Gas Liquid Chromatographic Determination of Acetaminophen in Blood Plasma

Abstract

An improved procedure for the GLC determination of acetaminophen (N-acetyl-p-aminophenol) in the presence of N-butyryl-p-aminophenol (internal standard) is described. The method is based on the extraction of acetaminophen from plasma with ethyl acetate containing a known amount of N-butyryl-p-aminophenol. Following a clean-up step with a basic buffer solution and neutralization with acid, both compounds are reextracted into ethyl acetate. The ethyl acetate is evaporated to dryness and the residue dissolved in 5 μl of pyridine and 15 μl of acetic anhydride at 42°C. One to 2 μl samples are injected directly into the gas chromatograph. This extraction process does not give rise to troublesome interfering peaks in the chromatogram. In addition, it prevents late-eluting peaks which inhibit efficient processing of samples. The recovery of acetaminophen is approximately 54%, and the limit of quantitation 0.5 μg/ml of plasma. Data are presented to illustrate the practicality of the method for bioavailability evaluation from acetaminophen plasma levels after oral administration of 325 mg of an acetaminophen dosage form.     

Separation and determination of tocopherols in vegetable oils by solid phase extraction on porous polymers SPE cartridges and capillary gas chromatography analysis

In this study we present the solid phase extraction selectivity of tocopherols from vegetable oils using four porous polymers (Porapak P, Porapak Q, Porapak QS, Porapak N). The tocopherols elution from SPE cartridges was performed using several hexanes:ethyl acetate mixtures (100:0, 95:5, 90:10, 85:15, v/v). Tocopherols (α, γ and δ-tocopherol) were analyzed by gas chromatography without any derivation steep. The amount of NaOH used for triglyceride removal was optimized. Particularly liquid-liquid and solid phase extraction methods for the extraction of tocopherols from vegetable oils were compared. The results confirmed that porous polymers represent promising SPE alternatives for the extraction of tocopherols from oils.     

Quantitation of SR 27417 in human plasma using electrospray liquid chromatography-tandem mass spectrometry: A study of ion suppression

The effect of coeluting matrix compounds on the quantitation of SR 27417 in human plasma using electrospray liquid chromatography-tandem mass spectrometry has been examined. During the method development stage of this assay, plasma samples spiked with the analyte at 100 pg/mL were extracted using three different procedures: a hexane liquid-liquid extraction, an ethyl acetate back-extraction, and a solid phase extraction. Ion intensity of the analyte was found to be related inversely to the percent ionization of coeluting matrix components as evidenced by full scan spectra. The ethyl acetate back-extraction, which contained the fewest coeluting components, resulted in the highest ion intensity for the analyte. An assay comparison was done by using the liquid-liquid hexane and the ethyl acetate back-extractions for sample preparation. Replicate 1-mL samples (n=5) at 11 concentrations from 5 to 2000 pg/mL were extracted and analyzed. The results for the ethyl acetate back-extracted samples were acceptable from 2000 to 5 pg/mL with accuracy ranging from ?11.6 to 2.61% of the nominal concentrations. In contrast, the hexane liquid-liquid method had poor accuracy and precision below 20 pg/mL. The difference is explained by suppression of analyte ion intensity. These results are consistent with the current theory of electrospray ionization.     

Screening Procedure for Sodium Fluoroacetate (Compound 1080) at Sub-microgram/gram Concentrations in Soils

Abstract

Sodium fluoroacetate (Compound 1080) is readily quantitated at sub-microgram per gram concentrations in small (ca. 1 g) soil samples. Samples are ultrasonically extracted with water, which is then partitioned with hexane, and acidified prior to re-extraction with ethyl acetate. The latter is taken to dryness in the presence of triethanolamine “keeper”, and the resulting acid is derivatized with pentafluorobenzyl bromide. Quantitation is performed using a gas chromatograph equipped with an electron-capture detector. A standardized statistical protocol is used to validate a screening level of 0.2 μg Compound 1080/g soil. Difluoroacetic, trifluoroacetic, and naturally-occurring formic acids do not interfere with the determination. The recovery for Compound 1080 was 40% from soil fortified to 0.2 μg/g soil.     

Candida antarctica lipase A in the dynamic resolution of novel furylbenzotiazol-based cyanohydrin acetates

A series of novel (R)-furylbenzotiazol-based cyanohydrin acetates were prepared in over 90% isolated yields from the corresponding furancarbaldehydes. The one-pot method combines a basic resin to produce hydrogen cyanide from acetone cyanohydrin, an equilibrium between the formation and decomposition of furylbenzotiazol-based cyanohydrins and the unique enantioselectivity of Candida antarctica lipase A, allowing the acylation of (R)-cyanohydrins in the presence of vinyl acetate in anhydrous acetonitrile.     

Liquid Chromatography–Electrospray Ionization–Mass Spectrometric Method for the Determination of Hydrochlorothiazide in Human Plasma: Application to a Pharmacokinetic Study

Abstract

A rapid, convenient, and sensitive liquid chromatography–electrospray ionization–mass spectrometry method was developed and validated for the quantification of hydrochlorothiazide in human plasma. The samples were first spiked with the internal standard, and the analyte was then extracted with ethyl acetate. The chromatographic separation was achieved on a C₁₈ column by using water–acetonitrile (68:32, v/v) as mobile phase. The method was linear within the range of 2.5–200 ng/ml. The lower limit of quantification was 1.0 ng/ml. Finally, the validated method was successfully applied for the evaluation of the pharmacokinetic profiles of hydrochlorothiazide in healthy male Chinese volunteers.     

Evaluation of Extraction Procedures of Organochlorine Pesticides from Natural Waters and Sediments

Abstract

This study aims to evaluate different procedures for the extraction of organochlorine pesticides (OCP's) from natural waters and sediments. In the case of extraction from water, a C18 disk solid-phase extraction method was employed. Recovery experiments in the range of 40 to 200 ng/l with selected organochlorine compounds resulted in average recoveries between 80 and 100%. Four different solvents, hexane, ethyl acetate, acetonitrile and methanol, were tested as eluting agents. Best recoveries were obtained with ethyl acetate and hexane. A comparative study of OCP sediment extraction procedures was performed employing sonication, Soxhlet extraction and shake-flask methods. The capacity of these methods to recover OCP's from a sediment sample fortified at 50 ng/g was evaluated using hexane : acetone (1:1 v/v), hexane: acetone (8:2 v/v), acetonitrile and dichlorometane. The three extraction techniques gave similar results and dichloromethane was the most effective solvent. The optimised methods were applied in the analysis of waters and sediments from the “Aiguamolls de l'Empordà” Nature Park, Girona (Spain).     

Rapid determination of bisphenol A in drinking water using dispersive liquid‐phase microextraction with in situ derivatization prior to GC‐MS

This paper described a novel approach for the determination of bisphenol A by dispersive liquid‐phase microextraction with in situ acetylation prior to GC‐MS. In this derivatization/extraction method, 500 μL acetone (disperser solvent) containing 30.0 μL chlorobenzene (extraction solvent) and 30.0 μL acetic anhydride (derivatization reagent) was rapidly injected into 5.00 mL aqueous sample containing bisphenol A and K₂CO₃ (0.5% w/v). Within a few seconds the analyte was derivatized and extracted at the same time. After centrifugation, 1.0 μL of sedimented phase containing enriched analyte was determined by GC‐MS. Some important parameters, such as type and volume of extraction and disperser solvent, volume of acetic anhydride, derivatization and extraction time, amount of K₂CO₃, and salt addition were studied and optimized. Under the optimum conditions, the LOD and the LOQ were 0.01, 0.1 μg/L, respectively. The experimental results indicated that there was linearity over the range 0.1–50 μg/L with coefficient of correlation 0.9997, and good reproducibility with RSD 3.8% (n = 5). The proposed method has been applied for the analysis of drinking water samples, and satisfactory results were achieved.     

Chromatographic properties and polarity evaluation of poly(1-trimethylsilyl-1-propyne) and poly(1-phenyl-1-propyne)

The chromatographic properties of poly(1-trimethylsilyl-1-propyne) (PTMSP) and poly(1-phenyl-1-propyne) (PPP) were studied by gas chromatography using packed columns. The selectivity and efficiency of columns packed with PTMSP and PPP were compared to the data obtained for columns with other known adsorbents and stationary phases. The McReynolds and Rohrschneider constants, on the basis of which the polarity of the new phases was evaluated, were calculated. The results of the investigation of chromatographic properties allow PTMSP to be brought in line with the polymeric adsorbents Porapak Q, Porapak QS, and Chromosorb 106, while PPP, with the methyphenylsilicon phases SE-52 and OV-3.     

Practical Oxirane Ring Opening with In Situ Prepared LiCN; Synthesis of (2S,3R)-3-(2,4-Difluorophenyl)-3-hydroxy-2-methyl-4-(1H-1,2,4-triazol-1-yl)-1-butanenitrile

Trisubstituted oxirane 1 was regiospecifically opened with LiCN in situ prepared from acetone cyanohydrin and LiH to provide the corresponding β-hydroxy nitrile 2 in satisfactory yield, enabling us to manufacture a key intermediate for a new antifungal agent on a multi-kg scale. Some applications of this method to the ring opening of other oxiranes and nucleophilic substitution are also described.     

A Simple Electrochemical Method for the Quantitative Determination of Acetaminophen in Serum

Abstract

A simple electrochemical method for the determination of acetaminophen in serum is described. The eleotrode and associated electronics are simple, reliable, and inexpensive to build. The apparatus can be operated at a rate of 2–3 determinations per minute using only 10 μl serum per determination. The procedure includes extraction of acetaminophen in ethyl acetate and subsequent oxidative amperometric detection of the drug by a form of flow-injection analysis. The system parameters of buffer, pH, and redox potential have been optimized to permit measurement of less than 10 μg/ml of acetaminophen. The determination is linear over the range of 10–300 μg/ml with a C.V. of less than 3% for replicate analysis of the same sample.     

Development of a new stir bar sorptive extraction coating and its application for the determination of six pesticides in sugarcane juice

In this article, a novel polydimethylsiloxane/activated carbon (PDMS‐ACB) material is proposed as a new polymeric phase for stir bar sorptive extraction (SBSE). The PDMS‐ACB stir bar, assembled using a simple Teflon^®/glass capillary mold, demonstrated remarkable stability and resistance to organic solvents for more than 150 extractions. The SBSE bar has a diameter of 2.36 mm and a length of 2.2 cm and is prepared to contain 92 μL of polymer coating. This new PDMS‐ACB bar was evaluated for its ability to determine the quantity of pesticides in sugarcane juice samples by performing liquid desorption (LD) in 200 μL of ethyl acetate and analyzing the solvent through gas chromatography coupled with mass spectrometry (GC‐MS). A fractional factorial design was used to evaluate the main parameters involved in the extraction procedure. Then, a central composite design with a star configuration was used to optimize the significant extraction parameters. The method used demonstrated a limit of quantification (LOQ) of 0.5–40 μg/L, depending on the analyte detected; the amount of recovery varied from 0.18 to 49.50%, and the intraday precision ranged from 0.072 to 8.40%. The method was used in the analysis of real sugarcane juice samples commercially available in local markets.     

Rapid,automatic, high-precision method for micro,ultramicro, and trace determinations of sulfur

Samples are burned in a Carlo Erba 1106 elemental analyzer over copper oxide with oxygen, injected into the carrier gas. Combustion gases are reduced with copper. Water is absorbed, and sulfur dioxide is separated from carbon dioxide and nitrogen in a very short column of Porapak QS. Sample size is upt ot 0.7 mg, one determination takes 5 min, and the sampler takes up to 196 samples. It can be continuously loaded, and the instrument can be left to work automatically overnight. For the micro determination, helium is the carrier gas, and sulfur dioxide is measured with a thermal conductivity detector. The standard deviation of 18 analyses of pure organic compounds was 0.0446% S. The detection limit is 0.5 μg S, or about 0.1% S in a normal 0.5-mg sample. For ultramicro and trace determination, nitrogen is the carrier gas, and the measurement is made with an electron capture detector. The detection limit is 0.002 μg S, or about 0.0004% (4 mg kg^?1 S) in a normal 0.5-mg sample.     

An Extraction Method to Quantitate Serotonin in Human Serum,Amniotic Fluid and Urine Samples by HPLC Using 6-Hydroxy Tryptamine as Internal Standard

Abstract

A method for extracting serotonin (5-HT) from human serum, amniotic fluid and urine samples is described. A mixture of sample, 6-hydroxy tryptamine (6-HT) as internal standard and sodium carbonate is extracted with ethyl acetate. The ethyl acetate layer is mixed with 200 ul of triethylamine phosphate buffer (pH 3.0) used for mobile phase and centrifuged. An aliquot of the aqueous layer was used for HPLC quantitation with amperometric detection. With this method 30 samples can be assayed in 6 hours.     

Use of a Drying Cartridge in On-Line Solid-Phase Extraction–Gas Chromatography–Mass Spectrometry

A drying cartridge was used and optimized for the in-line elimination of water from the desorption eluent in on-line solid phase extraction–gas chromatography (SPE–GC). The cartridge is essentially a small stainless-steel precolumn packed with a drying agent which can be regenerated by simultaneous heating and purging with a moisture-free gas. The drying cartridge was mounted on an additional valve instead of between the SPE–GC transfer valve and the on-column injector to enable regeneration of the cartridge during the GC run and, thus, to increase sample throughput. Three drying agents were tested, viz. sodium sulfate, silica, and molecular sieves. Although molecular sieves have the highest capacity, silica was preferred because of practical considerations. Large-volume injections were performed through the in-line drying cartridge using a mixture of 23 microcontaminants ranging widely in polarity and volatility. Four solvents were tested. With pentane and hexane, the more polar analytes were retained by the drying cartridge. Ethyl acetate and methyl acetate gave much better (and closely similar) recoveries for all analytes. Because water elimination on the silica cartridge proved to be less critical than with ethyl acetate, this solvent was finally selected. The entire SPE–drying cartridge–GC set-up was combined with mass spectrometric (MS) detection for the determination of a mixture of micropollutants in real-life water samples. With 10-ml tap water samples spiked at the 0.5 μg/l level, for the majority of the test compounds the analyte recoveries generally were 60–106%, and (full-scan) detection limits typically were 0.01–0.03 μg/l. Some very polar analytes such as, e.g. dimethoate, were (partially) sorbed onto the silica packing of the drying cartridge.     

Development of a New α‐Aminonitrile Synthesis

Abstract

α‐Aminonitriles are prepared upon reaction of aryl carboxaldehydes with LiHMDS and acetone cyanohydrin. This new method provides a general route to the synthesis of various substituted α‐amino‐arylacetonitriles in high yield and purity, and avoids the use of the highly toxic cyanide salts.     

Biocatalytic enantioselective preparation of phenothiazine-based cyanohydrin acetates: kinetic and dynamic kinetic resolution

Dynamic kinetic resolution is used for the preparation of a series of novel (+)-10-alkyl-phenothiazin-3-ylcyanomethyl acetates. The method exploits a basic resin both for the racemization and formation of phenothiazine-based cyanohydrins and for the decomposition of acetone cyanohydrin in one pot together with Candida antarctica lipase A-catalyzed enantioselective acylation with vinyl acetate in acetonitrile. The Candida antarctica lipase A-catalyzed methanolysis of racemic 10-alkyl-phenothiazin-3-ylcyanomethyl acetates in acetonitrile with E?100 leads to the corresponding (−)-acetates.     

Dispersive Liquid‐Liquid Microextraction of Cu(II) Using a Novel Dioxime for Its Highly Sensitive Determination by Graphite Furnace Atomic Absorption Spectrometry

A dispersive liquid‐liquid microextraction (DLLME) technique was proposed for the enrichment and graphite furnace atomic absorption spectrometric (GFAAS) determination of Cu²⁺ in water samples. In this method a mixture of 480 μL acetone (disperser solvent) containing 26 μg S,S‐bis(2‐aminobenzyl)‐dithioglyoxime (BAT) ligand and 20 μL carbon tetrachloride (extraction solvent) was rapidly injected by a syringe into 5 mL aqueous sample containing copper ions (analyte). Thereby, a cloudy solution formed. After centrifugation, the fine droplets containing the extracted copper complex were sedimented at the bottom of the conical test tube. This phase was collected by a microsyring and after dilution by methanol, 20 μL of it was injected into the graphite tube of the instrument for analysis. Effects of some parameters on the extraction, such as extraction and disperser solvent type and volume, extraction time, salt concentration, pH and concentration of the chelating agent were optimized. The response surface method was used for optimization of the effective parameters on the extraction recovery. Under these conditions, an enrichment factor of 312 was obtained. The calibration graph was linear in the rage of 2–50 μ L⁻¹ Cu²⁺ with a detection limit of 0.03 μg L⁻¹ and a relative standard deviation (RSD) for five replicate measurements of 3.4% at 20 μg L⁻¹ Cu²⁺. The method was successfully applied to the determination of Cu²⁺ in some spring water samples.     

Development of an Enzyme Immunoassay for the Determination of the Herbicide Metsulfuron-Methyl Based on Chicken Egg Yolk Antibodies

Abstract

The development of an indirect competitive enzyme immunoassay for the sulfonylurea herbicide metsulfuron-methyl (MSM) is described. In contrast to traditional antibody generation in mammals, this extremely sensitive method is based on chicken egg yolk antibodies (IgY). They were raised in laying hens using an MSM-derivative-BSA hapten as immunogen. With a 1:10000 dilution of the antibody solution and a coating antigen (MSM-derivative-KLH) concentration of 10 μg L^?1 the IC₅₀ value achieved for the target analyte was 0.4 μg L^?1. The least detectable dose was established at 13 ng L^?1. Cross-reactivity was tested with 5 structurally related compounds, where only sulfometuron showed a significant binding. The ELISA was tested with spiked tap and surface water samples. This paper, for the first time, demonstrates the production of high-affinity IgY antibodies for a herbicide compound.     

A Simple HPLC Method for the Determination of Trazodone Human Serum

Abstract

A simple HPLC method with minimal sample preparation and good reproducibility for the determination of trazodone in serum is described. Basified serum samples were extracted using ethyl acetate containing diazepam as the internal standard (IS). Chromatography was performed on a cyanopropylsilane column with 15 μL sample injection. The mobile phase consisted of 0.02 M ammonium phosphate, pH 7.5 : acetonitrile (70:30 v/v). The eluent was monitored at 220 nm. The serum standard curve was linear from 10.0 to 8000.0 ng/mL serum. The overall within-run quality control CV was 6.3% for five concentrations (20.0, 40.0, 100.0, 250.0 and 1000.0 ng/mL) and the overall recovery from serum was 85.4%. This method has been applied to the analysis of human serum samples.