Qualitative and quantitative analyses of bansyl derivatives of dopamine and some of its metabolites in urine samples by electron impact and field desorption mass spectrometry

Wd, Lehmann; Hd, Beckey; Hr, Schulten

doi:10.1021/ac50005a038

Cited by 31 publications

(2 citation statements)

References 23 publications

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“…Using this technique, the sample (unknown amount) and standard (known amount) are desorbed from the FD emitter in one measurement under identical conditions. Previously, it has been shown that stable isotope dilution is the method of choice for quantitative determinations in FD-MS (12)(13)(14)(15).…”

Section: Resultsmentioning

confidence: 99%

Determination of alkali elements by field desorption mass spectrometry

Lehmann¹,

Schulten²

1977

Anal. Chem.

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The determination of cesium in sample sizes of 0.2 to 1 pL in which 0.3 to 1000 pg of the element was present has been achieved by field desorptlon mass spectrometry and single ion monitoring. The preclslon and accuracy of the method were f10% and about f20%, respectively. A sensitivity between 1.4 and 2.5 X lo-' C per pg was obtained for cesium. The sensitivity for detectlon of the other alkali elements was of the same order of magnitude but decreased slightly from cesium to lithium. Cesium was estimated In spectrograde solvents, in body fluids such as saliva and blood, and in environmental samples such as drinking water, seawater, and a natural aerosol.The extraordinary high sensitivity of field desorption (FD) mass spectrometry (MS) for alkali ions was discovered during the early investigations of organic salts ( I ) . The FD spectra obtained always showed the signals for sodium and potassium ions to be several orders of magnitude more intense than all organic ions when the spectra were recorded on photoplates and the emitter temperature was raised to red heat ( 2 ) . Moreover, the signals for sodium and potassium were also observed with high relative abundance in the F D spectra of organic compounds that contained alkali salts as impurities (3-5). The presence of alkali cations [Cat]' in organic samples leads to an attachment to the organic molecule (M) generating stable [M + Cat]' complexes (cationization) (6-8). This process is useful for molecular weight determination and direct isotope analysis of organic compounds.Although there is unanimous agreement between all groups working in the FD-MS field as to the exceptional sensitivity for alkali cations, no analytical application of this phenomenon has been reported to date. This prompted us to investigate the sensitivity and precision of field desorption mass spectrometry in the single ion monitoring mode for quantitative investigations of alkali ions and to exploit the potential of the technique for trace analysis. EXPERIMENTALThe FD ion currents were recorded on a homebuilt single focusing mass spectrometer of low resolution equipped with a FD source with micromanipulator (6). The FD emitter (at +8 kV) was positioned at a distance of 1 mm from the counter electrode (at -4 kV). Only the first lens (at approximately +2 kV) was used for focusing of the ion beam whereas all other deflection plates were at ground potential. With an entrance slit width of 0.1 mm and an exit slit width of 0.5 mm, a resolution of about 300 (10% valley definition) was achieved. This experimental setup simplifies the operation of the FD mass spectrometer considerably because it allows an easy, fast, and reproducible optimizing of the FD ion currents which is particularly relevant for quantitation.The ions were detected using a channel electron multiplier (Valvo) and a combined counter/ratemeter registration unit (Ortec). The chamel electron multiplier was operated at -3 kV.Field anodes employed were 10-pm tungsten wires activated at high temperature ( I ) . The average length of the...

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Section: Resultsmentioning

confidence: 99%

Determination of alkali elements by field desorption mass spectrometry

Lehmann¹,

Schulten²

1977

Anal. Chem.

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“…Mixtures of dopamine added to urine at the 10-ng//uL level have been determined via the FD method using dopamine-d4 as the internal standard. After formation of the tris-bansyl derivative and TLC cleanup, the relative error was 5% (22).…”

Section: Analytical Applicationsmentioning

confidence: 99%