Nitrogen-phosphorus Selective Detector Research Articles

Study of silica-structured materials as sorbents for organophosphorus pesticides determination in environmental water samples

A novel sorbent based on a UVM-7 mesoporous silica doped with Ti has been synthesized and used for solid-phase extraction of several organophosphorus pesticides in environmental water samples followed by gas chromatography coupled to a nitrogen-phosphorus selective detector. Thus, mesoporous silica materials doped with Ti and Fe as well as immobilized cyclodextrin silica-based supports were prepared and morphologically characterized by several techniques such as transmission electronic microscopy, nitrogen adsorption-desorption and X-ray diffraction. These sorbents were comparatively evaluated, and Ti25-UVM-7 material was selected as the best solid phase. After optimization of extraction parameters such as amount of solid-phase, type and volume of eluent, pH and ionic strength and breakthrough volume, recoveries between 81% and 104.5% were achieved, with RSD values below 7.8% and 12% for intra-day and inter-day repeatability respectively. Moreover, limits of quantification in the range 0.5–4.4 μg L−1 were achieved for all target compounds using mass spectrometry detector. In addition, the developed method was applied for analysis of real water samples and it was validated with commercial C18 cartridges. Matrix effect was demonstrated in complex environmental matrices and the good reusability of synthesized material was also proved.

Analysis of aromatic amines as N‐propoxycarbonyl derivatives by gas chromatography with nitrogen‐phosphorus selective detection

A selective and sensitive method for the analysis of aromatic amines by GC was developed. Aromatic amines were converted to their N-n-propoxycarbonyl derivatives and measured by GC with nitrogen-phosphorus selective detection (NPD) using an HP-5 fused-silica capillary column. The derivatives of the 20 aromatic amines provided excellent NPD responses, and were resolved both quantitatively and reproducibly within 15 min. The calibration curves for aromatic amines in the range 20-500 ng were linear and the detection limits at an S/N of 3 were ca. 19-139 pg injected. This method was applied successfully to combustion smoke and human urine samples, and analyzed without any interference from coexisting substances.

Organophosphorus flame retardants and plasticizers in air from various indoor environments

Eleven organophosphorus compounds (OPs) that are used as plasticizers and flame retardants were analysed in duplicate samples of indoor air from 17 domestic and occupational environments. Solid-phase extraction (SPE) columns were used as adsorbents and analysis was performed using GC with a nitrogen phosphorus selective detector. The total amounts of OPs in the air samples ranged between 36 and 950 ng m(-3); tris(chloropropyl) phosphate (TCPP) and tris(2-chloroethyl) phosphate (TCEP) being the most abundant (0.4 to 730 ng m(-3)), followed by tributyl phosphate (0.5-120 ng m(-3)). Public buildings tended to have about 3-4 times higher levels of OPs than domestic buildings. The relative amounts of individual OPs varied between the sites and generally reflected the building materials, furniture and consumer products used in the sampled environments. Potential sources of these compounds include, inter alia, acoustic ceilings, upholstered furniture, wall coverings, floor polish and polyvinylchloride floor coverings. A correlation was observed between the TCEP concentrations in the air in the sampled environments and previously reported concentrations in dust, but no such correlation was seen for the heavier and less volatile tris(2-butoxyethyl) phosphate (TBEP). Based on estimated amounts of indoor air inhaled and dust ingested, adults and children in the sampled environments would be exposed to up to 5.8 microg kg(-1) day(-1) and 57 microg kg(-1) day(-1) total OPs, respectively.

Direct stereoselective assay of fluoxetine and norfluoxetine enantiomers in human plasma or serum by two-dimensional gas–liquid chromatography with nitrogen–phosphorus selective detection

A method was developed and validated for the direct enantioselective assay of fluoxetine and norfluoxetine in human plasma or serum by two-dimensional capillary gas–liquid chromatography (GC). A Rtx-1 fused-silica capillary (15 m×0.25 mm I.D., 1.0 μm film thickness) and a hydrodex-β-6-TBDM fused-silica capillary (25 m×0.25 mm I.D., 0.25 μm film thickness) were used. A three-step liquid–liquid extraction was used for sample preparation with fluvoxamine and nisoxetine as internal standards. The method provided linear calibration between about 5 and 250 ng/ml for ( R)- and ( S)-fluoxetine as well as 15 and 250 ng/ml for ( R)- and ( S)-norfluoxetine. The limits of detection were about 1.5 and 6 ng/ml, respectively. Intra-day precision (coefficient of variation) was estimated as being between 5.4 and 12.7% at plasma levels of 25, 100 and 200 ng/ml for the four enantiomers. Inter-day precision was between 5.3 and 9.1% at 100 ng/ml. The enantioselective separation of some racemic psychopharmaceuticals was tested with various cyclodextrin GC-capillaries. Advantages and disadvantages of direct enantioselective GC are discussed for the assay of racemic psychopharmaceuticals. Samples from a patient who was treated with racemic fluoxetine were measured. In agreement with literature, plasma levels of the ( R)-enantiomers of fluoxetine and norfluoxetine were considerably decreased in comparison to the ( S)-enantiomers.

Environmental distribution of acetochlor, atrazine, chlorpyrifos, and propisochlor under field conditions.

The environmental behavior, movement, distribution, persistence, and runoff by rainfall of the pesticides acetochlor, atrazine, chlorpyrifos, and propisochlor were studied under field conditions during a five-month period at normal weather conditions. The pesticide concentrations in soil depths of 0-5 and 5-20 cm, and in sediment and runoff water samples (collected from an artificial reservoir built in the lower part of the experimental plot) were measured every second week and following every runoff event. The contamination of a stream running across the lowest part of the plot was also monitored. The weather conditions were also recorded at the experimental site. The pesticide residues were quantified by a capillary gas chromatograph equipped with a nitrogen phosphorus selective detector (GC-NPD). There was a consistent decrease in pesticide residues in the 0-5 cm soil layer with time after spaying. At 140 days after treatment only atrazine and chlorpyrifos were present; acetochlor and propisochlor were not detected in this soil layer. Atrazine and chlorpyrifos in the soil at a depth of 5-20 cm were detectable during the whole experimental interval, whereas acetochlor and propisochlor concentrations were below the limit of detection. Pesticide losses by the surface runoff process and the contamination of the stream were closely related to the time of rainfall elapsed after treatment and amount of rain at the experimental plots. Losses were primarily dependent on surface rainfall volume and intensity. The maximum detected residues of atrazine and acetochlor in stream water were 1 order of magnitude higher than the maximum residue limit specified by the European Union (EU) for environmental and drinking water (0.1 microg/L for individual compounds and 0.5 microg/L for total pesticides). Chlorpyrifos and propisochlor were not detected in this matrix.

Solid-phase microextraction for the assay of levomepromazine in human plasma.

Solid-phase microextraction (SPME) was investigated as sample preparation for the assay of the neuroleptic drug levomepromazine in human plasma. A mixture of human plasma, water, chloramitriptyline as internal standard, and aqueous NaOH was extracted with a 100-microm polydimethylsiloxane (PDMS) fiber (Supelco). The desorption of the fiber was performed in the injection port of a gas chromatograph at 260 degrees C [HP 5890; BPX-5 (SGE): 30 m x 0.53 mm ID, 1-microm film capillary; nitrogen-phosphorus selective detection]. As repeatedly found for SPME analysis of drugs in plasma, the recovery was low (i.e., 7% for levomepromazine). However, the analyte and internal standard were well separated and the calibration was linear from 5 to 180 ng/mL. The within-day precision was 2%, 4%, and 19% at concentrations of 160 ng/mL, 80 ng/mL, and 5 ng/mL, respectively. The between-day precision was 3%, 7%, and 19%, respectively. The limit of determination was 5 ng/mL. The comparison with an established liquid-liquid extraction gas-liquid chromatography method revealed good agreement for spiked samples and patient samples. No interfering peaks of drugs coadministered with levomepromazine or of endogenous substances were found. It is concluded that the method can be used in the therapeutic drug monitoring and clinical toxicology of levomepromazine.

Determination of 4-hydroxyifosfamide concomitantly with ifosfamide and its dechloroethylated metabolites using gas chromatography and a nitrogen phosphorus-selective detector

A sensitive gas chromatographic (GC)/nitrogen phosphorus detection (NPD) system was developed for the determination of the antitumor drug ifosfamide (Ifos) and its 2-dechloroethylifosfamide (2-Difos), 3-dechloroethylifosfamide (3-Difos) and 4-hydroxyifosfamide (4-OHIfos) metabolites in human blood. 4-OHIfos was analyzed after coupling with a trapping agent and was used as an indicator of isophosphoramide mustard (IPM). Ifos and its metabolites 2-DIfos, 3-DIfos, 4-OHIfos and the internal standard (trofosfamide) were extracted into chloroform and then resolved by gas chromatography using a Hewlett Packard HP5 capillary column cross-linked with 5% phenyl methyl silicone (30 m; 530 μm I.D.; 2.65 μm film thickness). Precision and accuracy of the assay were determined over a three-day period and a concentration range of 3.25–50 μg/ml for Ifos, 0.8–14 μg/ml for 2D-Ifos, 0.6–10 μg/ml for 3D-Ifos and 0.08–1.40 μg/ml for 4-OHIfos. The limit of quantitation was set at 3.25, 0.80, 0.62 and 0.08 μg/ml, respectively, for Ifos, 2-DIfos, 3-DIfos and 4-OHIfos.The intra- and inter-day coefficients of variation and accuracies were less than 20%, except for a low concentration 4-OHIfos. This assay was then used to provide pharmacokinetic data on antitumor and toxicologic effects following intravenous infusion of Ifos.

Sample Clean-Up and Fractionation of Organophosphorus Pesticide Residues in Mussels Using Normal-Phase LC

A method has been developed for the sample clean-up of organophosphorus pesticides (OPPs) in mussels prior to gas chromatography analysis. The system applied uses a HPLC pump and a silicagel column A diode array detector is used to monitor, on line, the elution of the fat present in the mussel soft tissue that was extracted with acetonitrile:acetone and redissolved in hexane. Polar and moderately polar pesticides were fractionated and separated from fats using hexane:ethyl acetate 95/5, v/v as mobile phase. The most polar pesticides (chlorfenvinphos, phosmet and dimethoate) were eluted from the column using ethyl acetate. For the elution of non polar pesticides (chlorpyrifos, phorate and fonofos) in fat free fractions it was necessary to use hexane as mobile phase switching on to hexane:ethyl acetate 99/1 (v/v) (4 ml) after 4 min of elution. Quantitative measurement of fat content in collected fractions from LC system was carried out by colorimetry in order to know the efficiency of the clean-up and the amount of fat injected in the GC system. Fat free fractions containing pesticides obtained after LC clean-up can be injected directly, without further clean-up steps or solvent exchange, in the GC system. The limits of detection for the organophosphorus pesticides investigated varied between 1 and 40 ng/g using mass selective detector and between 0.1 and 2 ng/g using nitrogen-phosphorus selective detector. Recoveries of the overall procedure, including extraction and clean-up, were obtained at 400 and 40 ng/g levels and they varied between 89 ± 9% and 105 ± 4%.

Solid-phase microextraction with capillary gas-liquid chromatography and nitrogen-phosphorus selective detection for the assay of antidepressant drugs in human plasma

Solid-phase microextraction (SPME) was tested as a sample preparation for the simultaneous assay of ten antidepressant drugs and metabolites (TADs) in human plasma. Aqueous NaOH (0.5 ml, 1 M) and chloramitriptyline (50 μl, 40 μg/ml) as internal standard (I.S.) were added to a 2-ml plasma sample. This mixture was extracted with a 100-μm polydimethylsiloxane SPME fiber (Supelco) for 10 min. After washing in water and methanol (50%) and subsequent drying at room temperature, desorption of the fiber was performed in the injection port of a gas chromatograph at 260°C for 1 min (HP 5890, DB-17 30 m×0.25 mm I.D., 0.25 μm capillary; 0.7 ml/min nitrogen; nitrogen-phosphorus selective detection). The recovery was found to be very low from plasma (0.3% to 0.8%) but considerably higher from water (about 15%). Therefore, the high protein binding of antidepressants appears to be the main limiting mechanism for a better extraction. However, the analytes were well separated and the calibrations were linear between 125 ng/ml and 2000 ng/ml. The limits of quantification were about 90 ng/ml for imipramine and desipramine, 125 ng/ml for amitriptyline, trimipramine, doxepine, nortriptyline and mianserine and about 200 ng/ml for maprotiline, clomipramine and desmethylclomipramine. The recovery was improved by increasing the extraction time. The influence of the concentrations of the sum of proteins and of α-acid glycoprotein on the peak-area ratios A TAD/ A I.S. and on absolute peak areas was studied. Peak-area ratios increased with decreasing protein concentration but were found to be independent on α-acid glycoprotein. A simple model for the explanation of the effect is presented. Measures for the improvement of sensitivity are discussed. As presented in this paper, which first describes SPME for the analysis of drugs in plasma, SPME with a short extraction time can be of only very limited value for therapeutic drug monitoring. Lower concentrations than the limit of quantification are usually found at therapeutic doses. The method can be useful for toxicological analysis after the accidental or suicidal intake of higher doses. However, an about 10-fold improvement of the sensitivity of the method seems to be possible.

Determination of amino acids in biological fluids by capillary gas chromatography with nitrogen-phosphorus selective detection

A selective and sensitive method for the determination of protein and non-protein amino acids in biological fluids by capillary gas chromatography (GC) has been developed. The amino acids in the samples were directly converted into their N( O, S)-isobutoxycarbonyl methyl ester derivatives and measured by GC with nitrogen-phosphorus selective detection (NPD) using a DB-17ht capillary column. Using this method, the derivatives of the 21 protein amino acids and the 25 non-protein amino acids provided excellent NPD responses and were quantitatively and reproducibly resolved within 28 min. The lower detection limits of these amino acids, at a signal-to-noise ratio of 3, were ca. 6–150 pg injected. The calibration curves for each amino acid in the range of 0.02–2 μg were linear and sufficiently reproducible for quantitative analysis. This method was successfully applied to small urine and serum samples without prior clean-up; there was no evidence of interference from coexisting substances. Overall recoveries of amino acids added to urine and serum samples were 83–112%. The intra-assay and inter-assay R.S.D. of amino acids in these samples were 0.3–8.9% ( n = 3) and 1.9–15.8% ( n = 3) respectively.

Selective and Sensitive Determination of Protein and Non‐Protein Amino Acids by Capillary Gas Chromatography with Nitrogen–Phosphorus Selective Detection

Selective and Sensitive Determination of Protein and Non‐Protein Amino Acids by Capillary Gas Chromatography with Nitrogen–Phosphorus Selective Detection

Analysis of heterocyclic amines as their N-dimethylaminomethylene derivatives by gas chromatography with nitrogen-phosphorus selective detection

A selective and sensitive method was developed for the determination of heterocyclic amines (HCAs) by gas chromatography (GC). HCAs were converted into their N-dimethylaminomethylene derivatives and measured by GC with nitrogen-phosphorus selective detection using two connected fused-silica capillary columns containing DB-1 and DB-17ht. The derivatives of the 10 HCAs were sufficiently volatile and stable to give single symmetrical peaks. The calibration curves for HCAs in the range 0.5–10 ng were linear with correlation coefficients being above 0.998. The detection limits at a signal-to-noise ratio of 3 were ca. 2–15 pg per injection.

O-3-5 - The depression-anxiety syndrome in dementia

Solid-phase microextraction (SPME) was tested as a sample preparation for the simultaneous assay of ten antidepressant drugs and metabolites (TADs) in human plasma. Aqueous NaOH (0.5 ml, 1 M) and chloramitriptyline (50 μl, 40 μg/ml) as internal standard (I.S.) were added to a 2-ml plasma sample. This mixture was extracted with a 100-μm polydimethylsiloxane SPME fiber (Supelco) for 10 min. After washing in water and methanol (50%) and subsequent drying at room temperature, desorption of the fiber was performed in the injection port of a gas chromatograph at 260°C for 1 min (HP 5890, DB-17 30 m×0.25 mm I.D., 0.25 μm capillary; 0.7 ml/min nitrogen; nitrogen-phosphorus selective detection). The recovery was found to be very low from plasma (0.3% to 0.8%) but considerably higher from water (about 15%). Therefore, the high protein binding of antidepressants appears to be the main limiting mechanism for a better extraction. However, the analytes were well separated and the calibrations were linear between 125 ng/ml and 2000 ng/ml. The limits of quantification were about 90 ng/ml for imipramine and desipramine, 125 ng/ml for amitriptyline, trimipramine, doxepine, nortriptyline and mianserine and about 200 ng/ml for maprotiline, clomipramine and desmethylclomipramine. The recovery was improved by increasing the extraction time. The influence of the concentrations of the sum of proteins and of α-acid glycoprotein on the peak-area ratios ATAD/AI.S. and on absolute peak areas was studied. Peak-area ratios increased with decreasing protein concentration but were found to be independent on α-acid glycoprotein. A simple model for the explanation of the effect is presented. Measures for the improvement of sensitivity are discussed. As presented in this paper, which first describes SPME for the analysis of drugs in plasma, SPME with a short extraction time can be of only very limited value for therapeutic drug monitoring. Lower concentrations than the limit of quantification are usually found at therapeutic doses. The method can be useful for toxicological analysis after the accidental or suicidal intake of higher doses. However, an about 10-fold improvement of the sensitivity of the method seems to be possible.

Disks versus columns in the solid-phase extraction of pesticides from water

Forty four pesticides including organochlorine, organophosphorus, carbamate, triazine and other pesticide structures were extracted from distilled water spiked at 0.4 μg l −1 level using octyl- (C 8) and octadecyl-silica (C 18) based supports which are fixed on a PTFE membrane disk or hand-packed in glass minicolumns. Determination was carried out by capillary gas chromatography with an electron capture detector and a nitrogen-phosphorus selective detector operating in parallel. The analytical behaviour of C 8 and C 18 Empore membrane disks and C 8 and C 18 preparative Bondapak in glass minicolumns was studied on the basis of the statistical differences. On the whole, the minicolumns provided better recoveries than the disks, whereas with the same kind of support (disk or column), the results obtained with C 8 were close to those obtained with C 18, except for carbamate and triazine pesticides in which the C 8 disks provided better recoveries than the C 18 ones. The theoretical and practical differences between the disks and columns were also examined.

Development of a gas chromatographic method for the simultaneous determination of trace amounts of ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid in natural waters

A GC method for the simultaneous determination of ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) in natural waters is described. The method was studied with spiked samples of distilled water, sea-water (2 matrices) and humic-containing lake water. An acidified 5–10 ml sample was evaporated and esterified with C2H5OH, containing H2SO4 and CH3COOH catalysts and CH3(CH2)15CN as an internal standard. The esterified sample was extracted with C6H5CH3, neutralized with KHCO3, dried with anhydrous Na2SO4 and analysed by GC with nitrogen–phosphorus selective detection. The best recoveries were obtained by the esterification in 100 °C for 3 h. The tetraethyl ester of EDTA and pentaethyl ester of DTPA were further identified by mass spectrometry. In the sea- and lake water matrices, the recoveries of EDTA and DTPA were 80–110%. High concentrations (above 50 mg l–1) of iron (Fe3+) interfered considerably in the determination of DTPA. For EDTA the interference was insignificant with iron concentrations below 500 mg l–1.

Rising-dose fluvoxamine therapy in depression; an overview of two clinical studies

Solid-phase microextraction (SPME) was tested as a sample preparation for the simultaneous assay of ten antidepressant drugs and metabolites (TADs) in human plasma. Aqueous NaOH (0.5 ml, 1 M) and chloramitriptyline (50 μl, 40 μg/ml) as internal standard (I.S.) were added to a 2-ml plasma sample. This mixture was extracted with a 100-μm polydimethylsiloxane SPME fiber (Supelco) for 10 min. After washing in water and methanol (50%) and subsequent drying at room temperature, desorption of the fiber was performed in the injection port of a gas chromatograph at 260°C for 1 min (HP 5890, DB-17 30 m×0.25 mm I.D., 0.25 μm capillary; 0.7 ml/min nitrogen; nitrogen-phosphorus selective detection). The recovery was found to be very low from plasma (0.3% to 0.8%) but considerably higher from water (about 15%). Therefore, the high protein binding of antidepressants appears to be the main limiting mechanism for a better extraction. However, the analytes were well separated and the calibrations were linear between 125 ng/ml and 2000 ng/ml. The limits of quantification were about 90 ng/ml for imipramine and desipramine, 125 ng/ml for amitriptyline, trimipramine, doxepine, nortriptyline and mianserine and about 200 ng/ml for maprotiline, clomipramine and desmethylclomipramine. The recovery was improved by increasing the extraction time. The influence of the concentrations of the sum of proteins and of α-acid glycoprotein on the peak-area ratios ATAD/AI.S. and on absolute peak areas was studied. Peak-area ratios increased with decreasing protein concentration but were found to be independent on α-acid glycoprotein. A simple model for the explanation of the effect is presented. Measures for the improvement of sensitivity are discussed. As presented in this paper, which first describes SPME for the analysis of drugs in plasma, SPME with a short extraction time can be of only very limited value for therapeutic drug monitoring. Lower concentrations than the limit of quantification are usually found at therapeutic doses. The method can be useful for toxicological analysis after the accidental or suicidal intake of higher doses. However, an about 10-fold improvement of the sensitivity of the method seems to be possible.

Nanogram level quantitation of oxycodone in human plasma by capillary gas chromatography using nitrogen—phosphorus selective detection

A sensitive and specific capillary gas chromatographic assay is reported for the quantitation of oxycodone in human plasma. The technique involves a single extraction of oxycodone and internal standard (hydrocodone) from plasma by toluene containing 1% isopropanol. Separation is achieved on a methyl silicone (HP-1) fused-silica capillary column (25 m × 0.2 mm I.D., 0.33 μm film thickness) and detection is by nitrogen—phosphorus selective mode. The minimum quantifiable limit is 1.8 ng/ml using 2 ml of plasma. The method is applicable to characterize the plasma profile of oxycodone in humans after a single oral 5-mg oxycodone hydrochloride tablet.

Determination of volatile amines in sediment and water samples

A sensitive and reproducible method was developed for the determination of μg l −1 levels of methylamines in marine samples. The compounds are preconcentrated from water or pore-water samples by microdiffusion, then determined by gas chromatography on a packed column of untreated Chromosorb 103 (60–80 mesh), using a nitrogen—phosphorus-selective detector.

Solid-phase extraction for multi-residue analysis of some triazole and pyrimidine pesticides in water

A multi-residue analytical method based on solid-phase extraction (C18) has been developed for the analysis of 12 compounds in groundwater. These compounds are triazoles, e.g. diclobutrazol, flutriafol, hexaconazole, paclobutrazol and its ketone analogue and pyrimidines, e.g. bupirimate, pirimicarb, pirimiphos-methyl, ethirimol, and other pesticides: fluazifop-P-butyl, fluazifop and fomesafen. In summary, one litre of water modified with 1% methanol was extracted using a C18 solid-phase extraction column, containing 1 g of adsorbent. The retained compounds were eluted from the column with successive elutions of acetonitrile and methanol. No further clean-up was necessary. Residues were determined either by capillary gas-liquid chromatography (GLC) using a nitrogen-phosphorus selective detector, or high performance liquid chromatography (HPLC) using a UV detector. Recovery data on these compounds were obtained by fortifying water at 0.05–100 μg/l levels. Depending on the compound, mean recoveries were within the range of 80–107% with a coefficient of variation of 9–15%. The limit of determination, defined as four times the baseline noise, varied between 0.003–0.1 μg/l also depending on the compound and detection sensitivity of the instrument. These recovery data have also been compared to values generated by conventional liquid-liquid partition. Various techniques were used to confirm the identity of these compounds. Gas Chromatography-Mass Spectrometry (GC-MS) using selective ion monitoring (SIM) was used to confirm the compounds which were amenable to gas-liquid chromatography. These were all the triazoles and bupirimate, pirimicarb, pirimiphos-methyl and fluazifop-P-butyl. HPLC methods were developed using different mobile phase and adsorbent combinations for the confirmation of ethirimol, fluazifop and fomesafen residues in water.

Two Cases of Fatal Intoxication due to Tranylcypromine Overdose

Two cases of death following the ingestion of tranylcypromine are presented. High concentrations of tranylcypromine were determined in blood, urine, and liver by gas-liquid chromatography. Tranylcypromine was extracted from buffered blood with n-butyl chloride. The evaporated extract was derivatized with trifluoroacetic anhydride and analyzed by gas chromatography with nitrogen-phosphorus selective detection. The method was linear in blood over the range 0.5-20 mg/L with a limit of quantitation of about 0.2 mg/L.