Pentafluorobenzylation, extractive

Fine DD, Breidenbach GP, Price TL, Hutchins SR (2003) Quantitation of estrogens in ground water and swine lagoon samples using solid-phase extraction, pentafluorobenzyl/... 

In the last few years a number of reports have appeared on an extractive pentafluorobenzylation procedure for phenols and carboxylic acids to enhance their electron-capturing properties. 

Extractive pentafluorobenzylation was described by Jacobsson et al. They extracted 9 mmol of acid with 50 ml of acetone containing 2.8 mmol of pentafluorobenzyl chloride, and added 6 mmol of K2CO3. The reaction was done under reflux for 6 hours, and the mixture was evaporated to dryness in a rotary evaporator. The esters were dissolved in 10 ml of hexane, the solution was washed with 10 ml of water, and further clean-up, if required, was done on a silica gel column (100). 

The first bioanalytical application of LC-GC was presented by Grob et al. (119). These authors proposed this coupled system for the determination of diethylstilbe-strol in urine as a replacement for GC-MS. After hydrolysis, clean-up by solid-phase extraction and derivatization by pentafluorobenzyl bromide, the extract was separated with normal-phase LC by using cyclohexane/1 % tetrahydrofuran (THE) at a flow-rate of 260 p.l/min as the mobile phase. The result of LC-UV analysis of a urine sample and GC with electron-capture detection (ECD) of the LC fraction are shown in Ligures 11.8(a) and (b), respectively. The practical detection limits varied between about 0.1 and 0.3 ppb, depending on the urine being analysed. By use of... 

Saltar and Paasivirta [155] have described a method for the analysis in soils of MCPA (4-chloro-2-methyl phenoxy acetic acid) and two of its main metabolites, 4-chloro-o-cresol and 6-chloromethyl catechol by gas chromatography of their pentafluorobenzyl derivatives (Fig. 9.12). After derivitization of the residue extract, a clean-up procedure was applied. The best recoveries of compounds from soil were obtained when the extraction was performed by shaking with ether-acetone-heptane-hexane (2 1 1 1) from acidified soil and when the clean-up was done by thin layer chromatography (Table 9.17). Detection limits were in the range 20-25ng absolute. 

Thiocyanate Human urine, saliva Derivatization of basic pH sample with pentafluorobenzyl bromide in the presence of Kryptofix 222 B polymer and extraction into methylene chloride then back extraction into isooctane GC with ECD 0.0115 nmol (in 0.2 mL) 83-106 Chen et al. 1994... 

Potable water and raw source water Sample acetylated in situ by addition of acetic anhydride, solvent extracted and concentrated alternatively, extracted acidic sample derivatized by pentafluorobenzyl bromide and cleaned up by column chromatography HRGC-ECD (for pentafluorobenzyl derivative) HRGC-MS (for acetyl derivative) <50 ng/L (pentafluorobenzyl) <50 ng/L (acetyl derivative) 10-64% (pentafluorobenzyl derivative) 70-132% (acetyl derivative) Sitholeetal. 1986... 

A new, fast, sensitive, and solventless extraction technique was developed in order to analyze beer carbonyl compounds. The method was based on solid-phase microextraction with on-fiber derivatization. A derivatization agent, 0-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBOA), was absorbed onto a divinyl benzene/poly(dimethylsiloxane) 65- xm fiber and exposed to the headspace of a vial with a beer sample. Carbonyl compounds selectively reacted with PFBOA, and the oximes formed were desorbed into a gas chromatograph injection port and quantified by mass spectrometry. This method provided very high reproducibility and linearity When it was used for the analysis of aged beers, nine aldehydes were detected 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, pentanal, hexanal, furfural, methional, phenylacetaldehyde, and (E)-2-nonenal. (107 words)... 

A GLC method for the determination of benzoic acid to concentrations as little as 10 ng/mL in plasma and urine was described by Sioufi and Pommier [42]. After addition of an internal standard (3-phenylpropionic acid), benzoic acid was extracted at acidic pH into diethyl ether, whereupon both compounds were derivatized with pentafluorobenzyl... 

Chloro-2-methyl- phenoxyacetic acid Dichloromethane extraction Extracts esterified with 2,3,4,5,6-pentafluorobenzyl bromide, petroleum ether extract analysed by gas chromatography, limit of detection 0.5 - 2 pg/kg [403]... 

Fogelgvist, E., Josefsson, B., and Roos, C., Determination of carboxylic acids and phenols in water by extractive alkylation using pentafluorobenzylation, glass capillary g.c. and electron capture detection, HRC CC, J. High Resolut. Chromatogr. Chromatogr. Commun., 3, 568, 1980. 

Lee et al. [187] developed a multi-residue method with a low detection limit for 10 commonly used acid herbicides in non saline waters. The herbicides were Dicamba, MCPA, 2,4-DP, 2,3,6-TBA, 2,4-D, Silvex, 2,4,5-T, MCPB, 2,4,5-DB and Picloram. The method used solvent extraction and the formation of pentafluorobenzyl esters. The derivatives were quantified by capillary column gas chromatography with electron capture detection. The detection limit was 0.05pg L. Recoveries of herbicides from spiked Ontario lake water (0.5-1.Opg L 1) were 73-108% except for Picloram recovery which was 59% at 0.1 pg L 1. 

Phenoxy carboxylic acids Solid phase -extraction with C18 resin Phenoxyacetic acids derivativised with pentafluorobenzyl bromide, then GLC ppt [409]... 

Extractive alkylation has a reaction scheme identical with that for the previous procedure. The substrate with a carboxyl group reacts in an aqueous solution with a quaternary base and is extracted in the form of an ion pair into a polar solvent of low solvation capacity (dichloromethane) that contains alkyl halide. Low solvation of the anion of the acid and high solvation of the reaction product lead to increased reactivity of the anion and to a rapid reaction with the alkylation agent in the organic phase. Methyl iodide [27] is used to prepare methyl esters and pentafluorobenzyl bromide [28] is used for the preparation of esters providing a high ECD response. 

Anticholinergics, such as atropine and oxyphenonium bromide, which are esters of carboxylic acids, were analysed in plasma and urine as pentafluorobenzyl esters [541,542], The method involves ion-pair extraction of the material under analysis, hydrolysis of esters and derivatization of the acid moiety. The minimal detectable amount was found to be 0.15 pg with the use of an ECD. 

Pentazocine, cyclazocine and related drugs, prior to analysis, were converted into pentafluorobenzyl ethers [543,544] or TMS derivatives [545]. The former make the determination of pentazocine possible at concentrations down to 1 ng/ml in human plasma. The method involves a several step extraction. 

The aldehyde is trapped with high volume samplers suspended in mid-canopy drawing 25 - 30 m /hr of air through a bed of 20 g of Amberlite XAD-2 resin. Originally the pheromone was derivat-ized to the pentafluorobenzyl oxime after solvent extraction from the resin (8). This was followed by silica gel column clean-up and quantitation by capillary GC with electron capture detection. This gave satisfactory results but was tedious and expensive. 

Cullere, L., Cacho, J., and Ferreira, V. (2004a). Analysis for wine C5-C8 aldehydes through the determination of their 0-(2,3,4,5,6-pentafluorobenzyl)oximes formed directly in the solid phase extraction cartridge. Anal. Chim. Acta, 524, 201-206. 

Xiao, X.-Y. McCaUey, D.V. McEvoy, J. Analysis of estrogen in river water and effluents using solid-phase extraction and gas chromatography-negative chemical ionisation mass spectrometry of the pentafluorobenzyl derivatives. J. Chromatogr., A 2001, 923, 195-204. 

Table 1.6 Principal ions produced by CID experiments of diacetyl mono-PFB-oxime [M + H]+ (m/z 282), acetoin PFB-oxime [M + H—18]+ (m/z 266), and o-chlorobenzaldehyde PFB-oxime [M + F1]+ (m/z 336) precursor ions. Collision gas Fie (dumping gas flow 0.3mL/min). Flamini et al., (2005) Monitoring of the principal carbonyl compounds involved in malolactic fermentation of wine by synthesis of 0-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine derivatives and solid-phase-micro-extraction positive-ion-chemical-ionization mass spectrometry analysis, Journal of Mass Spectrometry, 40, p. 1561. Copyright John Wiley Sons, Ltd. Reproduced with permission. 

For the determination of benzoylecgonine from plasma, the compound was extracted after basification (pH 9.5) with ethanol-chloroform (20 80), then it was immediately reacted with pentafluorobenzyl bromide and the pentafluorobenzyl-benzoylecgonine partitioned into a nonpolar solvent (benzene) leaving the more polar interfering substances behind. This is the important step in the procedure. 

---