Capillary gas chromatography coupled with microplasma mass spectrometry for organotin speciation.

Gas chromatography was coupled with microplasma mass spectrometry for selective detection of organotin compounds. The microplasma ion source was a capacitively coupled radiofrequency helium plasma, which was located inside the high vacuum area of the mass spectrometer. Only 1-3 ml min-1 of helium carrier gas from the gas chromatograph was necessary for sustaining the plasma while 0.15-1.5 ml min-1 of hydrogen was added as reagent gas. Hydrogen was applied for prevention of carbon deposition and served to minimize the interactions between tin and the fused-silica inner surface of the microplasma ion source. Both carbon and tin were detected as positively charged atomic ions, which were expelled from the microplasma ion source and directly focused by electrostatic lenses towards the quadrupole mass analyzer. Tin exhibited high selectivity to carbon (> 10(4)) and a detection limit of 3.5 pg s-1.

Microplasma mass spectrometric detection in capillary gas chromatography.

A simple and miniaturized 350-kHz helium discharge for plasma mass spectrometric detection in gas chromatography (GC) has been developed. The plasma was sustained at low pressure within the end of the capillary GC column (0.32-mm i.d.) inside the ion source housing of a quadrupole mass spectrometer. This allowed direct introduction of ions from the plasma to the mass analyzer using only a repeller and electrostatic lenses to focus the ions. The plasma was sustained in only 25 mL min(-)(1) of helium, which was accepted by the mass spectrometer vacuum system. This low gas flow also served to enhance the energy density of the discharge and to produce a narrow spray of ions toward the mass analyzer. Due to the miniaturized nature of the plasma, it was operated at a low power level (2.0 W), and traces of oxygen were added to avoid deposition of carbon. With this new concept for GC plasma mass spectrometric detection, chlorine was successfully monitored down to the 2.2 pg s(-)(1) level without interference from elements like C, S, P, O, F, and N.

Determination of diflubenzuron in apples by gas chromatography.

A method for the determination of residues of the insecticide diflubenzuron, 1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea, in apples using gas chromatography with electron-capture detection has been developed and validated. The three solvents ethyl acetate, acetone and dichloromethane were tested for extraction of diflubenzuron residues from apples. Dichloromethane gave the highest recovery and the lowest background and was chosen as the extraction solvent. After extraction the residue of diflubenzuron was derivatized with heptafluorobutyric anhydride. The derivative was purified by silica solid-phase extraction using toluene as the eluent. The external standard calibration was linear over the range 0.05-1.0 microgram/ml and the limit of quantification was 0.03 mg/kg apple using 25 g samples. Recovery of diflubenzuron from spiked apples (0.1-0.8 mg/kg) was 80-88% with a relative standard deviation of less than 10% (n = 5). The method was applied to the determination of diflubenzuron residues in apples from a treated field.

Factor C-LHIH which inhibits the luteinizing hormone from basal release and from synthetic LHRH and studies on purification of FSHRH.

PIP: Data on a new entity which inhibits the release of luteinizing hormone (LH), designated as factor C-LHIH, are presented. In vitro assays were carried out with pituitary glands from female rats. Factor C-LHIH and follicle stimulating hormone releasing hormone (FSHRH) initially fractionated together. FSHRH obscured C-LHIH, and FSH assays guided fractionation. Factor C-LHIH and FSHRH were separated and purified by Sephadex and high pressure liquied chromatography. The resulting fractions of C-LHIH inhibited LH-release at 100-500 ng and did not inhibit thyrotropin releasing hormone-thyroid stimulating hormone response.^ieng