Pentafluorobenzyl Research Articles

Selected reaction monitoring during gas chromatography/mass spectrometry of eicosanoids.

Gas chromatography/electron capture negative ion mass spectrometry of eicosanoids, as pentafluorobenzyl (PFB) ester, methyl oxime (where applicable), trimethylsilyl (TMS) ether derivatives, is reported using a double-focusing instrument of trisector configuration. Sub-picogram detection limits were observed for prostaglandins E1, E2 and F2 alpha during selected ion monitoring (SIM) of [M-PFB]- ions. Selected reaction monitoring (SRM) of [M-PFB]-----[M-PFB-TMSOH]-, occurring in the first field-free region, was of modest sensitivity, reflecting the stability of the [M-PFB]- ions. The leukotriene B4 (LTB4) derivative was successfully analyzed by SIM at the low-picogram level. In this instance, the fragmentation [M-PFB]-----[M-PFB-TMSOH] occurred in high yield in the first field-free region. The advantageous improvement in selectivity of detection that may be achieved with SRM was evident during the analysis of a serum extract for LTB4.

Pentafluorobenzylation of capsaicinoids for gas chromatography with electron-capture detection

The alkylation of capsaicinoids with pentafluorobenzyl (PFB) bromide for gas chromatography with electron-capture detection was studied. The PFB derivatives were formed within 30 min at 60°C and did not show any signs of decomposition. The alkylated capsaicinoids had a hydrophobic character making them suitable for gas chromatography on a non-polar column. The electron-capture response for the PFB derivatives of capsaicinoids was very sensitive and amounts of capsaicin down to 10 pg were easily detected. The method was succesfully applied to measurement of capsaicinoids in Capsicum products using vanillylamide of octanoic acid as an internal standard.

Studies on steroids : CCXXVIII. Trace analysis of bile acids by gas chromatography-mass spectrometry with negative ion chemical ionization detection

A suitable derivatization method for the trace analysis of bile acids by gas chromatography (GC) in combination with negative ion chemical ionization (NICI) mass spectrometry is described. Of various derivatives for the carboxyl group, the pentafluorobenzyl (PFB) ester provided the highest value of the ratio of the negative top the positive ion current. A chracteristic carboxylate anion [M − 181] − was produced as the most abundant ion by the loss of the PFB group in NICI. The PFB esters were further derivatized to the dimethylethylsilyl (DMES) ethers, whereby lithocholic acid, deoxycholic acid, chenodeoxycholic acid, ursodeoxycholic acid and cholic acid were distinctly separated by GC on a cross-linked methyl silicon fused-silica capillary column. The detection limit for the PFB-DMES derivatives of dihydroxylated bile acids was 2 fg when the fragment ion was monitored at m/z 563 in the NICI mode using isobutane as a reagent gas.

Simultaneous determination of prostanoid plasma concentration by GC-negative ion chemical ionisation MS

For the measurement of prostaglandins several techniques, e.g. bioassay, RIA, HPLC, GC and GC-MS are used. Of these, GC-MS provides the most sensitive and specific methodology. Misinterpretation of data or confusion with other compounds is highly unlikely. Negative ion chemical ionisation mass spectra of methoxime (MO), trimethylsilyl (TMS), pentafluorobenzyl (PFB) derivatives of prostaglandins with CH4 as reagent gas show a fragment ion at m/z (m-PFB)−, which accounts for most of the total ion current. Sensitivity is about a hundred times as high as of electron impact MS. Blood is collected in tubes containing a sodium citrate-indomethacin solution. The plasma is separated and acidified after addition of 2H and 3H standards. Extraction is carried out using a reversed phase Sep-Pak. HPLC separation results in two peaks, the first containing PGE2, TxB2 and 6-k-PGF1α, the second PGF2α. Recovery after HPLC is about 50%. PGE2, TxB2 and 6-k-PGF1α are converted to PFB, MO, TMS derivatives, PGF2α to PFB, TMS derivative. The three MO's are determined in one capillary GC-MS run. Multiple ion detection is carried out by first using the fragment ions m/z 524 and 528 for PGE2, then switching to m/z 614 and 618 for the TxB2 and 6-k-PGF1α fragment ions. Plasma concentrations of 5 healthy volunteers are: PGF2α 3-15, PGE2 2-12, TxB2 7-20 and 6-k-PGF1α 0.5-4 pg/ml. The method is already applied in various experimental and clinical investigations. -Supported by the DFG (Se 263-7).

Confirmation of Pesticide Residue Identity. XI. Organophosphorus Pesticides

Abstract Modification of a method previously published by us generates a wider scope and more rugged procedure for the confirmation of 9 organophosphorus pesticides (OPs). This method involves the hydrolysis of OPs to the corresponding phenols which are then derivatized to their pentafluorobenzyl (PFB) ethers. The ethers are subsequently cleaned up and fractionated on a 5 % deactivated silica gel column and analyzed by electron capture gas chromatography. This procedure enables the confirmation of levels of 10–0.01 ppb OPs from 1 L of water.

Microdetermination of prostaglandins and thromboxane B 2 by capillary gas chromatography and negative ion chemical ionization mass spectrometry

Application of the dimethyl- n-propylsilyl (DMnPS) ether derivatives of prostaglandins (PGs) and thromboxane (TX) B 2 pentafluorobenzyl (PFB) esters to negative ion chemical ionization mass spectrometry (NICIMS) was investigated. These derivatives were separated completely within 10 min by the use of a fused-silica capillary column coated with methyl silicone. In NICIMS, all of the DMnPS ether derivatives of PGs and TXB 2 PFB esters yielded the characteristic negative ion [M  181] − which was produced by elimination of PFB from the molecule. The detection limit of the DMnPS ether derivative of PGF 2α PFB ester was found to be 200 fg with a signal-to-noise ratio of 5 when monitoring the ion of m/z 653 ([M  181] −) in the high-resolution mode (Rb 2500) using ammonia as a reagent gas. The method was applied to the quantitation of PGE 2 and PGF 2α in an extract obtained from the plasma of a lung—heart preparation from a dog.

Zur Analytik von Chlorphenoxyalkansäuren und Chlorphenolen. Teil 2: Nachweis von Chlorphenoxyalkansäuren und Chlorphenolen in der Fischgalle

AbstractThe bile liquid is preserved with ethanol and the protein is precipitated. Prefractionating is done by liquid‐liquid extraction by chloroform and ethyl acetate. The extracts are column‐chromatographically separated on Florisil and subsequently detected by thin‐layer chromatography. For determining the identity of substances, the penta fluorobenzyl derivatives are prepared and chromatographed under the same conditions. Detection is carried out with the aid of ammoniacal silver nitrate reagency and ultraviolet irradiation. The highly polar conjugates of chlorophenoxyalkane acids and chlorophenols which are present in the bile are cracked by acid hydrolysis and then cleaned by re‐extraction. In this way, 2, 4‐D, MCPA, MCPP, 2,4‐dichlorophenol and 2‐methyl‐4‐chlorophenol were detected from Salmo gairdneri. 6… 21 d after the application of the herbicides in the catchment area their concentration in the fish bile amounted to about 200 mg/l, 90% of them having been conjugates. Thus, the biliary excretion of xenobiotic substances offers an important new aspect of biomonitoring by means of fish tests, especially in the range of subacute and chronic toxicity.

Analysis of Pesticide Residues by Chemical Derivatization. VI. Analysis of Ten Acid Herbicides in Sediment1

Abstract A sensitive gas-liquid chromatographic (GLC) method was developed for multiresidue analysis of 10 acid herbicides in sediment. An acidified sediment sample was extracted 3 times with acetonehexane. The combined organic extract was partitioned with acidified water to remove aqueous coextractives. To produce low detection limits for all herbicides including MCPA and MCPB for routine monitoring purposes, pentaf luorobenzyl esters were formed before GLC analysis. Recoveries of all herbicides from fortified sediment samples were better than 80% at the levels studied. Practical detection limits of this method were 10-25 μg/kg (ppb).

Microdetermination of prostaglandins and thromboxane B 2 by gas chromatography using an electron-capture detector

The separation of the dimethylethylsilyl, dimethyl- n-propylsilyl (DMnPS) and dimethylisopropylsilyl ether derivatives of pentafluorobenzyl (PFB) esters of PGF 1α and PGF 2α and methoxime-PFB esters of PGE 1, PGE 2, 6-keto-PGF 1α and TXB 2 was investigated by gas chromatography using an electron-capture detector. Of these silyl ether derivatives, the DMnPS ether derivatives gave the best separation when analysed with the use of a high-performance fused silica capillary column coated with OV-101. The stability of the DMnPS ether derivative of PGF 2α PFB ester was compared with that of the trimethylsilyl (TMS) ether derivative. The recovery of the DMnPS ether derivative of PGF 2α PFB ester in the eluate from a silica gel column was more than 95%, whereas the corresponding TMS ether derivative was partially decomposed and adsorbed on the silica gel column. In addition, the DMnPS ether derivative of PGF 2α PFB ester was stable for at least 1 week during storage in n-hexane solution (10 ng ml −1) at room temperature. The method was applied to the quantitation of PGs in extracts obtained from the urine of spontaneous hypertensive rats. The amounts of PGE 2 and PGF 2α in the urine were calculated to be 92 ± 30 and 29 ± 7 ng ml −1, respectively, when analysed using the orthogonal polynomial equation.

Modification of glass capillary gas chromatographic columns by alkylation of the glass surface with pentafluorobenzyl bromide

Glass surface alkylation with pentafluorobenzyl (PFB) bromide yields glass capillary gas chromatographic columns with modified retention characteristics. Glass-alkylated OV-225 columns have been tested in the analysis of PFB fluoroacetate, and the substantial increase in retention time of this highly volatile compound was found to improve the precision of analysis. PFB-alkylated columns should prove generally useful in gas chromatographic analysis of small relative molecular mass compounds.

Thin-layer chromatography of phenoxyacetic acid herbicides

In our laboratory, the thin-layer chromatography (TLC) of chlorinated catechols’ and cresols’ was examined previously on five different layer materials with several solvent systems in order to develop separation and clean-up methods for these potentially important residues from environmental samples. 4-Chloro-2methylphenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,.%trichlorophenoxyacetic acid (2,4,5-T) are the most important herbicides in Finland3. The crude extracts treated with pentafluorobenzyl bromide are important for the gas chromatographic determination of MCPASS5, MCPA and its metabolitesbi3 and MCPA, 2,4-D and 2,4,5-T”‘-i6 _ m soil. The TLC method has been applied for the separation and identification of MCPA, 4-chloro-o-cresol and 5-chloro-3methylcatechol and their pentafluorobenzyl (PFB) derivatives by using 19 solvent systems on a silica gel layer ” _ In the present study, TLC of compounds I-VI (see Fig. 1) on silica and alumina layers with 11 solvent systems has been extended for the

Analysis of Pesticide Residues by Chemical Derivatization. V. Multiresidue Analysis of Eight Phenoxyalkanoic Acid Herbicides in Natural Waters

A multiresidue method is presented for the gas-liquid chromatographic determination of phenoxyalkanoic acid herbicides in natural waters. Extraction efficiencies of different organic solvents are considered in developing a solvent extraction scheme for these herbicides from water. Reactions for derivatizing these compounds by using pentafluorobenzyl bromide, boron trichloride-2-chloroethanol, and dicyclohexylcarbodiimide-2-chloroethanol were studied in order to obtain extracts with low blanks to provide the lowest detection limits. Advantages and disadvantages of the 3 methods are discussed. Retention times are twice as long for the pentafluorobenzyl (PFB) esters as for the 2-chloroethyl (2-Cl) esters under the same conditions, although electron capture sensitivity to the former was greater. The PFB esters are easier to form, but the 2-Cl reaction is more specific for these herbicides. Solutions from the boron trichloride reaction gave the cleanest blanks.

Analysis of Pesticide Residues by Chemical Derivatization. II. N-Methylcarbamates in Natural Water and Soils

A method for the quantitative determination of several N-methylcarbamates in natural waters and the applicability of the derivative to soil samples using a previously published extraction procedure are described. After extraction of the carbamates from the substrate, the carbamates are hydrolyzed in a 10% methanol-potassium hydroxide solution to form the phenolic hydrolysis products, which are isolated and derivatized with pentafluorobenzyl (PFB) bromide to produce the PFB ether derivatives. The PFB derivatives are cleaned up and fractionated on a silica gel microcolumn and determined by electron capture gas-liquid chromatography (GLC). Eight organophosphate pesticides and 2 phthalate acid esters that hydrolyze to phenols or phthalic acid were evaluated as potential interferences and were found not to interfere with any of the carbamates tested. Quantitative determinations of 0.1 mug carbofuran and 3-ketocarbofuran and 0.5 mug carbaryl, metmercapturon, and Mobam in a 1 L water sample are possible. Propoxur was not determined at levels less than 1 mug/L due to the short GLC retention time of the derivative and interferences from the reagents at the lower levels.

Confirmation of pesticide residue identity: part IX. Organophosphorus pesticides.

This paper describes a confirmation procedure for residue levels of dyfonate, dichlorofenthion and cyanox. After extraction and quantitation by flame photometric detector (FPD)-gas liquid chromatography (GLC), the organophosphorus pesticides are hydrolyzed in a 10% methanolic-potassium hydroxide solution. The phenolic hydrolysis products are then extracted from this solution and reacted with pentafluorobenzyl bromide to produce the pentafluorobenzyl (PFB) ether derivatives. These PFB ethers are subsequently cleaned-up and fractionated on a silica gel micro-column and analyzed by electron capture (EC)- GLC.

Confirmation of Pesticide Residue Identity. VIII. Organophosphorus Pesticides

Abstract A chemical confirmation for 5 organophosphorus pesticides is described. After extraction and quantitation by flame photometric detector gas-liquid chromatography (CLC), the organophosphorus pesticides are hydrolyzed in a 10% methanolic-potassium hydroxide solution, followed by derivatization with pentafluorobenzyl bromide to produce the pentafluorobenzyl (PFB) ethers of the phenolic hydrolysis products. The PFB ethers are subsequently fractionated on a silica gel microcolumn, and analyzed by electron capture GLC. The preliminary chromatographic results of the electron capture GLC analysis of the PFB ethers of the phenolic hydrolysis products of several N-methylcarbamates are also presented. As little as 0.01 ppb ronnel and crufomate and 0.10 ppb parathion, fenitrothion, and methyl parathion in a 1 L water sample can be confirmed.