Freshly fractured quartz inhalation leads to enhanced lung injury and inflammation. Potential role of free radicals.

Silicosis is a devastating pulmonary disease that continues to occur in industrial workplaces. Its pathogenesis is under critical evaluation, and this report provides new concepts on the possible early events that occur in lungs resulting from the inhalation of freshly fractured versus aged quartz in the development of two diverse disease entities. In this study, we evaluated the biochemical and pathologic changes in the lavagate and lungs of rats exposed to freshly fractured quartz (generated by jet milling), aged quartz (milled then aged for 2 mo prior to use), or clean air 5 h a day for 10 d over a 2-wk period. The concentration of crystalline quartz in the chambers averaged 20 mg/m3. Particle concentrations and particle size were similar for the freshly milled and aged quartz exposures. However, free radical concentrations associated with the freshly milled quartz samples were significantly higher than those for aged quartz. After a 2-wk exposure, animals were killed and studied by bronchoalveolar lavage and pulmonary histopathology. Inhalation of aged quartz increased the number of bronchoalveolar lavage cells, demonstrated histopathologic evidence of increased pulmonary infiltrates, showed enhanced concentrations of biochemical markers of lung injury, increased lipid peroxidation, and the ability of pulmonary phagocytes to produce more oxygen radicals. In general, all these pulmonary responses were significantly more pronounced after inhalation of freshly fractured quartz compared with aged quartz. In contrast, antioxidant enzymes showed decreased concentrations in the freshly fractured quartz-exposed group compared with the aged quartz-exposed animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Particle activity and in vivo pulmonary response to freshly milled and aged alpha-quartz.

This study examined the possibility of freshly fractured alpha-quartz being more toxic and inflammatory in vivo than aged quartz of the same composition and particle size. Fresh quartz was generated by a jet mill, and used immediately, while aged dust was stored for two months before use. Both the production of hydrogen peroxide and hydroxyl radicals and the analysis of surface radicals verified the enhanced surface activity of fresh quartz. Male Fischer 344 rats were exposed to fresh or aged alpha-quartz by inhalation (20 mg center dot m-3, 5 h per day, 5 d per week, for 2 weeks) and their pulmonary responses were determined 1--3 d postexposure. Exposure to aged quartz resulted in an increase in cytotoxic and inflammatory parameters. In comparison, the inhalation of freshly cleaved quartz resulted in dramatically greater increases in all of the pulmonary responses. This finding suggests that exposure to freshly machined quartz may result in a greater risk of pulmonary disease.

Determination of arsenic(III) and selenium(IV) using an on-line anodic stripping voltammetry flow cell with detection by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry.

An on-line anodic stripping voltammetry (ASV) flow system, interfaced with inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICPMS) detectors, has been used for determination of arsenic(III) and selenium(IV) and for elimination of polyatomic interferences which arise from chloride in sample matrices. Details of the working electrode preparation are discussed. Arsenic signals in ICP-AES were enhanced by as much as 10 times through preconcentration of sample volumes up to 5 mL. Using ICP-AES detection, recoveries for analyte spikes in 1:10 diluted urine were 102% for As(III) (matrix-matched standards) and 91% for Se(IV) (standards in electrolyte). Using ICPMS detection, determination of certified Se(IV) and Se(IV) spikes in diluted NIST SRM 2670 elevated urine gave recoveries of 92-103%, while recoveries of As(III) spikes in diluted NIST SRM 2670 urine ranged from 94 to 113%. High levels of chloride matrix exhibited little effect on the arsenic signal with ICP-AES or ICPMS detection. Elimination of the polyatomic interference ArCl+ in ICPMS was very efficient for diluted NIST SRM 2670 urine and for a synthetic matrix of 1000 micrograms/mL chloride.