Search PubMed⌕ Search
Home/Archive/PubMed

PubMed · 9751021

Isotachophoretic separations on a microchip. Normal Raman spectroscopy detection.

P A Walker·M D Morris·M A Burns·B N Johnson
View original source ↗Export metadata ↓

Abstract

Isotachophoretic separations of the herbicides paraquat and diquat are performed in a glass microchip etched channel and monitored on-chip by normal Raman spectroscopy. The 40-micron-wide and 75-micron-deep separation channels are chemically etched in a serpentine design to 21-cm total length. A 120-micron-thick glass cover slip is used to seal the channels. Separation field strengths up to 380 V/cm are used. The microchip is directly coupled to a Raman microprobe. No interfacing is required. Raman spectra are generated with a 2-W, 532-nm NdY-VO4 laser and collected at 8-cm-1 resolution with a holographic transmissive spectrograph and a cryogenically cooled CCD. Data acquisition is at 2-5 spectra/s. Raman isotachopherograms of the pesticides at starting concentrations as low as 2.3 x 10(-7) M (60 ppb paraquat/80 ppb diquat) are presented.

Explore related subjects

DiquatElectrophoresisHerbicidesIndicators and ReagentsMiniaturizationParaquatSpectrum Analysis, RamanJournal ArticleResearch Support, U.S. Gov't, P.H.S.

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

P A Walker, M D Morris, M A Burns, B N Johnson. 1998-09-15. Isotachophoretic separations on a microchip. Normal Raman spectroscopy detection.. https://doi.org/10.1021/ac980195h

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2003

Cluster ions of diquat and paraquat in electrospray ionization mass spectra and their collision-induced dissociation spectra.

Cluster ions such as [Cat+X+nM](+) (n = 0-4); [Cat-H+nM](+) (n = 1-3); and [2(Cat-H)+X+nM](+) (n = 0-2), where Cat, X, and M are the dication, anion, and neutral salt (CatX(2)), respectively, are observed in electrospray ionization (ESI) mass spectrometry of relatively concentrated solutions of diquat and paraquat. Collision-induced dissociation (CID) reactions of the clusters were observed by tandem mass spectrometry (MS/MS), including deprotonation to form [Cat-H](+), one-electron reduction of the dication to form Cat(+.), demethylation of the paraquat cation to form [Cat-CH(3)](+), and loss of neutral salt to produce smaller clusters. The difference in acidity and reduction power between diquat and paraquat, evaluated by thermodynamical estimates, can rationalize the different fractional yields of even-electron ([Cat-H](+) and its clusters) and odd-electron (mostly Cat(+)) ions in ESI mass spectra of these pesticides. The [Cat+n. Solv](2+) doubly charged cluster ions, where n <or= 2 and Solv is the solvent molecule (methanol and/or water), are only observed as very weak peaks in precursor ion CID spectra of the Cat(2+) salt cation at low collision energy. The presence of an anion and a solvent molecule in a cluster is assumed to be related to existence of tight and loose ion pairs, respectively, in multiply charged droplets/ions formed by ESI. The results emphasize again the role of solution chemistry concepts such as acidity/basicity, redox power, and ion-pair formation, for ESI.

Diquat↗
PubMed2001

Spectra interference between diquat and paraquat by second derivative spectrophotometry.

A rapid and accurate method, combining solid-phase extraction and second-order derivative spectrophotomety approaches, is developed for the simultaneous determination of diquat (DQ) and paraquat (PQ) in blood, tissue and urine samples. Supernatant resulting from the precipitation of protein (with trichloroacetic acid) in plasma and tissue or Amberlite IRA-401 resin treated urine are passed through a mini-column packed with Wakogel gel (Silica gel). Analytes are then eluted with a non-organic solvent, 0.2mol/l HCl solution containing 2mol/l NH(4)Cl. UV spectrum of the eluent in 220-350nm range provides effective screen to detect the presence of DQ and/or PQ. In the presence of DQ or PQ alone, the analyte present is quantitated by conventional zero- or second-order derivative spectrophotometry. The calibration curve in the 0.1-5.0mg/l range for either analyte obeys Beer's law. When both DQ and PQ are present, their concentrations are determined by the peak amplitudes of their respective second-derivative spectra after the addition of alkaline dithionite reagent. Interference is negligible when the DQ/PQ concentration ratio is within the 5.0-0.2 range. Using a 2-ml of sample size, the detection limits for DQ and PQ in plasma are 0.02 and 0.005mg/l. The corresponding detection limits for urine samples (10ml sample size) are 0.004 and 0.001mg/l. Recoveries of DQ and PQ in triplicate plasma and urine samples spiked with 0.5mg/l of analytes are 93 and 85%. The precision of the proposed method resulting from triplicate study of spiked urine samples varies from 3.2 to 4.6% at 0.5mg/l of DQ and PQ, respectively.

Diquat↗
PubMed2001

Sample stacking with matrix removal for the determination of paraquat, diquat and difenzoquat in water by capillary electrophoresis.

Conditions for the simultaneous determination of paraquat, diquat and difenzoquat by capillary zone electrophoresis using a stacking technique in a chemically modified capillary have been established. To apply the stacking method with sample matrix removal for the analysis of cations, an anodic electroosmotic flow is mandatory. For quats, 50 mM acetic acid-ammonium acetate (pH 4.0) with 5% (v/v) methanol as electrophoretic buffer and the addition of 0.8 mM cetyltrimethylammonium bromide as wall capillary organic modifier was proposed. Field polarity reversal time was optimised for several sample matrices. Detection was carried out at 220 and 255 nm. Detection limits, based on a signal-to-noise ratio of 3:1, were lower than 15 microg l(-1) for standards in Milli-Q water and two to ten times higher for drinking water samples. Run-to-run and day-to-day reproducibility have been established. The method was successfully applied to the determination of the three herbicides in spiked drinking water.

Diquat↗