Quantitation of a metal deactivator additive by derivatization and gas chromatography--mass spectrometry

The quantitative analysis of phenolic and amine-containing petroleum additives can be challenging. One such compound-N,N'-disalicylidene-1,2-propanediamine, a common metal deactivator additive (MDA)--is thought to inhibit fuel oxidation catalyzed by metals both in the fuel and on surfaces. The ability to measure the concentration of MDA in storage stability tests, thermal-stressing studies, and field samples is important. Quantitating low concentrations of MDA can be difficult because of surface adsorptivity due to the phenol and amine functional groups. This paper describes the shortcomings of direct-injection gas chromatography-mass spectrometry to quantitate MDA as well as a solution to the analytical problem using the common silylation agent BSA to derivatize the MDA. Results demonstrate that the silylation technique is suitable for the determination of MDA concentrations in aviation fuel samples and suggests that the MDA may be readily determined in other petroleum products with a lower detection limit for MDA of 0.5 mg/L. Measurements conducted in heated batch reactors indicate that MDA concentration is reduced as hydrocarbon fuels are stressed. In addition, only free or available MDA is measured by this technique, not MDA that is complexed with metals.     

O-trimethylsilylquinoxalinol derivatives of aromatic alpha-keto acids. Mass spectra and quantitative gas chromatography

As an extension of earlier work on aliphatic alpha-keto acids, a method is described for the quantitative gas chromatographic determination of urinary aromatic alpha-keto acids. The keto acids are derivatized with o-phenylenediamine to yield the quinoxalinols. These compounds are chromatographed after trimethylsilylation. The aromatic keto acids are stabilized by sodium dithionite (4 mg/ml urine) and storage below 0 degrees. The final derivatives are stable for weeks at room temperature. Low resolution mass spectra are reported. The fragmentation mechanisms are elucidated by analysis of O-trimethylsilyl-(TMS)-quinoxalinois, O-(TMS-d9)-quinoxalinois and O-TMS-6(7)-chloroquinoxalinois.     

Comparison of comprehensive two-dimensional gas chromatography and gas chromatography--mass spectrometry for the characterization of complex hydrocarbon mixtures

In this paper, we compare the current separation power of comprehensive two-dimensional gas chromatography (GCxGC) with the potential separation power of GC-mass spectrometry (GC-MS) systems. Using simulated data, we may envisage a GC-MS contour plot, that can be compared with a GCxGC chromatogram. Real examples are used to demonstrate the current potential of the two techniques in the field of hydrocarbon analysis. As a separation technique for complex hydrocarbon mixtures, GCxGC is currently about as powerful as GC-MS is potentially powerful. GC-MS has not reached its potential separation power in this area, because a universal, soft ionization method does not exist. The greatest advantage of GCxGC is, however, its potential for quantitative analysis. Because flame-ionisation detection can be used, quantitative analysis by GCxGC is much more robust, reliable and reproducible.     

Simple and unambiguous method for identifying urinary acylcarnitines using gas chromatography--mass spectrometry

Several inherited metabolic disorders, particularly the organic acidurias and acidemias, are often characterised by excretion of acylcarnitines, especially octanoylcarnitine, in the urine. Clinical investigation of such serious disorders ideally requires a rapid, simple and selective method for determining acylcarnitines in urine. Initial results are given here of a method that may approach this ideal. The procedure involves chemical derivatisation, in which the zwitterionic acylcarnitines are cyclised to volatile lactones, and analysis by gas chromatography and gas chromatography--mass spectrometry. Preparation of urine samples by ion-exchange purification and an illustrative application of the proposed method to a clinical sample are also outlined.     

Microdetermination of caffeine in blood by gas chromatography--mass spectrometry

A micromethod for the quantitative analysis of caffeine present in small quantities (100 microliter) of whole blood is described. It is based on the gas chromatographic--mass spectrometric analysis of chloroform extracts of biological samples. The method is relatively simple, rapid, specific and sensitive; as little as 20 ng of caffeine can be measured.     

Study of disulfide reduction and alkyl chloroformate derivatization of plasma sulfur amino acids using gas chromatography-mass spectrometry

Four disulfide-reducing agents, dithiothreitol (DTT), 2,3-dimercaptopropanesulfonate (DMPS), and the newly tested 2-mercaptoethanesulfonate (MESNA) and Tris(hydroxypropyl)phosphine (THP), were investigated in detail for release of sulfur amino acids in human plasma. After protein precipitation with trichloroacetic acid (TCA), the plasma supernatant was treated with methyl, ethyl, or propyl chloroformate via the well-proven derivatization–extraction technique and the products were subjected to gas chromatographic–mass spectrometric (GC–MS) analysis. All the tested agents proved to be rapid and effective reducing agents for the assay of plasma thiols. When compared with DTT, the novel reducing agents DMPS, MESNA, and THP provided much cleaner extracts and improved analytical performance. Quantification of homocysteine, cysteine, and methionine was performed using their deuterated analogues, whereas other analytes were quantified by means of 4-chlorophenylalanine. Precise and reliable assay of all examined analytes was achieved, irrespective of the chloroformate reagent used. Average relative standard deviations at each analyte level were ≤6%, quantification limits were 0.1–0.2 μmol L⁻¹, recoveries were 94–121%, and linearity was over three orders of magnitude (r ² equal to 0.997–0.998). Validation performed with the THP agent and propyl chloroformate derivatization demonstrated the robustness and reliability of this simple sample-preparation methodology.     

Study of fatty acid profiles in cancer cells grown in culture using gas chromatography--mass spectrometry

The determination of long-chain fatty acids in the phospholipid, triglyceride and free fatty acid fractions of HT29/219 colon cancer cells grown in a medium containing either foetal calf serum or horse serum, was carried out using gas chromatography - mass spectrometry. Several bonded-phase capillary columns were tested for the separation of the fatty acid methyl esters, and a 30-m poly(ethylene glycol) column was found to give optimum separation. The mass spectrometer was set to the multiple ion detection mode to increase the sensitivity of the recording of the characteristic ions, consisting of the molecular ion and the base peak. The phospholipid and triglyceride compositions of the cells were different when the cells were grown in media containing different sera. Differences were also found in the turnover of the acids in the different lipid fractions, the phospholipids being the most important, when the cells were grown in different media. The cellular metabolism and turnover of certain fatty acids differed from others in the same cell. These differences emphasise the importance of a precise knowledge of the lipid composition of the culture medium in in vitro studies of cancer cells.     

Identification of low chlorinated biphenyls in human milk by gas chromatography--mass spectrometry.

Trichlorobiphenyl and tetrachlorobiphenyls in human milk were analysed by gas chromatography--mass spectrometry and mass fragmentography using silicone OV-1 and Apiezon L grease as stationary phases. Low-chlorinated biphenyls had been considered to be excreted rapidly from the body, but in this work quantities of tri- and tetrachlorobiphenyls amounting to approximately 30% of the total of polychlorinated biphenyls (PCBs) accumulated in the milk were identified. This result is important in relation to the quantification of PCBs and in studies of the mechanism of biological degradation.     

Gas chromatography of alpha-keto acids as their O-trimethyl silylquinoxalinol derivatives.

The O-trimethylsilyl (TMS) quinoxalinols are very useful derivatives for the gas chromatography of alpha-keto acids because of their high stability and the absence of stereoisomerism and because of the presence of specific, common and abundant fragments in electron impact mass spectra, which allows the low-level detection of whole groups of keto acids by single-ion detection. In this paper, the chromatographic properties of eleven O-TMS-quinoxalinols on OV-1, OV-17 and Dexsil 300 are reported in terms of methylene units. Also by use of methylene units, the chromatographic isotope effect is analyzed in detail for nine perdeutero-TMS derivatives. The effect is explained by the diminished interaction of the deuterated compounds with the unlabelled liquid phase.     

On-line, inlet-based trimethylsilyl derivatization for gas chromatography of mono- and dicarboxylic acids

An on-line, inlet-based trimethylsilyl (TMS) derivatization technique was optimized and evaluated for quantitative analysis of mono- and dicarboxylic acids. The technique involves co-injection of sample and reagent followed by gas-phase formation of TMS derivatives and analysis by gas chromatography with flame ionization detection. Derivatization efficiencies were determined by comparing measured and theoretical effective carbon numbers and used to optimize the technique with respect to experimental parameters. For analysis of C5-C17 monocarboxylic acids and C2-C10 dicarboxylic acids under optimized conditions, average derivatization efficiencies were > or = 94%, average measurement uncertainties were < or = 5%, and detection limits were approximately 2 ng. The technique was applied to the analysis of carboxylic acids generated from the ozonolysis of cyclic alkenes in a smog chamber.     

Determination of methyl-and ethylmercury compounds using gas chromatography atomic fluorescence spectrometry following aqueous derivatization with sodium tetraphenylborate

Summary An analytical procedure is described for the determination of methylmercury and ethylmercury compounds in fish and sediment samples, using gas chromatography atomic fluorescence spectrometry following aqueous phenylation with sodium tetraphenylborate. The derivatization products were identified by gas chromatography mass spectrometry. The advantages of using phenylation with sodium tetraphenylborate over ethylation with sodium tetraethylborate are discussed. The validation of the analytical procedure was performed by analyzing standard reference material (DORM-2). Applications for the analysis of fish and sediment samples were carried out and compared to other techniques.     

Development of microwave-assisted derivatization followed by gas chromatography/mass spectrometry for fast determination of amino acids in neonatal blood samples

Analysis of amino acids in blood samples is an important tool for the diagnosis of neonatal amino acid metabolism disorders. In the work, a novel, rapid and sensitive method was developed for the determination of amino acids in neonatal blood samples, which was based on microwave-assisted silylation followed by gas chromatography/mass spectrometry (GC/MS). The amino acids were derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) under microwave irradiation. The controlled reaction was carried out employing BSTFA under conventional heating at 120 degrees C for 30 min. Experimental results show that microwave irradiation can accelerate the derivatization reaction of amino acids with BSFTA, and much shorten analysis time. The method validations (linear range, detection limit, precision and recovery) were studied. Finally, the method was tested by determination of amino acids in neonatal blood by the measurement of their trimethylsilyl derivatives by GC/MS in electron impact (EI) mode. Two biomarkers of L-phenylalanine and L-tyrosine in phenylketonuria (PKU)-positive blood and control blood were quantitatively analyzed by the proposed method. The results demonstrated that microwave-assisted silylation followed by GC/MS is a rapid, simple and sensitive method for amino acid analysis and is also a potential tool for fast screening of neonatal aminoacidurias.     

Determination of low-molecular-weight dicarboxylic acids in atmospheric aerosols by injection-port derivatization and gas chromatography-mass spectrometry

A rapid and environmental-friendly injection-port derivatization with gas chromatography-mass spectrometry (GC-MS) method was developed to determine selected low-molecular weight (LMW) dicarboxylic acids (from C2 to C10) in atmospheric aerosol samples. The parameters related to the derivatization process (i.e., type of ion-pair reagent, injection-port temperature and concentration of ion-pair reagent) were optimized. Tetrabutylammonium hydroxide (TBA-OH) 20 mM in methanol gave excellent yield for di-butyl ester dicarboxylate derivatives at injection-port temperature at 300 °C. Solid-phase extraction (SPE) method instead of rotary evaporation was used to concentrate analytes from filter extracts. The recovery from filter extracts ranged from 78 to 95% with relative standard deviation (RSD) less than 12%. Limits of quantitation (LOQs) ranged from 25 to 250 pg/m³. The concentrations of di-carboxylated C2-C5 and total C6-C10 in particles of atmospheric aerosols ranged from 91.9 to 240, 11.3 to 56.7, 9.2 to 49.2, 8.7 to 35.3 and n.d. to 37.8 ng/m³, respectively. Oxalic acid (C2) was the dominant LMW-dicarboxylic acids detected in aerosol samples. The quantitative results were comparable to the results obtained by the off-line derivatization.     

Determination of volatile organic acids in oriental tobacco by needle-based derivatization headspace liquid-phase microextraction coupled to gas chromatography/mass spectrometry

A method coupling needle-based derivatization headspace liquid-phase microextraction with gas chromatography-mass spectrometry (HS-LPME/GC-MS) was developed to determine volatile organic acids in tobacco. The mixture of N,O-bis(trimethylsilyl)trifluoroacetamide and decane was utilized as the solvent for HS-LPME, resulting that extraction and derivatization were simultaneously completed in one step. The solvent served two purposes. First, it pre-concentrated volatile organic acids in the headspace of tobacco sample. Second, the volatile organic acids extracted were derivatized to form silyl derivatives in the drop. The main parameters affecting needle-based derivatization HS-LPME procedure such as extraction and derivatization reagent, microdrop volume, extraction and derivatization time, and preheating temperature and preheating time were optimized. The standard addition approach was essential to obtain accurate measurements by minimizing matrix effects. Good linearity (R(2)> or =0.9804) and good repeatability (RSDs< or =15.3%, n=5) for 16 analytes in spiked standard analytes sample were achieved. The method has the additional advantages that at the same time it is simple, fast, effective, sensitive, selective, and provides an overall profile of volatile organic acids in the oriental tobacco. This paper does offer an alternative approach to determine volatile organic acids in tobacco.     

凝胶渗透色谱-气相色谱-质谱测定花生中乙草胺的残留量

建立了以凝胶渗透色谱(GPC)净化和气相色谱-质谱(GC-MS)技术快速测定花生中乙草胺残留量的方法.经乙腈提取,共提物中的油脂和色素经GPC去除,目标农药采用GC-MS-SIM方式进行定性和定量分析.方法的回收率90%～120%;相对标准偏差2.5%～10%.方法定量限0.005 μg/g.     

凝胶渗透色谱净化-气质联用法测定土壤中三嗪类除草剂

建立了以超声波提取、凝胶渗透色谱净化(GPC)、HP-5 MS石英毛细管柱分离、E1离子源质谱法测定土壤中13种三嗪类除草剂的多残留检测方法.三嗪类除草剂的添加水平为0.010～0.100 mg/kg时,平均回收率为72.1%～118.3%,相对标准偏差为2.6%～19.8%(n=4);方法的检出限为0.30～2.50μg/kg.     

Microwave-accelerated derivatization processes for the determination of phenolic acids by gas chromatography-mass spectrometry

A rapid method for the derivatization of phenolic antioxidants using microwave irradiation has been developed. Six antioxidatively active phenolic components of wines and fruits, namely gallic acid, gentisic acid, vanillic acid, caffeic acid, ferulic acid and p-coumaric acid were used in the model study. The solution of phenolic acids was evaporated to dryness on a rotary evaporator followed by further drying under microwave irradiation (600 W, 30 s). The resultant residue was dissolved in pyridene and treated with bis(trimethylsilyl)acetamide while irradiated by microwave using high power for 30 s. Controlled reaction was carried out employing bis(trimethylsilyl)trifluoroacetamide under conventional heating for 30 min. The trimethylsilyl derivatives were identified and quantified on a gas chromatography/mass selective detector. The mass spectral fragmentation patterns of the derivatives obtained by microwave irradiation were identical to those prepared by heating. The yields of microwave-assisted silylation were comparable to those from conventional heating. The rsd were less than 8% for six replicates. The linearity in wine matrix was nearly perfect. This method is a useful protocol to examine the phenolic constituents in wines and agricultural products.