Quantitative analysis of fluorimated ethylchloroformate derivatives of non-protein amino acids using positive and negative chemical ionization gas chromatography-mass spectometry

The GC-MS characterization of the ethylchloroformate derivatives of amino acids in an aqueous medium has been applied to non-protein amino acids. Derivatization of non-protein amino acids using ethylchloroformate, trifluoroethanol, and pyridine produced strong [M + 1]⁺ and [M - 1]⁻ ions in positive and negative chemical ionization (CI) modes, respectively. Twenty-one out of the twenty-three non-protein amino acids studied produced detectable ion chromatograms in both ionization modes when methane was used as the CI reagent gas. Mass spectra of these non-protein amino acid derivatives showed characteristic [M - 19]⁺, [M + 1]⁺, [M + 29]⁺, and [M + 41]⁺ peaks in the positive chemical ionization mode, and [M - 1]⁻, and [M + 35]⁻ peaks in the negative chemical ionization mode. The detection limits and the linear dynamic range of trifluorethanol ethylchloroformate derivatives of non-protein amino acids were studied using positive chemical ionization. The detection limits are mostly in the femtomole range.     

Surface ionization detector with a supersonic free jet for gas chromatography some applications

A new design for a gas chromatographic surface ionization detector based upon hyperthermal positive surface ionization has been developed: There were two requirements: supersonic free jet nozzle and the high work function surface of Re-oxide. This detector, which is highly sensitive in response to all organic compounds, can be operated as an universal detector with an additional selectivity towards some species that have low ionization energy, but with selectivity to a much lesser degree than a conventional surface ionization detector. The minimum detectable amount of toluene is ca. 10⁻¹² g/s with a linearity greater than 10⁴. Some applications are demonstrated using three examples for the analysis of different formulations: (1), terpene mixture, (2), polycyclic aromatic hydrocarbon mixture and (3), alkyl alcohol mixture.     

Plasma chromatography of heroin and cocaine with mass-identified mobility spectra.

Plasma chromatography detects and identifies compounds in trace quantities at atmospheric pressure through characteristic positive and negative mobility spectra. To facilitate use of the technique to detect gas chromatographic effluents, a number of reference mobility spectra for different classes of compounds have been reported. Reference spectra for two more compounds, heroin and cocaine, are presented in this study. The primary ions found in these mobility spectra were determined to be M+, (M - H2)+, and (M - CH3CO2)+ for heroin and M+, (M - C6H5CO2)+ and (M - C6H5CO2 - CO2CH3)+ for cocaine using a directly interfaced plasma chromatograph-mass spectrometer. The identified ions agree closely with those predicted in the ion mobility spectra using mass-mobility correlation data coupled with chemical ionization mass spectrometry data. Also, an independent check demonstrating the reliability of reduced mobility values reported in earlier reference spectra was made.     

Measuring quaternary ammonium cleaning agents with ion selective electrodes

Data for coated-wire, ion selective electrodes (ISEs) are presented for cationic surfactant ions found in common cleaners including benzyldimethyltetradecylammonium, benzyldimethyldodecylammonium, and benzyldimethylhexadecylammonium. The ion exchangers dinonylnaphthalene sulfonic acid, tetraphenyborate, and tetrakis(4-chlorophenyl)borate are examined, showing dinonylnaphthalene sulfonic acid to be the favored species. The ISEs exhibit approximately Nernstian behavior down to the 10⁻⁶ M limit of detection with lifetimes in excess of 50 days when used continuously, and a shelf life of over 100 days. Reaching the upper detection limit at the critical micelle concentration requires use of polymeric-membrane reference electrodes including a new membrane cocktail, which allow response measurements of an order of magnitude higher than the traditional fritted-glass reference electrode. The surfactant ISEs show excellent selectivity over the common metal ions Na⁺, K⁺, Mg²⁺, Ca²⁺, and Cu²⁺ with selectivity coefficients less than 10^−5.3. The ISEs are also selective over the lower molecular weight quaternary ammonium ions tetradecyltrimethylammonium, dodecyltrimethylammonium, benzyldimethyl(2-hydroxyethyl)ammonium, and tetrabutylammonium with selectivity coefficients ranging from 10^−1.7 to 10^−5.5. Use of a single electrode to determine accurately the total cationic surfactant concentration in common cleaning solutions is accomplished with information about concentration dependent interferences and a modified Nikolsky–Eisenman model. Finally, quaternary ammonium surfactants have a deleterious effect on the measurements of pH and common ions like K⁺, Mg²⁺ and Ca²⁺ with polymeric ISEs. This makes it critical to include surfactant electrodes in a detector array when cleaning agents are present.     

Electrospray mass spectrometry of zinc dithiophosphate derivatives and its application to the analysis of engine oil antiwear additives

Electrospray mass spectrometry (ES-MS) has been applied to a variety of zinc O,O′-dialkyldithiophosphate (DTP) derivatives. The neutral Zn(DTP)₂ compounds were converted to the [Zn(DTP)₃]⁻ anions by reaction with excess DTP⁻ and these principal anions are readily observed by ES-MS. Exchange reactions between two different zinc tris(DTP) anions leads to the simultaneous observation of zinc anions containing all possible combinations of ligands even though the species in solution are exchanging rapidly on the NMR timescale. Similar mass spectra are observed upon mixing Zn(DTP)₂ with a different DTP⁻ anion. Reaction of Zn(DTP)₂ with dimethylsulfoxide (DMSO) in methanol solution gives [Zn(DTP)(DMSO)_1,2]⁺ and free DTP⁻ ions which are observed in the positive ion and negative ion ES mass spectra respectively. This latter reaction provides a convenient method for the characterisation and qualitative analysis of engine oil inhibitor and antiwear additives, which contain zinc dithiophosphates with alkyl and aryl substituents.     

Determination and identification of malathion, ethion and dichlorovos using ion mobility spectrometry

Positive ion mobility spectra of different organophosphorus pesticides such as malathion (s-(1,2-dicarb-ethoxyethyl) o,o-dimethyl dithiophosphate), ethion (o,o,o′,o′-tetraethyl s,s′-methylene bis(phosphorodithioate)) and dichlorovos (2,2-dichlorovinyl dimethyl phosphate) have been studied in air at ambient pressure using ion mobility spectrometry method with ⁶³Ni ionization source. The limits of quantification (LOQs) were 1.0 × 10⁻⁹, 1.0 × 10⁻⁹ and 5.0 × 10⁻⁹ g for malathion, ethion and dichlorovos, respectively. The working range of these compounds was about three orders of magnitude and the relative standard deviation (R.S.D.) of repeatability at the 5 μg ml⁻¹ level were all below 15%. Furthermore, in this study, the influences of IMS cell temperature on the ion mobility spectra of these compounds were investigated.     

Detection of lysergic acid diethylamide, delta-9-tetrahydrocannabinol and related compounds by plasma chromatography.

Plasma chromatography as a method for ultratrace qualitative and quantitative detection of organic compounds is especially well suited for detection of gas chromatographic effluents. The optimum range of sample quantity is 10-6 to 10-12 g for detection and identification of a compound by use of its characteristic positive and negative mobility spectra. The type of reference mobility spectra produced by alkanes, aromatics, esters, halogenated compounds, nitrogenated compounds and organic acids have been previously reported. This study presents the reference mobility spectra produced for lysergic acid diethylamide (LSD), delta-9-tetrahydrocannabinol (delta-9-THC), digitoxigenin and several biochemical compounds of research significance. LSD and delat-9-THC in a mixture can be detected and identified by plasma chromatography positive mobility spectra in quantities of 10-7 g or less. All the compounds investigated in this study display strong MH-+ ions along with other ions primarily of the type (M)NO-+, (M)2H-+. None of these compounds exhibits negative mobility spectra.     

Low-molecular-mass anion screening for forensic environmental analyses by capillary zone electrophoresis with indirect UV detection

A method for low-molecular-mass anion screening is described using a buffer composed of 5-sulfosalicylate (SS) as a visualizing ion, hexadimethrine bromide as an electroosmotic flow modifier and Tris as a pH buffer component, at pH 8.6. All ions with effective mobility higher than 2610⁻⁹ m² s⁻¹ V⁻¹ can be separated within 7.5 min under −30 kV. By using the moderately mobile SS (5410⁻⁹ m² s⁻¹ V⁻¹), not only the sensitivity of the detection is improved due to its high UV absorptivity, but also a smaller overall overloading effect is achieved. Meanwhile, the resolution of the high mobility ions, which is normally critical, remains almost the same as compared to a chromate buffer. With an electrokinetic injection, the limit of detection (LOD) of the common ions is 2–13 nM and the detection range is linear up to 0.5–3 μM. With a hydrostatic injection the LOD is 0.15–1 μM and the detection range is linear up to 25–200 μM. The identification of ions is performed by comparing the mobility of the ions with that of standards, taking the apparent and effective mobility of HCO₃⁻, which is normally present in the sample solution, as a reference.     

Pulse radiolysis study of reactions of alkyl and alkylperoxy radicals originating from methyl tert-butyl ether in the gas phase

UV spectra and kinetics for the reactions of alkyl and alkylperoxy radicals from methyl tert-butyl ether (MTBE) were studied in 1 atm of SF₆ by the pulse radiolysis-UV absorption technique. UV spectra for the radical mixtures were quantified from 215 to 340 nm. At 240 nm. σ_R = (2.6 ± 0.4) × 10⁻¹⁸ cm² molecule⁻¹ and σ_RO2 = (4.1 ± 0.6) × 10⁻¹⁸ cm² molecule⁻¹ (base e). The rate constant for the self-reaction of the alkyl radicals is (2.5 ± 1.1) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The rate constants for reaction of the alkyl radicals with molecular oxygen and the alkylperoxy radicals with NO and NO₂ are (9.1 ± 1.5) × 10⁻¹³, (4.3 ± 1.6) × 10⁻¹² and (1.2 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, respectively. The rate constants given above refer to reaction at the tert-butyl side of the molecule.     

Determination of C4-C14 carboxylic acids by capillary zone electrophoresis. Application to the identification of diamide degradation products and partitioning studies.

Capillary zone electrophoresis (CZE) was investigated for the determination of linear saturated carboxylic acid homologues ranging from C₄ to C₁₄. Separation conditions were optimised to overcome the problems of decreasing solubility and decreasing selectivity between successive homologues with increasing chain length. Separations were performed at 20°C, using a 20 kV separation voltage and a pH 8 electrolyte containing 30% methanol. A suitable chromophore (4-aminobenzoate) was added to ensure indirect UV detection of the analytes. Calibration curves and repeatability were established. Minimum detectable concentrations of 3·10⁻⁶ mol l⁻¹ were achieved. Resolution between successive homologues was better than 2. The electrophoretic mobility of each homologue (n=7–14) was assessed and a quasi-linear relationship between the mobility value and 1/n was observed. The quantitative analysis of a diamide degradation solution was performed and compared to potentiometric results. The CZE method was also applied to the determination of C₇–C₁₄ partitioning between an organic medium containing tributylphosphate in n-dodecane and different basic solutions. Their behaviour was established according to the chain length and the pH of the aqueous phase. For C₁₀–C₁₄ compounds, results were validated by comparison with gas chromatographic analysis of the organic phases.     

Simultaneous determination of selenium and lead in whole blood samples by differential pulse polarography

The polarographic reduction of lead in the presence of selenite gives rise to an additional peak corresponding to the reduction of lead (Pb) on adsorbed selenium (Se) on mercury at −0.33 V. The selenium and lead content can be determined using this peak by the addition of a known amount of one of these ions first and then the second ion. The linear domain range of lead is 5.0×10⁻⁷–2.0×10⁻⁵ M and for selenium 5.0×10⁻⁷–1.0×10⁻⁵ M. Using this method 4.90×10⁻⁷ M Se(IV) and 1.47×10⁻⁶ M Pb(II) in a synthetic sample could be determined with a relative error of +2.0% and 1.8%, respectively (n=4). A recovery test after acid digestion for a synthetic sample was 97% for selenium and 96.5% for lead. The method was applied to 1 ml of digested blood, and 328±23 μg l⁻¹ Se(IV) and 850±62 μg l⁻¹ Pb(II) could be determined with a 90% (n=5) confidence interval.     

Collision of molecular anions of benzenedicarboxylic esters with oxygen in a triple quadrupole mass spectrometer

A series of symmetrical phthalate, isophthalate, and terephthalate ester molecular anions were reacted with oxygen in the collision cell of a triple quadrupole mass spectrometer to produce characteristic [M − R]⁻ fragments that can be used to identify these compounds. The [M − R]⁻/M^−· intensity ratios decreased for homologous esters in the following order: phthalates > isophthalates terephthalates. Based on the [M − R]⁻ ion intensities for different alkyl substituents, on ¹⁸O₂ labeling experiments, and on the reactivity of bis(t-butylcyclohexyl)phthalates, it was concluded that M − R anions are generated through an S_N2 nucleophilic displacement at the alpha carbon of the saturated alkyl substituent. For the phenyl ester, the reaction proceeds through attack at the carbonyl carbon.     

Analysis of lipid hydroperoxides and long-chain conjugated keto acids by negative ion electrospray mass spectrometry

Lipid hydroperoxides are important products of enzymatic processes and autooxidation products of polyunsaturated fatty acids. Analysis of such compounds has proved difficult in the past, but negative ion electrospray ionization mass spectrometry was found to be suitable for direct analysis. Abundant [M - H]⁻ ions were observed in full scan mode for hydroperoxyeicosatetraenoic (HPETE), hydroperoxyoctadecenoic acid isomers, and 5,12-diHPETE. Loss of water was observed for all species. Collisional activation and tandem mass spectrometry generated unique and characteristic spectra that shared some common features such as loss of small neutral molecules. More importantly, fragment ions that were indicative of the position of the hydroperoxide were observed. Collision-induced decomposition (CID) of [M - H₂O]⁻ for the HPETE isomers was found to be virtually identical to the CID mass spectra of the [M - H]⁻ anions from corresponding keto-eicosatetraenoic acids, which suggests that the hydroperoxide anions decompose via a dehydration intermediate that resembles the keto acid molecular anion. Cleavage of the double bond allylic to the hydroperoxide formed structurally characteristic ions at m/z 129 from 5-HPETE, m/z 153 from 12-HPETE, and m/z 113 from 15-HPETE. Charge-driven allylic fragmentation led to formation of m/z 203 from 5-HPETE, m/z 179 from 12-HPETE, and m/z 219 from 15-HPETE. Mechanisms consistent with the decomposition of stable isotope analogues are proposed for the formation of these and other characteristic ions. These specific decompositions can be used in multiple reaction monitoring to measure picomolar concentrations of hydroperoxides by direct high performance liquid chromatography tandem mass spectrometry.     

Experimental study and modelling using the ERAS-Model of the excess molar volume of acetonitrile–alkanol mixtures at different temperatures and atmospheric pressure

Densities of {(1−x)CH₃(CH₂)_n−1OH + xCH₃CN} for n=1, 2, 3 or 4 have been determined as a function of composition at 288.15, 293.15, 298.15 and 303.15 K at atmospheric pressure using a vibrating-tube densimeter (Anton Paar DMA 4500, resolution 1×10⁻⁵ g cm⁻³). Excess molar volumes were calculated. The V_m^E values were negative for acetonitrile–methanol mixtures and sigmoid for acetonitrile–alkanols (C₂–C₄) mixtures over the complete mole fraction range. V_m^E values increase in a positive direction with increase in chain length of the alkanols and with the temperature. The Extended Real Associated Solution Model (ERAS-Model) calculations allowing for self-association for the alkanols and complex formation between acetonitrile and alkanols have been used to correlate experimental data. The model is able to reproduce the asymmetrical V_m^E behavior of the studied systems, although agreement between theoretical and experimental values is less satisfactory for some concentration ranges.     

Fingerprint patterns from laser-induced Azido photochemistry of spin-labeled photoaffinity ATP analogs in matrix-assisted laser desorption/ionization mass spectrometry

The photochemical reaction of azide derivatives induced by ultraviolet (UV) laser in matrix-assisted laser desorption/ionization mass spectrometry (MALDI) is reported. A novel synthesized class of azide aromatic derivatives, spin-labeled photoaffinity non-nucleoside adenosine triphosphate (ATP) analogs which are useful probes in study of muscle contraction mechanism, is used in this investigation. In the negative ion MALDI spectra of these ATP analogs, “fingerprint” peaks corresponding to [M − 10 − 1]⁻, [M − 12 − 1]⁻, [M − 16 − 1]⁻, [M − 26 − 1]⁻, [M − 28 − 1]⁻, [M − 41 − 1]⁻, and [M − 42 − 1]⁻ were observed with relative intensities depending on the MALDI matrix. Only the [M − 16 − 1]⁻ is present in the similar mass spectra of the analog in which the azido group is replaced by a hydrogen. A model is suggested for the photochemical reactions of azide derivatives under UV laser irradiation. The photoreaction fingerprint information is diagnostically useful in characterization of azido compounds, especially for spin-labeled photoaffinity non-nucleoside ATP analogs.     

Thin-layer gel chromatography of dyed proteins.

Plasma chromatography as a method for ultratrace qualitative and quantitative detection of organic compounds is especially well suited for detection of gas chromatographic effluents. The optimum range of sample quantity is 10(-6) to 10(-12) g for detection and identification of a compound by use of its characteristic positive and negative mobility spectra. The type of reference mobility spectra produced by alkanes, aromatics, esters, halogenated compounds, nitrogenated compounds and organic acids have been previously reported. This study presents the reference mobility spectra produced for lysergic acid diethylamide (LSD), delta9-tetrahydrocannabinol (delta9-THC), digitoxigenin and several biochemical compounds of research significance. LSD and delta9-THC in a mixture can be detected and identified by plasma chromatography positive mobility spectra in quantities of 10(-7) g or less. All the compounds investigated in this study display strong MH+ ions along with other ions primarily of the type (M)NO+, (M)2H+. None of these compounds exhibits negative mobility spectra.     

Quantitative trace analysis of surfactant mixtures by reversed-phase high-performance liquid chromatography with refractometric detection

Reversed-phase partition liquid chromatography on an octyl column allowed the separation of complex non-ionic poly(ethylene oxide)-type (PEO) surfactant mixtures resulting from the condensation of ethylene oxide with saturated fatty alcohols. As these compounds have no chromophoric group, they were detected by differential refractometry. Accurate quantitation of each oligomer (C_mE_n) allowed the main characteristics of each non-ionic surfactant, i.e., the nature and percentage of the different alkyl chains (with m = number of carbons) and the average number of ethylene oxide units ( ) to be obtained in one analysis. Preparative liquid chromatography was used to isolate pure oligomers with a higher degree of ethoxylation (n =10, 11, 12, 14 and more) than the commercially available standards, in order to determine a wide range of refractometric response factors. It appeared that they are constant as a function of alkyl chain length (C₁₀-C₁₆ range) but that they vary significantly and non-linearly as a function of the degree of ethoxylation, n. It was found that neglecting the variation of response factors can result in a distortion of the average ethoxylation number and in an unsatisfactory quantitative analysis. This chromatographic method, involving a quantitative and reproducible trace enrichment procedure with liquid-solid extraction, allowed the analysis of very dilute PEO mixtures in water. The components of complex PEO mixtures in water were determined at concentrations as low as 0.5 mg 1⁻¹, without any distortion of the distribution, the detection limit being 0.25 μg 1⁻¹ for the less abundant oligomers.     

Determination of fenoterol and salbutamol in pharmaceutical formulations by electrogenerated chemiluminescence

Fenoterol and salbutamol were determined by electrogenerated chemiluminescence (ECL) coupled with flow injection analysis (FIA), using Ru(bpy)₃²⁺ as the luminescent substance. Fenoterol and salbutamol oxidize together with the ruthenium 2,2-bipyridyl at a platinum electrode, which leads to an increase in the luminescent intensity, and this increase is proportional to the analyte concentration. For fenoterol a linear calibration curve within the range from 1.0 × 10⁻⁵ to 1.0 × 10⁻⁴ mol l⁻¹ was obtained with a correlation coefficient of 0.998 (n = 5) and for salbutamol the linear analytical curve was also obtained in this range with a correlation coefficient of 0.995 (n = 5). The relative standard deviation was estimated as ≤2.5% for 3 × 10⁻⁵ mol l⁻¹ for fenoterol solution and as ≤1.3% for 5.0 × 10⁻⁵ mol l⁻¹ salbutamol solution for 15 successive injections. The limit of detection for fenoterol was 2.4 × 10⁻⁷ mol l⁻¹ and for salbutamol was 4.0 × 10⁻⁷ mol l⁻¹. Fenoterol and salbutamol were successfully determined in drug tablets and the soluble components of the matrix did not interfere in the luminescent emission. The results obtained using the luminescent methodology were not statistically different from those obtained by UV-spectrophotometry at 95% confidence level.     

Acidity constants of benzidine in aqueous solutions

The acidity constants of benzidine (Bz) in aqueous solutions determined potentiometrically at 25° were K_a1 = (1.11 ± 0.08) × 10⁻⁵, K_a2 = (1.45 ± 0.12) × 10⁻⁴. The apparent mixed constants in 0.1M sodium nitrate are K_a1 = (5.37 ± 0.28) × 10⁻⁶ and K_a2 = (1.14 ± 0.09) × 10⁻⁴. The ultraviolet spectra were recorded as a function of pH and analysed with these constants to obtain the absorption spectra of H₂Bz²⁺, HBz⁺ and Bz; the corresponding wavelengths of maximal absorption are 247, 273 and 278 nm, and molar absorptivities 1.63 × 10⁴, 1.76 × 10⁴ and 2.26 × 10⁴ 1.mole⁻¹.cm⁻¹.     

Tracing polar benzene- and naphthalenesulfonates in untreated industrial effluents and water treatment works by ion-pair chromatography-fluorescence and electrospray-mass spectrometry

This paper presents a protocol for the determination of a class of polar, ionic and highly water-soluble organic pollutants: benzene- and naphthalenesulfonic acids, compounds widely used in chemical, pharmaceutical, tannery, paper and textile industries. This protocol involves the use of a solid-phase extraction (SPE) followed by ion-pair chromatography-electrospray-mass spectrometry (IPC-ESI-MS). In this work two polymeric solid-phase extraction cartridges (Isolute ENV+ and Lichrolut EN) were compared, with the more effective being Isolute ENV+ sorbent. Recoveries and breakthrough volumes were calculated by loading volumes of 150, 200 and 300 ml of spiked ground water through the SPE columns. To enhance the effectiveness of the methodology, 1 ml of water containing 5 mM TEA was added before eluting with methanol. Average recoveries ranging from 70 to 100% were obtained for a variety of 13 analytes (only two naphthalenesulfonate compounds had recoveries below 50%.). Determination of benzene- and naphthalenesulfonates was accomplished by ion-pair chromatography-fluorescence detection (IPC-FLD).

The ESI-MS parameters were optimized to achieve maximum sensitivity. [M–H]⁻ ion was the base peak using low energies (fragmentor voltage: 80 V). Significant fragmentation of the quasi-molecular [M–H]⁻ ion occurs at higher fragmentor voltages, leading to [M–SO₂H]⁻, [M–SO₃H]⁻ and [SO₃]⁻ as diagnostic ions, but with some sensitivity losses (more than two orders of magnitude when 150 V are applied as fragmentor voltage). Collision-induced dissociation (CID) of the parent ions for the benzene- and naphthalenesulfonates studied gave the [SO₃]⁻ fragment ion common to sulfonated compounds, it has been shown to be characteristic of aromatic sulfonated compounds and could be used as a diagnostic tool to indicate the presence of these compounds.

Limits of detection (signal-to-noise ratio = 3) ranging from 0.03 pg to 0.05 ng, were achieved when 150 ml of ground water were processed and quantified by IPC-FLD. In IPC-ESI-MS, time-scheduled SIM mode with post-column addition of 0.2 m min⁻¹ of methanol was used. LODs range from 0.6 pg to 0.13 ng. In summary, with the development of a methodology based on SPE followed by IPC-ESI-MS, good sensitivity, structural information and unequivocal identification can be achieved.

This protocol was applied to the analysis of surface waters, untreated industrial waste waters and wastewater treatment works effluents and influents. In the case of tannery effluent samples, isomers of naphthalenesulfonic acid were found as major pollutants in concentrations up to 0.8 and 1.0 mg l⁻¹, for 1-naphthalenesulfonate and 2-naphthalenesulfonate, respectively. The main contaminants in wastewater treatment work samples were 2,6-naphthalenedisulfonate, 1-hydroxy-3,6-naphthalenedisulfonate, 3-nitrobenzenesulfonate, 1-naphthalenesulfonate and 2-naphthalenesulfonate, with levels of ug/l.