Simultaneous determination of cocaethylene and cocaine in blood by gas chromatography with surface ionization detection

Summary Cocaethylene together with cocaine spiked in human whole blood has been found measurable at high sensitivities by capillary gas chromatography with surface ionization detection. The drugs could be rapidly extracted by Sep-Pak C₁₈ cartridges with recovery of more than 60%. The calibration curves for both cocaethylene and cocaine using cocapropylene as internal standard were linear in the range 50–300 pmol mL⁻¹ of whole blood. The detection limits of cocaethylene and cocaine were 5–10 pmol mL⁻¹ (0.1–0.2 pmol on column if recovery is 100%). Cocaethylene could be determined for whole blood obtained from rats (ca. 200 g body wt.), which had received subcutaneous injection of 10 mg cocaine hydrochloride and 2.0 mL of 30% (v/v) ethanol 3 h before sampling; the mean levels of cocaethylene and cocaine were 101 and 1230 pmol mL⁻¹, respectively.     

Separation ofN-carbamoyl aspartate andl-dihydroorotate from serum by high-performance liquid chromatography with fluorimetric detection

Summary A high-performance liquid chromatographic method, with 9-anthryldiazomethane as derivatizing agent, has been developed for the simultaneous determination ofN-carbamoyl aspartate andl-dihydroorotate in serum. Sample preparation for 1 mL serum was by simple liquid-liquid extraction and then derivatization. The compounds were separated on a Luna C18(2) column by use of a gradient prepared from acetonitrile and 10 mM sodium acetate buffer, pH 6.0, and fluorimetric detection was performed at excitation and emission wavelengths of 365 nm and 412 nm, respectively. The response was found to be linearly dependent on concentration between 0.8 and 60 μg mL⁻¹ forl-dihydrooratate and between 0.9 and 90 μg mL⁻¹ forN-carbamoyl aspartate; the mean recovery rates were 50 and 51%, respectively. The limits of detection and quantification were 0.33 μg mL⁻¹ and 0.6 μg mL⁻¹, respectively, forl-dihydroorotate and 0.4 μg mL⁻¹ and 0.7 μg mL⁻¹ forN-carbamoyl aspartate. This method can be used to assess accumulation ofN-carbamoyl aspartate andl-dihydroorotate in body fluids in situations where cellular pyrimidine de novo synthesis is impaired.     

Determination of butyltin and octyltin stabilizers in poly(vinyl chloride) products by headspace solid-phase microextraction and gas chromatography with flame-photometric detection

Headspace solid-phase microextraction (HS-SPME) and gas chromatography with flame photometric detection (GC-FPD) have been investigated for determination of butyltin and octyltin stabilizers in poly(vinyl chloride) (PVC) products. The organotin stabilizers were first released from the plastic matrix by dissolving the PVC sample in tetrahydrofuran (THF). The stabilizers were then hydrolyzed to the chloride forms, by treatment with 6 mol L⁻¹ HCl, then derivatized with sodium tetraethylborate (NaBEt₄) in 0.2 mol L⁻¹ sodium acetate buffer (pH 4.5) at 50 °C. HS-SPME was performed with a fused-silica fiber coated with a 100-μm film of polydimethylsiloxane (PDMS). The collected organotin compounds were then desorbed in the GC injector at 280 °C and analyzed by GC-FPD. Linearity (r≥0.994) over a concentration of approximately two orders of magnitude was usually obtained. Limits of quantitation (LOQ) of the four organotin compounds studied, viz., monobutyltin (MBT), dibutyltin (DBT), monooctyltin (MOT), and dioctyltin (DOT), were in the range 0.3–1.0 ng Sn mL⁻¹. Recovery was >90% for butyltins and >80% for octyltins. The method was validated by analyzing two reference standard PVC sheets with known organotin content. The applicability of the method to analysis of organotin stabilizers in commercial PVC products was also demonstrated.     

Development and validation of an HPLC method for the simultaneous determination of clozapine and desmethylclozapine in plasma of schizophrenic patients

Summary A high-performance liquid chromatographic method with amperometric detection has been developed for the determination of levels of clozapine (CLZ) and its active metabolite N-desmethylclozapine (DMC) in human plasma. The analysis was performed on a 5 μm C8 reversed phase column (150×4.6 mm i.d.), with acetonitrile-phosphate buffer (pH 3.5), as the mobile phase. The detection voltage was +800 mV and the cell and column temperature were 50°C. Linear responses were obtained between 2 ng mL⁻¹ and 100 ng mL⁻¹. Absolute recovery for both clozapine and desmethylclozapine exceeded 88% and the detection limit was 1 ng mL⁻¹. Repeatability, intermediate precision and accuracy were satisfactory. The method, which is rapid, sensitive and selective, has been applied to therapeutic drug monitoring in schizophrenic patients following administration of Leponex^? tablets. In 21 patients in steady state at a mean daily clozapine dosage of 358 mg (ranging from 150 to 500 mg day⁻¹), clozapine levels averaged 379 ng mL⁻¹ (ranging from 102 to 818 ng mL⁻¹) and DMC levels averaged 233 ng mL⁻¹ (ranging from 70 to 540 ng mL⁻¹). The method requires only a very small amount of plasma (100 μL), and thus it is suitable for pharmacokinetic studies, as well as for therapeutic drug monitoring.     

Validated HPLC–MS–MS method for simultaneous determination of atorvastatin and 2-hydroxyatorvastatin in human plasma—pharmacokinetic study

Cholesterol-reducing statin drugs are the most frequently prescribed agents for reducing morbidity and mortality related to coronary heart disease. In this publication a validated, highly sensitive, and selective isocratic HPLC method is reported for quantitative determination of the major statin drug atorvastatin (ATV) and its metabolite 2-hydroxyatorvastatin (HATV). Detection was performed with an electrospray ionization triple-quadrupole mass spectrometer equipped with an ESI interface operating in positive-ionization mode. Multiple reaction monitoring (MRM) was used for MS–MS detection. The calibration plot was linear in the concentration range 0.10–40.00 ng mL⁻¹ for both ATV and HATV. Inter-day and intra-day precision and accuracy of the proposed method were characterized by measurement of relative standard deviation (RSD) and percentage deviation, respectively; both were less than 8% for both analytes. The limit of quantitation was 0.02 ng mL⁻¹ for ATV and 0.07 ng mL⁻¹ for HATV. The method was used for pharmacokinetic study of ATV and HATV. Pharmacokinetic data for all analytes are also reported.     

Potential of microcolumn liquid chromatography and capillary electrophoresis with flame photometric detection for determination of polar phosphorus-containing pesticides

Summary The potential of microcolumn liquid chromatography (μlC) and capillary electrophoresis (CE) with on-line, flame photometric detection (FPD) in the P-selective mode has been studied for determination of polar P-containing pesticides, glyphosate and its main metabolite, aminomethylphosphonic acid (AMPA), ethephon, fosetyl-aluminium and acephate. Acephate was determined by reversed-phase μLLC-FPD using large-volume injections with peak compression, the other compounds were determined by μLC-FPD and CE-FPD using simple, large-volume injection procedures to obtain limits of detection of 7.5-500 ng·mL⁻¹ and 1.0 μ·mL⁻¹, respectively. The methods showed acceptable repeatability and robustness and were successfully applied for rapid and selective determination of pesticides in fruit, vegetable and water samples.     

Separation and determination of rutin and quercetin in the flowers ofSophora japonica L. by capillary electrophoresis with electrochemical detection

Summary Capillary electrophoresis with amperometric detection has been evaluated for the simultaneous determination of rutin and quercetin. The cyclic voltammogram, hydrodynamic voltammogram, and the effects of pH, concentration of buffer and sodium dodecyl sulfate (SDS), and amount of organic modifier on the separation and the detection were studied. The optimized conditions were: detection potential 1.2V, separation at 12 kV, 5 s at 15 kV for sample injection, running electrolyte 20 mmol L⁻¹ borate buffer, pH 8.8, containing 40 mmol L⁻¹ SDS and 10% acetonitrile. The detection limit of the method was low, 0.001 and 0.0005 mg mL⁻¹, for rutin and quercetin, respectively; the linear ranges were wide −0.005–0.5 and 0.005–0.4 mg mL⁻¹, respectively. The variations in peak current and migration time for eight consecutive injections of a standard solution containing 0.1 mg mL⁻¹ of each compound were 4.78 and 3.63%, and 6.50 and 2.59% for rutin and quercetin, respectively. The levels of the two compounds in traditional Chinese herbal drugs were easily determined.     

Growth and characterization of Mn- and Co-doped ZnO nanowires

A flow injection chemiluminescence method is proposed for the determination of cobalt, based on the strong catalytic effect of Cobalt(II) (1,10-phenanthroline)₃ complex on the lucigenin-periodate reaction in alkaline medium. Under the optimum experimental conditions, the chemiluminescence signal responded linearly to the concentration of cobalt(II) in the 1.0 × 10⁻⁹–3.0 × 10⁻⁷ g mL⁻¹ range with a detection limit of 4.4 × 10⁻¹⁰ g mL⁻¹ cobalt(II). The relative standard deviation for the determination of 5.0 × 10⁻⁸ g mL⁻¹ of cobalt was 2.3% in eleven replicated measurements. The method was successfully applied to the determination of cobalt(II) in pharmaceutical preparations.     

Analysis of 5-hydroxy-N-methyl-2-pyrrolidone and 2-hydroxy-N-methylsuccinimide in plasma

Summary A method for the determination of 5-hydroxy-N-methyl-2-pyrrolidone (5-HNMP) and 2-hydroxy-N-methylsuccinimide (2-HMSI) in plasma was developed. 5-HNMP and 2-HMSI are metabolites to the widely used organic solvent N-methyl-2pyrrolidone (NMP). The 5-HNMP and 2-HMSI were purified from plasma by C8 solid phase extraction, derivatised by bistrimethylsilyl trifluoroacetamid, and analysed by gas chromatography with mass spectrometric detection. For 5-HNMP, the precision was 2–7 % (120 and 780 ng mL⁻¹) and the detection limit was 6 ng mL⁻¹ (m/z 98). For 2-HMSI, the precision was 2–9 % (160 and 1000 ng mL⁻¹) and the detection limit was 4 ng mL⁻¹ (m/z 144). The method is applicable for analysis of plasma samples from workers exposed to NMP.     

Quantitative analysis of temazepam in plasma by capillary gas chromatography: Application to pharmacokinetic studies in rats

Summary A sensitive method was developed for the determination of temazepam in plasma using capillary gas chromatography. After the extraction into dichloromethane-pentane (1∶1), temazepam was quantitated as its O-trimethylsilyl derivative on a capillary column with a⁶³Ni electron capture detector using prazepam as internal standard. The detector response was found to be linear in the concentration range 0.031 to 8 μg mL⁻¹. The detection limit was about 3.5 ng mL⁻¹. The intraday and inter-day coefficients of variation were below 9%. The method was used to determine the pharmacokinetic profile of temazepam in rats after intravenous administration.     

Determination of rutin and forsythin in fruit ofForsythia suspensa(Thunb.) Vahl by capillary electrophoresis-electrochemical detection

Summary Capillary electrophoresis-amperometric detection is evaluated for simultaneous determination of rutin and forsythin. The cyclic voltammogram, hydrodynamic voltammogram, effect of pH, buffer concentration and SDS, and percent organic modifier on separation and detection were studied. Conditions were optimized as follows: 1.2 V detection potential; separation at 12 kV; 5 s at 15 kV for sample injection time and sample injection voltage; mobile phase 20 mM boric acid buffer; pH 8.4, containing 40 mM SDS and 10% (v/v) acetontrile. The method gave low detection limit as 0.001 mg mL⁻¹ and 0.0005 mg mL⁻¹ (S/N=3), wide linear range 0.005–0.5 mg mL⁻¹ for rutin and forsythin, respectively. The relative standard deviations of peak current and migration time for 8 consecutive injections of the standard solution containing 0.1 mg mL⁻¹ each compound were 4.78%, 3.63% and 6.40%, 2.95% for rutin and forsythin, respectively. In addition, levels of the two compounds in traditional Chinese herbal drugs were easily determined.     

Diol sep-pak cartridges for enrichment of polychlorobiphenyls and chlorinated pesticides from water samples; determination by GC-ECD

Summary Gas chromatography of polychlorinated biphenyls and chlorinated pesticides in water samples has been performed after adsorption from a 20–200-mL sample on to a cartridge containing 100 mg diol-bonded porous silica. The PCBs are desorbed with 500 μL ethyl acetate, which is concentrated and analysed by gas chromatography with electron-capture detection (GC-ECD). The average recovery of 0.1 ng mL⁻¹ PCB congeners from distilled water and from Aniene river water is≥95% (standard deviation≤2.8). Average recoveries of 25 ng mL⁻¹ Aroclor 1254 from distilled water and from Aniene river water were, respectively, 94.4% and 92.5% (standard deviation 5.8). In the separation of PCB congeners from the chlorinated pesticides only the aldrin (40%) was eluted with the PCBs from the diol Sep-Pak cartridge by aqueous methanol. The method described is simple and reproducible.     

Simultaneous separation and determination of Cu(II), Fe(III), and Pb(II) by reversed-phase ion-pair chromatography withN,N,N′, N′-ethylene-diaminetetrakis(methylenephosphonic Acid)

Summary A reversed-phase ion-pair chromatographic (RPIPC) method withN,N,N′, N′-ethylenediaminetetrakis(methylenephosphonic acid) (EDTMP) as coordinating agent has been developed for simultaneous separation and detection of Cu(II), Fe(III), and Pb(II) ions. Response is linearly dependent on amount of sample over the range 9.52–50.8 μg mL⁻¹ for Cu(II), 8.31–41.8 μg mL⁻¹ for Fe(III), and 37.3–51.8 μg mL⁻¹ for Pb(II). The method has been applied successfully to an artificial mixed-ore sample.     

Improved HPLC determination of fluoxetine and norfluoxetine in human plasma

Summary An HPLC method with fluorescence detection has been developed for the determination of fluoxetine and its main metabolite norfluoxetine in human plasma. Pretreatment of the biological samples by liquid-liquid extraction was used to improve the sensitivity of a previously published SPE procedure. The method uses 200 μL plasma and recovery is good for both analytes. On a C₈ column with a mixture of perchlorate buffer and acetonitrile as mobile phase fluoxetine, norfluoxetine and the internal standard (paroxetine) were eluted in less than 9 min, without interference from the biological matrix. Response for both analytes was linearly dependent on concentration over the range 2.5–500 ng mL⁻¹, and repeatability (RSD%) was <4%. The limit of detection was 1 ng mL⁻¹ for both fluoxetines. Application to plasma samples from depressed patients treated with fluoxetine gave good results. There was no interference from other common CNS drugs. This method seems to be a useful tool for clinical monitoring, because it requires small plasma samples and is highly sensitive and highly selective.     

Determination of triazine herbicides in human body fluids by solid-phase microextraction and capillary gas chromatography

Summary Eight triazine herbicides, prometon, propazine, atrazine, simazine, prometryn, ametryn, metribuzin, and cyanazine, have been extracted from human whole blood and urine samples by headspace solid-phase microextraction (SPME) with a polydimethylsiloxane-coated fiber and quantified by capillary gas chromatography with nitrogen-phosphorus detection. Extraction efficiencies for all compounds were 0.21–0.99% for whole blood, except for cyanazine (0.06%). For urine, the extraction efficiencies for prometon, propazine, atrazine, prometryn and ametryn were 13.6–38.1%, and those of simazine, metribuzin and cyanazine were 1.35–8.73%. The regression equations for the compounds extracted from whole blood were linear within the concentration ranged 0.01–1 μg (0.5 mL)⁻¹ for prometon, propazine, atrazine, prometryn, and ametryn, and 0.02–1 μg (0.5 mL)⁻¹ for simazine, metribuzin, and cyanazine. For urine, regression equations for all compounds were linear within the concentration range 0.005–0.25 μg mL⁻¹. Compound detection limits were 2.8–9.0 ng (0.5 mL)⁻¹ and 0.4–2.0 ng mL⁻¹ for whole blood and urine, respectively. The coefficients of within-day and day-to-day variation were satisfactory for all the compounds, and not greater than 10.3 and 14.2%, respectively. Data obtained from determination of atrazine in rat whole blood after oral administration of the compound are also presented.     

Development of Electro Solid-Phase Microextraction and Application to Methamphetamine Analysis

A new electro solid-phase microextraction (El-SPME) technique using homemade pencil-lead fibers has been developed as an effective means of selective extraction of methamphetamine before analysis by gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS). The methamphetamine was extracted by use of a laboratory-made El-SPME cell with three electrodes—the pencil-lead SPME fiber, Ag/AgCl, and platinum as working, reference, and auxiliary electrodes, respectively. A negative potential was applied to the homemade pencil-lead fiber during extraction. Experimental conditions, for example type of pencil-lead fiber, conditions for modification of the fiber, extraction time, applied potential, pH, and gas chromatographic conditions were optimized. Methamphetamine was identified by GC–MS. Screening of the extracted compounds showed that the proposed El-SPME technique is much more selective than direct SPME using a commercially available polyacrylate fiber. Under the optimum conditions the calibration plot for the compound was linear in the range 50–3,200 ng mL⁻¹ and the detection limit was 34 ng mL⁻¹.     

Selective solid-phase extraction of trace Fe(III) from biological and natural water samples using nanometer SiO2 modified with acetylsalicylic acid

A new method using acetylsalicylic acid (aspirin) modified SiO₂ nanoparticles (nanometer SiO₂-aspirin) as a solid-phase extractant (SPE) has been developed for the preconcentration of trace amounts of Fe(III) prior to their determination by inductively coupled plasma optical emission spectrometry. The preconcentration conditions of analytes were investigated, including the pH value, the shaking time, the mass of sorbent, the sample flow rate and volume, the elution condition and the interfering ions. At pH 4, the sorption capacity of nanometer SiO₂-aspirin was found to be 1.28 mmol g⁻¹. The preconcentration factor is 50. The detection limit (3σ) for Fe(III) was 0.49 ng mL⁻¹. The method was validated by analyzing two certified reference materials (GBW 08301, river sediment and GBW 08303, polluted farming soil), and the results obtained are in good agreement with standard values. The method was also applied to the determination of trace Fe(III) in biological and water samples with satisfactory results. Correspondence: Xiangbing Zhu, Department of Chemistry, Lanzhou University, Lanzhou 730000, P.R. China     

Sensitive determination of 3-methoxy-4-hydroxyphenylglycol (MHPG) in human plasma by HPLC with electrochemical detection

Summary This study deals with the development of a new HPLC method for the determination of 3-methoxy-4-hydroxyphenylglycol (MHPG), the main noradrenaline metabolite in human plasma. A Varian reversed-phase column (C₈; 250 mm×4.6 mm i.d.; 5 μm particles) was used as the stationary phase and an aqueous solution of citric acid, 1-octanesulfonic acid, EDTA, and methanol was used as the mobile phase. Coulometric electrochemical detection (ED) was used to obtain the highest sensitivity. Isolation of MHPG from plasma was accomplished by means of a new solid-phase extraction procedure after a protein precipitation step. The extraction yield of MHPG from plasma was very high (>97%). Linearity was observed in the 0.5–25 ng mL⁻¹ concentration range; the limit of detection was 0.2 ng mL⁻¹ and the limit of quantitation was 0.5 ng mL⁻¹. Repeatability (RSD,%) for plasma samples was found to be <3.2% and intermediate precision was <4.3%. The method was applied to the determination of MHPG in the plasma of healthy subjects under experimentally-induced psychological stress.     

Determination of olanzapine and desmethylolanzapine in the plasma of schizophrenic patients by means of an improved HPLC method with amperometric detection

Summary An improved HPLC method with electrochemical detection has been developed for the determination of olanzapine and its main metabolite, desmethylolanzapine, in human plasma. Chromatographic separation and analysis were performed on a C₈ reversed-phase column with a mixture of methanol, acetonitrile, and pH 3.7 phosphate buffer as mobile phase; 2-methylolanzapine was used as internal standard. Careful pretreatment of the plasma samples was implemented by means of solid phase extraction (SPE). Response was linearly dependent on concentration and precision was satisfactory over the concentration range 0.5–75.0 ng mL⁻¹ for both analytes. The limit of detection was 0.2 ng mL⁻¹ for both analytes. Application to plasma samples of patients treated with Zyprexa tablets gave good results. Because of its sensitivity and selectivity, and the need for small plasma samples, this method seems to be a useful tool for clinical monitoring.     

Determination of jasmonic acid in <Emphasis Type="Italic">Lemna minor</Emphasis> (L.) by liquid chromatography with fluorescence detection

A new method is described for the determination of endogenous jasmonic acid (JA) in Lemna minor plant extracts using liquid chromatography (LC) with fluorescence detection. Plant tissues were extracted and derivatised using 9-anthryldiazomethane (ADAM reagent) prepared in situ. Accuracy and precision were improved by using the internal standard dihydrojasmonic acid (dh-JA) for the correction of JA losses during sample preparation steps. Liquid chromatography–mass spectrometry (LC/MS) analysis of ADAM derivatives of JA and dh-JA confirmed that a single molecule of JA and dh-JA was coupled with one molecule of reagent. Derivatives of JA and dh-JA were separated with gradient elution on a C₁₈ reversed-phase column using acetonitrile/water as a mobile phase and detected by a fluorescence detector at excitation and emission wavelengths of 254 and 412 nm, respectively. The detection limits of JA and dh-JA were 2.9 ng mL⁻¹ and 3.7 ng mL⁻¹ per 50-μL injection. The method is reproducible and selective and yields single peaks for each compound regardless of isomer. The specificity and accuracy of the proposed LC/FD method was confirmed by liquid chromatography–TurboIon Spray tandem mass spectrometric (LC/MS/MS) analysis of free JA in Lemna minor samples under multiple reaction monitoring conditions.