Positive Chemical Ionization Mass Spectrometry Research Articles

Desorption chemical ionization mass spectrometry of C‐glycosylflavones

AbstractSeventeen natural C‐glycosylflavones have been analysed using positive desorption chemical ionization mass spectrometry with ammonia as reagent gas. This technique provides the molecular weight, information for the identification of the aglycone, the sugar sequence, and the characterization of the C‐sugar (hexose, pentose). The distinction between mono‐C‐glycosylflavones, di‐C‐glycosylflavones, C‐glycosylflavone 2″‐O‐glycosides, and di‐C‐glycosylflavone 2‴‐O‐glycosides is also obtained.

Characterization of triacylglycerols in saturated lipid mixtures with application to SALATRIM 23CA

SALATRIM 23CA is a member of the SALATRIM family of triacylglycerols developed by RJR Nabisco Co. It is an interesterification product of triacetin, tripropionin, and hydrogenated canola oil. To characterize this sample, a combination of reversed-phase high-performance liquid chromatography and high-temperature capillary gas chromatography (HTCGC) in sequence was used to separate the SALATRIM 23CA into individual components. An on-line coupling of HTCGC with positive chemical ionization mass spectrometry revealed the structure of the individual components. To obtain detailed quantitative information, a combination of a 5-m OV-1 capillary column and a 25-m methyl 65% phenyl silicone Al-clad column was used to determine the quantities of acylglycerols

Determination of trace amounts of highly hydrophilic compounds in water by direct derivatization and gas chromatography ? mass spectrometry

A new procedure has been developed to derivatize a large set of highly hydrophilic substances ((poly) hydroxy and/or (poly)carboxylic acids, glycols and dihydroxybenzenes) directly in water. The key element of the method is the derivatizing agent used, n-hexyl chloroformate, which proved to be much more effective than other alkyl and aryl chloroformates. Detection limits in the low μg/L range were found for most of the compounds studied, using positive ion chemical ionization mass spectrometry as the detection technique. Calibration curves exhibited a good linearity over 2–3 orders of magnitude, so that quantitative determinations were possible. Among the experimental parameters tested, it was found crucial to introduce the chloroformate slowly and under sonication. The whole derivatization procedure takes only 2–3 min from sample collection to injection into the gas chromatograph.

Identification of carbonyl compounds in environmental samples

Download Hi-Res ImageDownload to MS-PowerPointCite This:Environ. Sci. Technol. 1993, 27, 13, 2745-2753

Liquid chromatography chloride attachment negative chemical ionization mass spectrometry of diacylglycerol dinitrophenylurethanes

Chloride attachment and electron capture negative chemical ionization mass spectra were determined for the 3,5-dinitrophenyl urethanes of natural diacylglycerols following high-performance liquid chromatography on chiral-phase columns using dichloromethane as a source of chloride. For this purpose a chiral column containing the R(+) naphthylethylamine polymer was eluted with an isocratic mixture of either isooctane-f-butyl methyl ether-isopropanol-acetonitrile 80:10:5:5 (solvent A) containing 1% dichloromethane, or with solvent A (20%) and hexane-dichloromethane-ethanol 40:10:1 (solvent B, 80%). The dinitrophenylurethanes gave electron capture molecular and fragment ions in proportions which varied with the composition of the eluting solvent and the ion source pressure. The chloride attachment fragment ions corresponding to the intact diacylglycerols provided a sensitive method of identification and quantitation of the molecular species of the diacylglycerols under all conditions. The detection of the diacylglycerol dinitrophenylurethanes as the negative chloride attachment fragment ions increased the sensitivity and specificity of analysis of the solutes about 100-fold over positive chemical ionization mass spectrometric detection. The detection limit for the dinitrophenylurethanes of natural diacylglycerols was in the low-nanogram range, with the instrument response being linear over two orders of magnitude. For additional structural characterization the dinitrophenylurethanes were subjected to positive chemical ionization mass spectrometry, which resulted in prominent intensities for the [M - DNPU]+ and [RCO + 74]+ ions, but gave no molecular ions. Quantitative analysis of complex mixtures required calibration of the ionization response.

The sensitive determination of abanoquil in blood by high-performance liquid chromatography/atmospheric pressure ionization mass spectrometry.

A method is described for the determination of abanoquil in human blood. The method is based on high-performance liquid chromatography (HPLC)/atmospheric pressure positive ion chemical ionization mass spectrometry, using (2H3)abanoquil as internal standard. Multiple reaction monitoring is employed for selectivity and sensitivity, which enables quantification over the range 10-500 pg ml-1 with acceptable precision and accuracy. This assay methodology illustrates the versatility of atmospheric pressure ionization/tandem mass spectrometry, in conjunction with HPLC, for the separation and quantification of drugs in the subnanogram per millilitre range.

Investigation of some pentasubstituted 1,4‐dihydropyridines by means of fast ion bombardment, chemical ionization and electron impact mass spectrometry

AbstractPositive fast ion bombardment, positive chemical ionization (CI+) and positive electron impact (EI) ionization mass spectrometry were used to investigate a number of relatively large and structurally related organic molecules. Some of the major dissociation pathways observed in the CH4‐CI+ mass spectra are not present under NH3‐CI+ conditions, but are obtained in the collision‐induced dissociation (CID) spectrum of the 50 eV MH+ molecular ion, formed in the latter reaction. The resemblance between the EI mass spectra and their fast ion bombardment counterparts, the effect of changing the energy of the bombarding Cs+ ion beam over the range 2–16 keV and the different degrees of internal excitation of ions formed in different CI reagent gases are discussed.

Mass Spectrometry of Prenylated Flavonoids

The fragmentation patterns originating from the degradation of prenyl group(s) in positive ion electron ionization (EI), fast-atom bombardment (FAB) and chemical ionization (CI) mass spectrometry (MS) of prenylated flavonoids were reviewed. The EI spectra showed the characteristic fragmentation patterns reflecting the location of prenyl group in the flavonoid compounds, whereas the FAB and CI spectra showed relatively monotonous patterns. It was described how the EI and FAB fragmentation patterns are useful for the identification of prenylated flavonoids

Reversed-phase liquid chromatography-mass spectrometry of complex mixtures of natural triacylglycerols with chloride-attachment negative chemical ionization

Short chain triacylglycerols of butteroil and long chain triacylglycerols of menhaden oil were resolved by conventional reversed-phase high-performance liquid chromatography (HPLC) using a linear gradient of 10–90% propionitrile in acetonitrile as the mobile phase. The triacylglycerol species were identified by positive chemical ionization mass spectrometry, which provided [MH-RCOOH] + and [MH] + ions and by negative chemical ionization mass spectrometry with chloride attachment, which yielded exclusively the pseudomolecular ions [M + Cl] −. The negative ions were produced by the inclusion of 1% methylene chloride in the HPLC mobile phase, which did not affect the triacylglycerol elution profile. The restriction of ionization to the chloride-attachment pseudomolecular ions increased about 100-fold the sensitivity of detection of all molecular species and facilitated their quantitation by mass spectrometry. By combining the results of positive and negative chemical ionization mass spectrometry of the eluted peaks it was observed that the complex short chain triacylglycerols showed extensive resolution within isologous saturated carbon number while the polyunsaturated fish oil triacylglycerols showed readily detectable resolution within isologous carbon and double bond number☆. These observations permit the identification and quantitation of molecular species of triacylglycerols in such complex mixtures as butterfat and fish oil, which have thus far proved difficult or impossible.

Identification of natural diacylglycerols as the 3,5‐dinitrophenylurethanes by chiral phase liquid chromatography with mass spectrometry

AbstractThis study reports a facile identification of the molecular species of enantiomeric diacylglycerols by combining chiral phase high‐performance liquid chromatography with positive chemical ionization mass spectrometry. For this purpose the 3,5‐dinitrophenylurethane (DNPU) derivatives ofsn‐1,2(2,3)‐diacylglycerols are separated on an (R+)‐naphthylethylamine polymer column (25 cm × 0.46 cm ID) using an isocratic solvent system made up of hexane/dichloroethane/acetonitrile (85∶10∶5, by vol) or isooctane/tert‐butyl methyl ether/acetonitrile/isopropanol (80∶10∶5∶5, by vol). About 1% of the column effluent (1 mL/min) was admitted to a quadrupole mass spectrometer (Hewlett‐Packard, Palo Alto, CA)via direct liquid inlet interface, and positive chemical ionization spectra were recorded over the range of 200–900 mass units. The DNPU derivatives of diacylglycerols yield characteristic [M‐DNPU]+ and [RCO+74]+ ions for each diacylglycerol species from which the molecular weight and exact pairing of fatty acids can be unequivocally obtained. The characteristic ions appear to be generated in nearly correct mass proportions as indicated by preliminary quantitative comparisons.

The electron impact, chemical ionization and fast atom bombardment positive ion mass spectra of 1,2-bis(sulfonyl)methylhydrazines

A series of bis(sulfonyl)-1-methylhydrazines were analyzed by positive ion electron impact (EI), chemical ionization (CI) and fast atom bombardment (FAB) mass spectrometry. Since these compounds showed activity against the L1210 leukemia, an understanding of their mass spectral behavior is important should the structural characterization of metabolites be required. FAB proved to be the most useful technique, generally providing abundant protonated molecule ion peaks, in contrast to the weak peaks observed with CI (ammonia or isobutane) and the total absence of molecular ion peaks in the EI mass spectra. In addition, utilizing FAB eliminated the problem of thermal decomposition, which was very difficult to control under EI and CI experimental conditions. Fragments observed in FAB and CI mass spectra were consistent with protonation at the methyl-bearing nitrogen. One can locate the R1 and R2 moieties relative to the methyl-bearing nitrogen in FAB and CI by assigning that nitrogen as the site of protonation, with subsequent elimination of R2SO2H.

Identification and determination of propafenone and its principal metabolites in human urine using capillary gas chromatography/mass spectrometry

The capillary gas chromatography/mass spectrometry of trimethylsilyl-trifluoroacetyl, trifluoroacetyl and pentafluoropropionyl (PFP) derivatives of the antiarrhythmic agent propafenone (Rytmonorm), as well as its main metabolites N-despropyl-propafenone and 5-hydroxy-propafenone, have been investigated. Both electron impact and positive isobutane chemical ionization mass spectrometry using the Ion Trap Detector have been evaluated. The presence of propafenone and its co-extracted metabolites in human urine at time intervals after the oral administration of 150 mg Rytmonorm to healthy volunteers was established, and the urinary excretion of propafenone and 5-hydroxy-propafenone was calculated using selective chemical ionization mass spectrometric detection. Only a few per cent of the dose was excreted unchanged in the urine. Large intersubject variabilities had been observed also. The large dynamic range of the Ion Trap Detector and the high correlation coefficients (0.92-0.99) of the calibration curves were striking.

Plasma lipid profiling by liquid chromatography with chloride‐attachment mass spectrometry

A sensitive high-performance liquid chromatographic assay was developed using chloride attachment negative chemical ionization mass spectrometry for detection of glyceryl esters and ceramides, and positive chemical ionization mass spectrometry for detection of free cholesterol and cholesteryl esters in minimal quantities of plasma. The novel technique was validated by high temperature gas-liquid chromatography with flame ionization detection. Sample preparation was achieved by phospholipase C digestion of whole plasma, total lipid extraction and derivatization of any free carboxyl and hydroxyl groups by trimethyl- or tert-butyldimethyl-chlorosilane. The lipids were separated by reverse phase HPLC with 20-90% propionitrile in acetonitrile containing 1% dichloromethane, which served as the reagent and the source of chloride. Negative chemical ionization with chloride attachment is estimated to provide about 100 times higher response for the triacylglycerols and the trimethylsilyl or tert-butyldimethylsilyl ethers of diacylglycerols, and about 500 times higher response for the trimethylsilyl or tert-butyldimethylsilyl ethers of ceramides than positive chemical ionization mass spectrometry. Determination of the full negative chemical ionization mass spectra showed that each glycerolipid and ceramide species yielded a single ionic species corresponding to the chloride-attachment product of the parent ion. The cholesteryl esters and ethers failed to attach chloride and remained undetected by negative chemical ionization. However, the cholesteryl esters and ethers gave a high response for the steroid nucleus in positive chemical ionization mass spectrometry. Chloride attachment negative chemical ionization mass spectrometry is suitable for the unequivocal identification of plasma glycerolipids and ceramides in high-performance liquid chromatography and for the quantitation of molecular species in any unresolved peaks following appropriate calibration of the instrument response.

The mass spectra of 4-aminophenanthrene and its trifluoroacetic anhydride and perflnoropropionic anhydride derivatives

Several aminophenanthrenes have been examined with electron impact mass spectrometry. The trifluoroacetic anhydride (TFAA) and perfluoropropionic anhydride (PFPA) derivatives of 4-aminophenanthrene have been studied with electron impact as well as both positive and negative ion chemical ionization mass spectrometry utilizing methane as a reagent gas. The resulting mass spectra indicate a loss of water from the derivatives and a mechanism is proposed to account for this loss. The spectra also indicate unique fragmentation patterns associated with the position of the substituent, particularly the four position which is in the region of the molecule termed the bay region. Another interesting aspect is the spectral differences observed for the TFAA and PFPA derivatives of 4-aminophenanthrene. The positive ion chemical ionization mass spectrum of the TFAA derivative indicates an ion [M + H - H2O]+; however, the mass spectrum of the PFPA derivative of 4-aminophenanthrene indicates no water loss from the [M + H]+ ion. The negative ion chemical ionization mass spectra of the two derivatives are also very different. The mass spectrum of the TFAA derivative shows an [M - 18]- ion and the PFPA derivative shows successive losses of HF with no apparent loss of water.

Laboratory Investigation of a Poisoning Epidemic in Sierra Leone

In June 1986, an epidemic of poisoning occurred in Sierra Leone, West Africa; it involved 49 persons--with 14 deaths. Our laboratory's approach and investigation of this incident is described. Using positive chemical ionization mass spectrometry and nuclear magnetic resonance spectroscopy, the toxicant was identified as parathion, a highly toxic organophosphorus pesticide. Analysis of various items supported the epidemiologic hypothesis that bread was made from contaminated flour and that the flour became contaminated with parathion during a truck shipment. Modern analytical instruments played a major role in this laboratory investigation and effected the identification of the unknown toxicant within hours of receiving the initial bread sample. Close cooperation and clear communication between the epidemiologic and laboratory teams were important in this investigation.

Stable isotope dilution analysis ofN‐acetylaspartic acid in CSF, blood, urine and amniotic fluid: Accurate postnatal diagnosis and the potential for prenatal diagnosis of canavan disease

A sensitive and selective analytical technique is described for the determination of N-acetylaspartic acid in body fluids using stable isotope dilution in combination with positive chemical ionization mass spectrometry with selected ion monitoring. Control mean and ranges have been established: in urine 19.5 and 6.6-35.4 mumol/mmol creat.; in plasma 0.44 and 0.17-0.81 mumol/L; in cerebrospinal fluid 1.51 and 0.25-2.83 mumol/L; and in amniotic fluid 1.27 and 0.30-2.55 mumol/L. In a patient with Canavan disease, N-acetylaspartic acid concentration was elevated 80-fold in urine and 20-fold in plasma compared to the control means. A subsequent pregnancy of the mother was monitored and the N-acetylaspartic acid concentration in the amniotic fluid was within the control range and a healthy child was born.

Gas Chromatographic and Spectral Properties of Penta-fluorobenzyl Derivatives of 2,4-Dichlorophenoxyacetic Acid and Phenolic Pesticides and Metabolites

Eleven phenols and 2,4-dichlorophenoxyacetic acid, compounds that may be found in body fluids of humans exposed to pesticides, are derivatized with pentafluorobenzyl bromide and characterized by gas chromatography with electron capture detection. These derivatives are further characterized by positive and negative chemical ionization mass spectrometry, nuclear magnetic resonance spectroscopy, and gas chromatography-Fourier transform infrared spectroscopy. Negative chemical ionization mass spectra of all derivatives have an anionic base peak derived from the parent analyte. In the positive mode the nonchlorinated derivatives have base peaks indicative of the analyte, while chlorinated derivatives are cleaved to give the pentafluorobenzyl cation as base peak. The possibility is explored that ortho-substituted phenols might be formed as byproducts in these derivatizations.

The use of electron impact and positive chemical ionization mass spectrometry in the screening of beta blockers and their metabolites in human urine

The use of several mass spectrometry technologies including electron impact (EI) and positive chemical ionization (CI) in both full-scan and multiple ion detection (MID) analysis for the urine analysis of several beta blockers and metabolites has been investigated. These drugs were extracted using an alkaline solid-phase extraction procedure and identified as their respective trimethylsilyl-trifluoroacetyl (TMS-TFA) derivatives on capillary gas chromatography/mass spectrometry. Isobutane proved to be the preferred reagent gas for the positive CI mass spectrometry of TMS-TFA derivatives of beta blockers, in comparison with others, such as methanol, ammonia and methane, since mass spectra with little fragmentation and abundant ions at high mass were obtained. By combining EI mass spectrometry and isobutane positive CI mass spectrometry using the ion trap detector, the identities of the main co-extracted metabolites were confirmed. Absolute detection limits were 0.15 ng for full-scan analysis (EI as well as positive CI mass spectrometry) and 0.08 ng for MID analysis (EI as well as CI mass spectrometry). The detection times of beta blockers in human urine were at least two- to three-fold the elimination half-life of these drugs. The analytical potential of the above mass spectrometric techniques has been discussed.

Quantitative determination of naltiazem in human plasma by gas chromatography/mass spectrometry.

A gas chromatographic/mass spectrometric procedure has been developed for the quantification of a diltiazem analog, naltiazem, in human plasma. The assay utilizes an extraction at neutral pH with hexane:ethylene dichloride:methyl-t-butyl ether (70:20:10), selective ion monitoring, methane or ammonia positive chemical ionization mass spectrometry and stable isotope dilution. The method has been used to analyze plasma concentrations of naltiazem in clinical samples over a range of 2-200 ng ml-1, using 1 ml of plasma.

Confirmation of Phorate, Terbufos, and Their Sulfoxides and Sulfones in Water by Capillary Gas Chromatography /Chemical Ionization Mass Spectrometry

A gas chromatographic/mass spectrometric method capable of confirming phorate, terbufos, their sulfoxides, and sulfones in water is reported. Parents and their metabolites are separated in less than 5 min using a short capillary GC column and high carrier gas linear velocities. Positive ion chemical ionization mass spectrometry generates (M + H) ions indicative of the different molecular weights of the analytes and at least one confirmatory fragment ion for each analyte. Residues have been qualitatively confirmed at the 1 ppb level in fortified water samples from a variety of sources. Apparent residues in control water were less than 0.1 ppb.