Ammonia (NH3 and N2H3) direct chemical ionization mass spectrometry of underivatized prostaglandin-H2 and other selected stable prostaglandins

An improved direct chemical ionization (DCI) mass spectrometric technique, using a polyimide-coated fused silica fiber as an extended probe tip, was used to obtain molecular ions and diagnostic fragment ions of underivatized arachidonic acid, 5-hydroperoxyeicosatetraenoic acid, 15-hydroperoxyeicosatetraenoic acid, leukotriene B4 (LTB4) and, for the first time, of leukotriene A4 (LTA4)-free acid. In this technique, sample compounds are coated onto the fused silica fiber and vaporized in the plume of the reagent gas plasma of a chemical ionization source without external heating of the probe. Both ammonia and isobutane DCI spectra were obtained for each compound. A volatile alkaline eluent system was developed that allowed reversed-phase high-performance liquid chromatography of LTA4 to be followed rapidly by DCI mass spectrometry. With these techniques, the conversion of LTA4 to LTB4 during incubation with human liver microsomes was confirmed. Selected ion monitoring (SIM) of preselected ion fragments in the spectrum increases the selectivity of this technique and improves quantification in the range 100 ng to 10 pg.

Leukotriene biosynthesis: Direct chemical ionization mass spectrometry of underivatized arachidonic acid metabolites

Gut¹,

Trudell²,

Jamieson³

1988

Confirmation of drugs of abuse in urine drug screens by direct exposure probe mass spectrometry

Papa¹,

Ng²,

Robbins³

et al. 1988

A direct exposure probe (DEP) mass spectrometric method was developed to confirm the presence of cocaine (C), phencyclidine (P), benzoyl ecognine (BE) and 11-norcarboxy tetrahydrocannabinol (11-nor-c-THC) in previously screened urine specimens. Essentially, a urine sample is lyophilized overnight and reconstituted in 30 microliters of a 3:1 mixture of ethyl acetate:methanol. One microliter is placed on a rhenium filament and left to air dry. The specimen was analyzed by negative ion chemical ionization DEP using ammonia as reagent gas at 0.20 Torr with an ion source temperature of 100 degrees C. An electronics setting of 1700 V (EM), 0.30 mA filament current, and 100 eV with scanning at m/z 100-650 (1 sec/SCAN) resulted in simple spectra with easily identifiable molecular ions for C, BE, P and 11-nor-c-THC. The sensitivity of the assay was 1 ng for the drugs of abuse. The method was validated by analyzing 50 urine samples that have been previously screened and confirmed for drugs at the University of Illinois Toxicology Laboratory. The results showed that the DEP method confirmed 87%, 71%, 100%, and 85% of the BE, C, P and 11-nor-c-THC. In summary, a rapid and sensitive DEP method for the confirmation of drugs of abuse in urine has been developed which can serve as a useful adjunct to gas chromatographic/mass spectrometric confirmation.

Chemical ionization mass spectral characteristics of analogs of steviol, the aglycone of the plant-derived sweetening agent, stevioside

Hussain

Schilling

Kinghorn

1990

The use the naturally occurring ent-kaurene diterpene glycoside, stevioside, as a sucrose substitute in several countries has resulted in the need for improved methods to analyze its potential metabolites. Altogethe'; 21 diterpenes related in structure to steviol, the aglycone of stevioside, have been subjected to desorption chemical ionization mass spectrometry using methane, ammonia and dimethyl ether as reagent gases. Both methane and ammonia provided the molecular weights of these derivatives, but failed to produce any adduct ions of particular diagnostic value for differentiating compounds in the steviol series.