I. Dzidic

Liquid chromatograph—mass spectrometer—computer analytical systems: A continuous-flow system based on atmospheric pressure ionization mass spectrometry

Abstract Atmospheric pressure ionization (API) mass spectrometry is a novel form of mass spectrometry in which ions are generated in a reaction chamber external to the low-pressure region of a quadrupole mass spectrometer. Using this ionization technique a liquid chromatograph—mass spectrometer analytical system was constructed. The entire effluent stream from the chromatograph is vaporized throught the API source. The primary ionization source for this work was a corona discharge The very high ion densities generated by the corona discharge extend the linear range of the API source into the microgram region.

Atmospheric Pressure Ionization Mass Spectrometry

Abstract Atmospheric pressure ionization (API) mass spectrometry is a novel form of mass spectrometry in which the ionization process is carried out in a reaction chamber external to the mass analyzer region. The mass analyzer serves as a device to detect positive or negative ions present in the reaction chamber, which is maintained at atmospheric pressure.

Atmospheric pressure ionization mass spectrometry : Studies of negative ion formation for detection and quantification purposes

The analytical system described here consists of a gas chromatograph, an atmospheric pressure ionization mass spectrometer designed for operation in the negative ion mode, and a computer. The gas stream from the gas chromatograph is split in order to obtain concurrent but separate detection with a standard electron capture detector and with the mass spectrometer. The ion source of the mass spectrometer is also a duplicate of the standard electron capture detector, so that simultaneous monitoring of the ions and monitoring of the electron capture detection response can also be carried out for the reaction chamber. Negative ions observed under atmospheric pressure ionization conditions are almost always anions of strong gas phase acids. These may be formed by reaction with a gas phase basic ion, or by electron capture reactions. A few organic compounds form stable radical M− ions. Most pesticides, herbicides and fungicides, as well as numerous toxic compounds that are now environmental hazards, form stable anions and show an electron capture response. Most ordinary organic compounds do not form stable negative ions at atmospheric pressure and do not show an electron capture response. The results suggest that an analytical system of this kind will be useful for the detection and quantification of many environmentally hazardous compounds.

Chemical ionization mass spectrometry of nucleosides.

Abstract Basic reactions of nucleosides under conditions of chemical ionization have been investigated, using CH 4 or NH 3 as reagent gases at a pressure of 0.4 mm Hg. C 2 H 4 was found to be useful for the elucidation of some mechanistic and structural details, and was augmented by high resolution techniques. Principal ions corresponded to protonated forms of the molecular ion and the free base. Fewer structural details are generally available from chemical ionization spectra compared with their electron ionization counterparts, although molecular ion ( i.e. M + H) enhancement in the former case offers a major advantage.

The use of stable isotopes in gas chromatography-mass spectrometric studies of drug metabolism.

Abstract Internal reference compounds labeled with stable isotopes have been used to quantify drugs and drug metabolites in urine, plasma and breast milk. [2,4,5-13C3]Diphenylhydantoin, [2,4,5-13C3]phenobarbital and [1-C2H3]valium have been used to quantify diphenylhydantoin, phenobarbital and valium, respectively; [2,4,5-13C3]pentobarbital has been used to quantify amobarbital, secobarbital, butabarbital and pentobarbital. Analyses have been carried out in the picogram to nanogram range by selective ion detection with two gas chromatograph—mass spectrometer—computer systems. Instrumental measurements with picogram samples have also been made using an atmospheric pressure ionization mass spectrometer.

Plasma Desorption Ionization Mass Spectra of Unconjugated Human Steroids

Abstract Steroids, including cortisone, Cortisol, aldosterone, cortol, preg-nanediol, androsterone and 4-androsten-3, 17-dione can be ionized directly, without derivative formation, by plasma desorption ionization to give characteristic mass spectra. The ion products, with isobutane as the reagent gas, indicate the nature of the functional groups and the molecular formula; the spectra are similar to those obtained by chemical ionization methods.