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

A study of the positive and negative ion, ammonia (NH3 and N2H3) direct chemical ionization mass spectrometry of highly purified prostaglandin endoperoxide (PGH2) is presented. The positive ion spectra were characterized by an intense [M + NH4]+ adduct at m/z 370 and several fragment ions, most notably a [M + NH4-H2O]+ ion at m/z 352 and an ion at m/z 298, assigned as the [M + NH4-72]+ ion of 12-hydroxy-5,8,10-heptadecatrienoic acid formed form PGH2 in the spectrometer. The negative ion spectra of PGH2 were characterized by a base peak at m/z 352 [M]- and by an ion at m/z 334 corresponding to the loss of water from the parent ion. A combination of negative ion and deuterated ammonia reagent gas was used in making assignments and in demonstrating that the spectra observed were due to intact PGH2 and its stable PGE2 and PGD2 isomers formed in the spectrometer. In addition, use of the latter reagent gas was shown to clearly distinguish between several arachidonic acid metabolites, differing in their number of exchangeable protons. Furthermore, preliminary results with several stable prostaglandins indicate that the spectra are sensitive to different functional groups that are present. Consequently, it would appear that negative and positive ion, NH3 (N2H3) direct chemical ionization mass spectrometry would be useful in the analysis of labile arachidonic acid metabolites, without the need for prior derivatization.

A fast, nondestructive purification scheme for prostaglandin H2 using a nonaqueous, bonded-phase high-performance liquid chromatography system.

Arachidonic acid metabolism produces several biologically important compounds including the leukotrienes and prostaglandins. Prostaglandin H2 (PGH2) is the first metabolite in the arachidonic acid cascade leading to all other prostaglandins. Pivotal to our understanding of PGH2's biology is the ability to separate it in pure form from the numerous other arachidonic acid metabolites produced in a biological milieu. The extensive literature on PGH2 biology and metabolism has relied almost exclusively on the traditional method of separation using gravity flow silicic acid columns. In our hands, such PGH2 preparations were found to contain varying amounts of 12-hydroxy-5,8,10-heptadecatrienoic acid (HHT), PGE2, PGF2 alpha and other minor impurities as determined by further chromatographic and mass spectral analyses. Analytical separation of PGH2 and other arachidonic acid metabolites has been accomplished using reversed-phase HPLC. However, the labile nature of this molecule in aqueous systems makes such techniques unacceptable for preparative isolation of high purity PGH2 and has necessitated the development of a totally nonaqueous separation. To this end, we attempted several stationary phases and found that the cyano-bonded phase showed the best selectivity for resolving PGH2 from its major contaminants. Separations were performed on self-packed columns using a hexane-isopropanol gradient. Peaks were detected both by liquid scintillation counting and uv spectrophotometry (214 nm). Structure assignments were made by chromatographic comparison with authentic standards (PGF2 alpha, PGE2), biological activity (PGH2--platelet aggregation), and by ammonia direct chemical ionization mass spectrometry (HHT, hydroxy-5,8,10,14-eicosatetraenoic acid, PGH2, PGE2, PGF2 alpha). The latter technique, which by its very nature volatilizes all organic material in the sample, was particularly useful in determining not only that the PGH2 preparations were free from the aforementioned side products, but that they were also free from lipid, protein, and other potential residues frequently found in biological preparations.

Separation of nucleosides and nucleotides by reversed-phase high-performance liquid chromatography with volatile buffers allowing sample recovery.

Reversed-phase high-performance liquid chromatography using a C18 column with volatile buffers as the eluant was applied to the separation of a number of nucleosides and nucleotides. Groups of seven nucleosides and five nucleoside monophosphates were separated isocratically employing 0.1 M trimethylammonium acetate and 2% acetonitrile at pH 7.0. Groups of seven nucleoside diphosphates and seven nucleoside triphosphates were separated with 0.1 M triethylammonium bicarbonate and 2% acetonitrile titrated to a pH of 7.1 with acetic acid. The techniques described give resolution and separations comparable to nonvolatile buffers. Moreover, the eluant trimethylammonium acetate or triethylammonium bicarbonate buffer can easily be removed in vacuo from the column effluent, making the technique useful for preparative separations of these compounds. The observed elution pattern of nucleoside phosphates suggests that "paired-ion" chromatography is involved in the separation.

Extraction of organic acids by ion-pair formation with tri-n-octylamine. Part 7. Comparison of methods for extraction of synthetic dyes from yogurt.

Synthetic dyes were extracted from yogurt by different methods, but all methods had in common a liberation of dyes from the food followed by ion-pair formation with tri-n-octylamine. Extraction with pH 5.5 phosphate buffer gave high recoveries for 5 of the 7 dyes investigated and was relatively fast. Precipitation of proteins followed by polyamide adsorption and desorption gave high yields for all the dyes but was tedious and long.

Extraction of organic acids by ion-pair formation with tri-n-octylamine. Part 6. Determination of sorbic acid, benzoic acid, and saccharin in yogurt.

The sorbate content of commercial yogurt samples is determined by reverse phase liquid chromatography following ion-pair extraction with tri-n-octylamine. Mean recoveries (70-88%), precision (1.1-3.3% RSD), and detection limit of the method are presented for sorbic acid, benzoic acid, and saccharin.

Extraction of organic acids by ion-pair extraction with tri-n-octylamine - VIII. Identification of synthetic dyes in pharmaceutical preparations.

Synthetic dyes were extracted from syrups, oral suspensions, tablets, gelatin capsules, suppositories and granules by ion-pair formation with tri-n-octylamine (TnOA) and back-extracted with perchlorate ions. Identification was performed by TLC on cellulose layers and by reversed phase ion-pair HPLC.

Extraction of organic acids by ion-pair formation with tri-n-octylamine. Part V. Simultaneous determination of synthetic dyes, benzoic acid, sorbic acid, and saccharin in soft drinks and lemonade syrups.

Synthetic dyes, benzoic acid, sorbic acid, and saccharin are extracted simultaneously from soft drinks with 0.01M tri-n-octylamine at pH = 5.5 and are back-extracted to an aqueous phase with 0.1M sodium perchlorate. The perchlorate solution is injected directly into the reverse phase liquid chromatographic system which permits the separation of all the substances investigated. Forty-six commercial samples of soft drinks and 11 lemonade syrups were analyzed. All samples conformed to the legal prescriptions.

High performance liquid chromatographic and colorimetric determination of synthetic dyes in gelatin-containing sweets, following polyamide adsorption and ion-pair extraction with tri-n-octylamine.

Dyes are determined in gelatin-containing sweets. The gelatin must be eliminated first because it interferes with the normal ion-pair extraction of dyes with tri-n-octylamine to chloroform. Techniques such as precipitation of gelatin with organic solvents, and acid and enzymatic digestion of gelatin are shown to be unsuccessful because the remaining gelatin still influences the extraction scheme. Positive results are obtained when dyes are adsorbed on polyamide, gelatin is washed away, and dyes are desorbed with a methanol-ammonia mixture. Dyes are identified by thin layer chromatography and high performance liquid chromatography (HPLC), and quantitated by HPLC or colorimetry.

Isolation, identification, and determination of food dyes following ion-pair extraction.

Food dyes are extracted as ion-pairs with tri-n-octylamine and tetrabutylammonium. Extraction from aqueous solutions to chloroform is quantitative with 0.1M counter ion concentrations. The dye may be back-extracted to an aqueous phase with chloride, bromide, iodide, nitrate, or perchlorate ions; perchlorate is most successful. The method is applied to the qualitative analysis of dyes in grenadine, pickles, and milk desserts, and quantitative analysis in alcoholic beverages. Commercial samples are analyzed by using a standard addition method.