Trimethylsilylated Research Articles

A systematic derivatization technique for characterization of ethoxylates by GC and GCMS

AbstractEthoxylation is one of the common industrial process in which ethylene oxide (EO) is added to compounds containing active hydrogen atom (OH, COOH, SH, NH, etc.) to form surfactants. Alcohol ethoxylates are a major class of non‐ionic surfactants composed of an alkyl chain combined with few EO units. They are widely used in homecare products, personal care products, textiles, oilfield, construction, lubricants, food, paper, leather. The analysis of these ethoxylates possess several challenges since they contain ‘n’ number of EO units (n > 1). With increase in “n,” the product becomes more and more viscous and the boiling point increases making it difficult to analyze by normal gas chromatography (GC) technique. This paper describes a method of derivatizing these ethoxylates so that they can be eluted on a high temperature GC. BSTFA (N, O‐bis (trimethylsilyl) trifluoroacetamide) is used as the derivatizing agent (silylating agent). The ethoxylate combines with BSTFA to form the corresponding trimethylsilylated (TMS) product, which have comparatively lower boiling point. Thus, we detect trimethyl silyl product, which is the resemblance for the ethoxylated product. In this paper, we present a quantitative GC method for the ethoxylates of a few simple alcohols (2‐ethyl hexanol, glycerin), and complex vegetable oils (castor oil). The products formed during the reaction have also been identified on a gas chromatograph coupled with mass spectrometer (GCMS). GCMS shows the mass corresponding to the TMS derivatized product. The derivatization technique not only helps in increasing the volatility of these compounds but also improves the chromatographic efficiency, selectivity, and enhances the detectability.

Automatic Assignment of Molecular Ion Species to Elemental Formulas in Gas Chromatography/Methane Chemical Ionization Accurate Mass Spectrometry.

Gas chromatography-mass spectrometry (GC-MS) usually employs hard electron ionization, leading to extensive fragmentations that are suitable to identify compounds based on library matches. However, such spectra are less useful to structurally characterize unknown compounds that are absent from libraries, due to the lack of readily recognizable molecular ion species. We tested methane chemical ionization on 369 trimethylsilylated (TMS) derivatized metabolites using a quadrupole time-of-flight detector (QTOF). We developed an algorithm to automatically detect molecular ion species and tested SIRIUS software on how accurate the determination of molecular formulas was. The automatic workflow correctly recognized 289 (84%) of all 345 detected derivatized standards. Specifically, strong [M - CH3]+ fragments were observed in 290 of 345 derivatized chemicals, which enabled the automatic recognition of molecular adduct patterns. Using Sirius software, correct elemental formulas were retrieved in 87% of cases within the top three hits. When investigating the cases for which the automatic pattern analysis failed, we found that several metabolites showed a previously unknown [M + TMS]+ adduct formed by rearrangement. Methane chemical ionization with GC-QTOF mass spectrometry is a suitable avenue to identify molecular formulas for abundant unknown peaks.

Comparison of sulfo-conjugated and gluco-conjugated urinary metabolites for detection of methenolone misuse in doping control by LC-HRMS, GC-MS and GC-HRMS.

Methenolone (17β-hydroxy-1-methyl-5α-androst-1-en-3-one) misuse in doping control is commonly detected by monitoring the parent molecule and its metabolite (1-methylene-5α-androstan-3α-ol-17-one) excreted conjugated with glucuronic acid using gas chromatography-mass spectrometry (GC-MS) and liquid chromatography mass spectrometry (LC-MS) for the parent molecule, after hydrolysis with β-glucuronidase. The aim of the present study was the evaluation of the sulfate fraction of methenolone metabolism by LC-high resolution (HR)MS and the estimation of the long-term detectability of its sulfate metabolites analyzed by liquid chromatography tandem mass spectrometry (LC-HRMSMS) compared with the current practice for the detection of methenolone misuse used by the anti-doping laboratories. Methenolone was administered to two healthy male volunteers, and urine samples were collected up to 12 and 26 days, respectively. Ethyl acetate extraction at weak alkaline pH was performed and then the sulfate conjugates were analyzed by LC-HRMS using electrospray ionization in negative mode searching for [M-H](-) ions corresponding to potential sulfate structures (comprising structure alterations such as hydroxylations, oxidations, reductions and combinations of them). Eight sulfate metabolites were finally detected, but four of them were considered important as the most abundant and long term detectable. LC clean up followed by solvolysis and GC/MS analysis of trimethylsilylated (TMS) derivatives reveal that the sulfate analogs of methenolone as well as of 1-methylene-5α-androstan-3α-ol-17-one, 3z-hydroxy-1β-methyl-5α-androstan-17-one and 16β-hydroxy-1-methyl-5α-androst-1-ene-3,17-dione were the major metabolites in the sulfate fraction. The results of the present study also document for the first time the methenolone sulfate as well as the 3z-hydroxy-1β-methyl-5α-androstan-17-one sulfate as metabolites of methenolone in human urine. The time window for the detectability of methenolone sulfate metabolites by LC-HRMS is comparable with that of their hydrolyzed glucuronide analogs analyzed by GC-MS. The results of the study demonstrate the importance of sulfation as a phase II metabolic pathway for methenolone metabolism, proposing four metabolites as significant components of the sulfate fraction.

Driving oxygen coordinated ligand exchange at nanocrystal surfaces using trialkylsilylated chalcogenides

A general, efficient method is demonstrated for exchanging native oxyanionic ligands on inorganic nanocrystals with functional trimethylsilylated (TMS) chalcogenido ligands. In addition, newly synthesized TMS mixed chalcogenides leverage preferential reactivity of TMS-S bonds over TMS-O bonds, enabling efficient transfer of luminescent nanocrystals into aqueous media with retention of their optical properties.

Determination of melamine and cyanuric acid in powdered milk using injection-port derivatization and gas chromatography–tandem mass spectrometry with furan chemical ionization

A reliable, sensitive and eco-friendly injection-port trimethylsilylated (TMS) derivatization and gas chromatography–tandem mass spectrometry (GC–MS/MS) with furan chemical ionization (furan-CI) method was developed to determine melamine and cyanuric acid in powdered milk samples. The effects of several parameters related to the TMS-derivatization process (i.e., injection-port temperature, residence time and volume of silylating agent) and of various CI agents were investigated. Addition of a solution (3 μL) of bis(trimethyl)silyltrifluoroacetamide (BSTFA) containing 1% trimethylchlorosilane (TMCS) reagent to a 20-μL extract from the powdered milk sample gave an excellent yield of the tris-TMS-derivatives of melamine and cyanuric acid at an injection-port temperature of 90 °C. Furthermore, using furan as the CI agent in conjunction with tandem mass spectrometry provided the greatest sensitivity and selectivity of detection. The limits of quantitation (LOQs) for melamine and cyanuric acid were 0.5 and 1.0 ng/g in 0.5-g of powdered milk samples, respectively. The recoveries from spiked samples – after simple ultra-sonication with 5% dimethyl sulfoxide in acetonitrile coupled with n-hexane liquid–liquid extraction – ranged from 72% to 93% with relative standard deviations of lower than or equal to 18%. In three of four real powdered milk samples, melamine was detected at concentrations ranging from 36 to 1460 ng/g; and cyanuric acid was detected in two of these samples at concentrations of 17 and 180 ng/g.

Gas chromatographic quantitative structure–retention relationships of trimethylsilylated anabolic androgenic steroids by multiple linear regression and partial least squares

A quantitative structure–retention relationship (QSRR) study has been performed to correlate relative retention times (RRTs) of trimethylsilylated (TMS) anabolic androgenic steroids (AAS) with their molecular characteristics, encoded by the respective descriptors, for the prediction of RRTs of novel molecules, using gas chromatography time-of-flight mass spectrometry (GC-TOF-MS). The elucidation of similarities and dissimilarities among the data structures was carried out using principal component analysis (PCA). Successful models were established using multiple linear regression (MLR) and partial least squares (PLS) techniques as a function of topological, three-dimensional (3D) and physicochemical descriptors. The models are useful for the estimation of RRTs of designer steroids for which no analytical data is available.

Effect of the Amount of Liquid Phase in Packed Column GC on Air Oxidation Product of Methyl Oleate

The analysis or preparative isolation of a specimen by a packed column gas chromatograph is affected by the kind and amount (concentration) of the liquid phase coated on the stationary phase. In particular, compounds having the same or similar molecular weight and similar functional groups are largely affected. Methyl oleate, which is a typical component of fats and oils, produces hydroperoxide by air oxidation as a first step. After that, various oxygenated compounds with a carbon number of 19 are produced. In this study, the effect of the concentration of ethylene glycol succinate polyester (EGS) as the liquid phase was examined for these compounds. The retention time of the hydroxides increased with an increase in the EGS concentration. The effect of the EGS concentration on the retention time decreased when these compounds were trimethyl silylated (TMS). The retention time of epoxides and oxo compounds increased with an increase in the EGS concentration independently of trimethyl silylation. Correction values were required for all quantitation.

Identification of galactitol and galactonate in red blood cells by gas chromatography/mass spectrometry

Background: Because the products of alternate pathways of galactose metabolism, galactitol and galactonate are important in galactosemia, we sought to identify these compounds in red blood cells (RBC). Methods: RBC extracts were trimethylsilylated (TMS) and analyzed by gas chromatography/mass spectrometry (GC/MS). Results: The presence of both galactitol and galactonate was identified in RBC of 15 galactosemic and 13 normal subjects by their mass spectra and chromatographic comparisons with both unlabeled and 13C labeled standards. The levels in RBC of galactosemics appear to be much higher than those of normal subjects. Conclusion: The determination of these compounds in RBC along with galactose-1-phosphate (gal-1-P) in the same procedure provides the potential for their use in better monitoring of diet therapy in galactosemic patients.

Trace level determination of phenols as pentafluorobenzyl derivatives by gas chromatography-negative-ion chemical ionization mass spectrometry.

A method for the trace level determination of 11 phenols as pentafluorobenzyl (PFB) derivatives by gas chromatography-mass spectrometry (GC-MS) with negative-ion chemical ionization (NICI) is described. First, the conditions for the PFB derivatisation of phenols were optimized and were found to be reaction temperature 80 degrees C and reaction time 5 h. Second, the detection limits using selected ion monitoring (SIM) were compared between trimethylsilylated (TMS) derivatives in the electron ionization (EI) mode and PFB derivatives in the NICI mode. The responses for the PFB derivatives in the NICI mode were 3.3-61 times higher than those of the TMS derivatives in the EI mode. The instrumental detection limits using NICI-SIM ranged from 2.6 to 290 fg. This method was applied to the analysis of phenols in river water using solid-phase extraction. The recoveries of the phenols from a river water sample spiked with standards at 100 ng l-1 with 2-chlorophenol, 4-chloro-3-methylphenol and pentachlorophenol and at 1000 ng l-1 with phenol, 2,4-dimethylphenol, 2,4-dichlorophenol, 2-nitrophenol, 2,4,6-trichlorophenol and 4-nitrophenol were 81.2-106.3% (RSD 5.1-8.0%), except for 2-methyl-4,6-dinitrophenol and 2,4-dinitrophenol, for which the recoveries were 5.8 and 4.2%, respectively, because water contained in the acetone eluate interfered with the derivatisation of these compounds with two electrophilic nitro groups.

Catechin Is Present as Metabolites in Human Plasma after Consumption of Red Wine

Flavonoids are components of fruits, vegetables and wines. An abundance of flavonoids in the diet is correlated with reduced heart disease mortality, suggesting that they act as protective nutrients. However, little is known about the absorption and metabolism of flavonoids after normal foods are consumed. This study measured the levels of one abundant flavonoid, (+)-catechin, and its metabolites in plasma after five male and four female volunteers consumed 120 mL of red wine (RW) one day and de-alcoholized red wine (DRW) on a separate day. Each wine sample contained 35 ± 1 mg catechin (mean ± SEM). Plasma levels of catechin and its metabolite 3′-O-methylcatechin (3′MC) were determined by gas chromatography-mass spectrometry (GC-MS) of the trimethylsilylated (TMS) derivatives. Glucuronide and sulfate conjugates were determined after enzymatic hydrolysis. Before RW or DRW consumption, plasma levels of catechin, 3′MC and all conjugates were <2 nmol/L. After 1 h, average levels of catechin, 3′MC and all conjugates increased to 91 ± 14 nmol/L (RW) and 81 ± 11 nmol/L (DRW). At 1 h, 21 ± 1% of the metabolites were methylated and <2% of catechin and 3′MC were unconjugated. Catechin was present as both a sulfate conjugate and a conjugate containing both glucuronide and sulfate residues. 3′MC was present primarily as a glucuronide conjugate. At every time point, catechin was present almost exclusively as metabolites, and these levels were independent of ethanol. Therefore, if flavonoids are protective nutrients, the active forms are likely to be metabolites, which are far more abundant in plasma than the forms that exist in foods.

Analysis of cyclic boronated and trimethylsilylated phenolalkylamines by gas chromatography and electron impact mass spectrometry

The side chain of phenolalkylamines containing a bifunctional group was derivatized as the cyclic boronate, and then the residual phenolic group was trimethylsilylated. The resulting derivatives were single reaction products in each case, with good gas chromatographic properties and informative mass spectra to afford prominent molecular ions by gas chromatography with electron impact mass spectrometry (GC/EI-MS). The cyclic boronated-trimethylsilylated derivatives yielded the isotope pattern for boron ((10)B:(11)B =-1:4.2) and characteristic ions [M](+), [M - H](+), [M - CH(3)](+), [M - RBO](+), [M - TMSO](+), and [M - TMSO - C(6)H(5)](+) ions in the mass spectra. In order to distinguish between m- and p-phenolalkylamines, the mass spectra of the cyclic phenylboronated-trimethylsilylated (PBA-TMS) derivatives were compared with those of the trimethylsilylated (TMS) derivatives. The TMS derivatives of octopamine (p-) and norfenefrine (m-) showed identical mass spectra, while the PBA-TMS derivatives had mass spectra sufficiently different from one other to distinguish between the isomers. The most prominent ion of the PBA-TMS derivative is the [M - H](+) ion (m/z 310) for octopamine and the [M](+) ion (m/z 311) for norfenefrine. Copyright 1999 John Wiley & Sons, Ltd.

Preparation of TiO 2 films on self-assembled monolayers by sol–gel method

TiO 2 gel films were deposited on three kinds of substrates: (1) a self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS), (2) a trimethylsilylated (TMS) glass surface and (3) a bare SiO 2 glass surface using Ti(OC 3H 7 i) 4-derived titania sols. It was found that OTS SAM induces precipitation of anatase phase at a rather low temperature of 200°C and accelerates anatase-to-rutile phase transformation when a mole ratio of H 2O:Ti(OC 3H 7 i) 4 as low as 0.5 was employed for sol preparation. These effects possibly result from the interaction between the ordered methyl groups of the OTS SAM and the hydrophobic groups of the titania polymers at the gel film/OTS SAM interface.

The Identification of 5′-Deoxy-5′-Methylthioguanosine in Human Urine by Gas Chromatography/Mass Spectrometry

Abstract 5′-Deoxy-5′-methylthioguanosine (MTG) has been identified in human urine by combined gas chromatography/mass spectrometry. Preliminary identification of MTG in the urine of a lung cancer patient was based upon mass spectral comparisons of the trimethylsilylated (TMS) urinary component to both MTA-(TMS)3 and guanosine-(TMS)5. Structural confirmation was obtained by comparing the mass spectral and chromatographic characteristics of authentic MTG to those of the urinary component.

7661. A new experimental method for determining secondary ion yields from surfaces bombarded by complex heterogenous: M G Blain et al, J Vac Sci Technol, A8, 2265–2268

Simultaneous separation and the possibility of quantification of the trimethylsilylated (TMS) bases and nucleosides using gas-liquid chromatography are described. The TMS bases and nucleosides were sufficiently volatile for gas chromatography and readily regenerated the original molecules on very mild hydrolysis. The TMS derivatives were isolated from the trimethylsilylation products of bases and nucleosides, and the structures were established by analyses, NMR spectra, and infrared spectra. The structures of the individual components of gas chromatographic peaks are discussed.

HEAT-TREATMENT OF TRIMETHYLSILYLATED LAYEREDPOLYSILICATES AND THE VARIATION IN THEIRSPECIFIC SURFACE AREAS

Trimethylsilylated (TMS) magadiite and kenyaite were treated thermally and the influence of trimethylsilyl groups on the surface areas of the heat-treated products was investigated. The basal spacings of the TMS-magadiites treated up to 300°C were constant. When TMS-kenyaite was heat-treated, the basal spacing was kept at a constant value until 400°C. The specific surface areas of the products increased up to those temperatures. After the organic groups were burned, the interlayer spaces of the heat-treated TMS-magadiite and TMS-kenyaite were still expanded possibly by the presence of oxidized silyl groups in the interlayer spaces

Identification of Abnormal Urinary Organic Acids in Inherited Metabolic Diseases by Gas Chromatography‐Mass Spectrometry

AbstractA gas chromatography/mass spectrometry (GC/MS) coupled system has been established for the confirmatory identification of abnormal urinary organic acids in inherited metabolic diseases. Samples of patient urines were extracted with an organic solvent and trimethylsilylated (TMS). A mass spectra of gas chromatographically separated TMS derivatives can be obtained using the GC/MS coupled system with a single analytical run. Those compounds with close methylene units (e.g., 4‐hydroxyphenylacetaic acid and phenylpyruvic acid) in the gas chromatograph can be identified by their specific mass spectra. The results indicate that this GC/MS system is a powerful method for identifying abnormal urinary organic acids. These acids can be identified by comparison with authentic mass spectra established in our laboratories or with mass spectra files from other sources or they can be directly identified by analysis of the mass spectrum. By using this system, we were able to make positive identification of several inherited metabolic diseases found in Chinese patients, including phenylketonuria, propionic acidemia, and methylmalonic aciduria. This GC/MS system is a powerful tool for the diagnosis of inherited metabolic diseases.

Isonicotinic acid hydrazide induced changes and inhibition in mycolic acid synthesis in Nocardia and related taxa.

The mycolic acid compositions of Nocardia rubra and related bacteria grown in media containing different concentrations of antituberculous isonicotinic acid hydrazide (INH) were determined in detail by gas chromatography-mass spectrometry. On the basis of molecular species composition, average carbon numbers of mycolic acids were calculated. In Nocardia rubra, N. lutea and Rhodococcus rhodochrous IFO-13161, the ratio of mycolic to non-mycolic fatty acids and the average carbon numbers of mycolic acids were decreased at the INH concentrations of higher than 1 microgram/ml, paralleling with the significant inhibition of growth. In above three species the synthesis of longer chain mycolic acids (longer than C44 or C46 ) was inhibited more significantly than shorter homologues such as C38 or C40 . In contrast, neither growth inhibition nor change in corynomycolic acid composition was observed in Corynebacteria xerosis and Rhodococcus rhodochrous IFO-13165 at the concentration region of INH up to 100 micrograms/ml. The direct mass fragmentographic analysis of the trimethylsilylated (TMS) derivatives of mycolic acid methyl esters, monitoring [M-15] ions of individual molecular species, revealed that the chain shortening of total mycolic acid molecule by INH occurred more greatly in more highly unsaturated subclasses than in less unsaturated subclasses. Furthermore, mass fragmentographic analysis, monitoring fragment ions (A) and (B), due to straight chain and branched chain alkyl units, respectively, demonstrated the inhibition of mycolic acids was not attributed to the shortening of alpha-alkyl chain, but to the inhibition of chain elongation of C28 to C32 straight chain meromycolic acids. It was also indicated the amounts of trehalose mono- and di- mycolate (cord factor) decreased significantly with the addition of INH (1 to 20 micrograms/ml) in the above strains. From the results obtained above, INH appeared to inhibit the synthesis of mycolic acids longer than C44 or C46 specifically by inhibiting chain elongation or desaturation of precursor long chain fatty acids longer than C28 or C30.

Trimethylsilylation of biogenic indoleamines : Practical Kinetic and analytical aspects related to tryptamine and 5-hydroxytryptamine

An attempt is made to answer some practical kinetic and identification questions on the trimethylsilylated (TMS) derivatives of tryptamine (T) and 5-hydroxytryptamine (5HT). Considering the theoretically possible five and 11 TMS derivatives of T and 5HT, respectively, a gas chromatographic—mass spectrometric study of these reaction profiles established the identification of the five T derivatives and all of the six 5HT derivatives whose formation was considered kinetically feasible. Reaction parameters must be optimized to avoid a multiplicity of TMS derivatives in practical applications. A kinetic approach using different catalysts (trimethylsilylimidazole, trimethylchlorosilane, pyridine) indicates that the ease of silylation would follow the order O 5 > 1st N∞ position > N 1 2nd N∞ position. The best results were obtained by reaction with a N,O-bis(trimethylsilyl)trifluoroacetamide—trimethylsilylimidazolepyridine mixture at 70° for 60 min, which enhances the formation of the fully silylated derivatives. The relative merits of the silyl versus the acyl derivatives of these amines are discussed in relation to practical applications.

Gas chromatography and mass spectrometry of some trimethylsilyl derivatives of urinary glucuronides

Guidelines are presented to aid the recognition and interpretation of mass spectra for trimethylsilylated (TMS) glucuronides of aromatic acids and substituted phenols. Masses associated with fragmentation of the derivatized glycon include m e 465, 464, 449, 392, 375, 359, 333, 331, 319, 305, 257, 243, 217, 204, 169, 147, 143, 129, 117, 103, 95, and 93, with m e 375 usually being one of the most abundant masses in the spectrum. Fragmentation of the conjugate after electron impact led to the appearance of a high-abundance fragment of the aglycon having one of the following structures: (a) (TMS) x -Ar-OTMS +, (b) (TMS) x -Ar-OH +, or (e) (TMS) x -AR-O +, where Ar indicates the aromatic ring and (TMS) x indicates polar hydrogens (OH or NH) on the aglycon replaced by TMS groups. Nine of twelve conjugates studied are ethereally linked through a phenolic hydroxyl group; however, the remaining three are ester linked through an aromatic carboxylate group. The latter appcared to be a more labile linkage, since derivatization apparently cleaved the ester bond, forming appreciable quantities of the fully derivatized aglycon and glucopyranurono-(6→1)-lactone. Gas chromatographic retention (methylene units) and mass spectral data are presented for a number of glucuronides isolated from human urine by high-resolution liquid chromatography.

Analyses of glycosaminoglycans by gas-liquid chromatography and the nature of hexuronic acids in heparin

Glycosaminoglycans in microgram quantities were analyzed by gas-liquid chromatography (GLC). Analyses were made of the total and individual hexuronic acids and hexosamines. Glycosaminoglycans were hydrolyzed with formic acid (90%) at 100° for 20 hr in nitrogen atmosphere. The resulting uronic acids and/or lactones were trimethylsilylated (TMS), and the TMS derivatives were analyzed by GLC on an Apiezon column at 190°. Glucuronic and iduronic acids each showed two peaks on the chromatograms. The areas of the peaks were found proportional to the concentration of the sugar. Uronic acids in several polysaccharides were determined by this method using α-methyl- d-glucoside as an internal standard, and the results were found in good agreement with theoretical values. The method, however, was not found suitable for quantitative analysis of total uronic acids in heparin and heparan sulfates due to incomplete hydrolysis of these polysaccharides even after 40 hr. The nature of uronic acids in heparin was investigated by making use of GLC. Peaks corresponding to the retention times of iduronic acid and/or lactones were observed in the chromatograms of heparin after hydrolysis with formic acid. Effluent fractions from GLC column corresponding to peaks on the chromatograms of hydrolyzed heparin were collected and the identity of these fractions with xylose, iduronic acid, and glucuronic acid was established through their infrared spectra. Although there are limitations in determining the total amount of hexuronic acids in heparin and heparan sulfate by the methods described, these techniques are very useful in resolution of ratios of the different hexuronic acids and detection of trace quantities not heretofore possible.