首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
This paper reports on an absorption method used for the determination of six target volatile methylsiloxanes and trimethylsilanol existing in raw biogas samples by means of a special and portable sampling train system. After biogas sampling (no accurate pump needed), the samples obtained were analysed by gas chromatography-mass spectrometry (GC-MS). The optimisation of the used solvent was carried out, and acetone was selected as the preferred liquid medium for trapping the siloxanes. The results clearly showed that using pure acetone and a mixture of acetone and water (97/3% = v/v) ensures very good solvation of silicon-contained molecules; thus the sampling procedure was more accurate. Replicate samples showed that the relative standard deviation of the method was less than 5.7% and 6.3% for methylsiloxanes as well as less than 2.1% and 2.4% for trimethylsilanol analysed 24 and 72 hours after sampling, respectively. Furthermore, limits of detection were determined theoretically and experimentally. The limits of detection for siloxanes and trimethylsilanol were in the range 0.04–0.11 mg/Nm3 and 0.08–0.12 mg/Nm3, respectively. The limit of quantification for trimethylsilanol was 0.1 mg/Nm3, whereas the limit for siloxanes ranged from 0.1 to 0.13 mg/Nm3. Finally, raw biogas samples were successfully analysed by the developed method. Trimethylsilanol and methylsiloxanes were found in the concentrations of 34.5 mg/Nm3 and 1.7–20 mg/Nm3 in the analysed raw biogas, respectively.  相似文献   

2.
An analytical method based on TD-GC/MS was developed and validated for the determination of volatile organic compounds (VOCs), including linear and cyclic volatile methylsiloxanes (VMSs), in biogas. Biogas was first sampled in Supel? Inert Film bags and subsequently dynamically sampled onto multisorbent bed tubes (Carbotrap, Carbopack X and Carboxen 569) using portable pump equipment. Two sample volumes, 100 and 250 ml, were evaluated. Desorption efficiency values for both volumes are in the range of 99–100% for almost all studied compounds while breakthrough values (%VOC on sample tube back section) are below 1% for most evaluated VOCs. However, acetaldehyde, carbon disulphide, ethanol and 1,3-butadiene have breakthrough values higher than 5%. Method detection limits were in the range of 0.01–0.8 ng per sample. The most abundant VOCs in biogas were terpenes with concentrations between 500 and 700 mg m?3. Other important families were ketones, aromatic hydrocarbons and alkanes, with concentrations in the range of 36–46 , 20–35 and 14–16 mg m?3, respectively. VMSs presented average concentrations of 4.9 ± 0.4 mg m?3. Additionally, the Supel? Inert Film bags were evaluated for stability for 4 days at room temperature. Although several VOC families’ concentrations in the bag increased or decreased significantly (t-test; p ≤ 0.01, = 5) 2 days after collection, recoveries were around 70–130% for most studied VOCs. The results shown demonstrate that the presented methodology is reliable and satisfactory for the evaluation of VOCs in biogas and presents an alternative to the currently existing biogas analytical techniques.  相似文献   

3.
《Analytical letters》2012,45(17):2747-2757
Abstract

Brazilian sugarcane spirits were analyzed to elucidate similarities and dissimilarities by principal component analysis. Nine aldehydes, six alcohols, and six metal cations were identified and quantified. Isobutanol (LD 202.9 µg L?1), butiraldehyde (0.08–0.5 µg L?1), ethanol (39–47% v/v), and copper (371–6068 µg L?1) showed marked similarities, but the concentration levels of n-butanol (1.6–7.3 µg L?1), sec-butanol (LD 89 µg L?1), formaldehyde (0.1–0.74 µg L?1), valeraldehyde (0.04–0.31 µg L?1), iron (8.6–139.1 µg L?1), and magnesium (LD 1149 µg L?1) exhibited differences from samples.  相似文献   

4.
The possibility of using ionic liquid based chitosan sorbent for the separation and preconcentration of fluoroquinolone antibiotics (marbofloxacin, enoxacin, ofloxacin, ciprofloxacin, and enrofloxacin) has been studied. For this reason, different ionic liquids were prepared and coated on the chitosan sorbent. The conditions of the preconcentration of fluoroquinolones on a microcolumn have been optimized and the extraction efficiencies of the prepared sorbents have been compared. The compounds were eluted with 5 mL of 20% NH3 (v/v, MeOH) solution and determined by HPLC with diode array and fluorescence detector. The limits of detection were found as 4.23 µ g L?1 for marbofloxacin, and 1.09 µg L?1 for enoxacin; 3.23 × 10?3 µg L?1 for ofloxacin; 8.39 × 10?3 µg L?1 for ciprofloxacin; and 19.50 × 10?3 µg L?1 for enrofloxacin. The developed method was applied for the analysis of fluoroquinolone in milk, egg, fish, bovine, and chicken samples and the recoveries were obtained in the range 70–100%.  相似文献   

5.
M. Ajhar  B. Wens 《Talanta》2010,82(1):92-9278
Landfill or digester gas can contain man-made volatile methylsiloxanes (VMS), usually in the range of a few milligrams per normal cubic metre (Nm3). Until now, no standard method for siloxane quantification exists and there is controversy with respect to which sampling procedure is most suitable. This paper presents an analytical and a sampling procedure for the quantification of common VMS in biogas via GC-MS and polyvinyl fluoride (Tedlar®) bags. Two commercially available Tedlar bag models are studied. One is equipped with a polypropylene valve with integrated septum, the other with a dual port fitting made from stainless steel. Siloxane recovery in landfill gas samples is investigated as a function of storage time, temperature, surface-to-volume ratio and background gas. Recovery was found to depend on the type of fitting employed. The siloxanes sampled in the bag with the polypropylene valve show high and stable recovery, even after more than 30 days. Sufficiently low detection limits below 10 μg Nm−3 and good reproducibility can be achieved. The method is therefore well applicable to biogas, greatly facilitating sampling in comparison with other common techniques involving siloxane enrichment using sorption media.  相似文献   

6.
《Analytical letters》2012,45(14):2214-2231
Abstract

A new simple and sensitive method has been proposed for rapid determination of trace levels of silver in environmental water samples, using dispersive liquid–liquid microextraction (DLLME) prior to its microsample introduction-flame atomic absorption spectrometry. Under the optimum conditions, the linear range was 0.1–7 µg L?1 and limit of detection was 0.018 µg L?1. The relative standard deviation for 0.50 and 5.00 µg L?1 of silver in water sample was 4.0 and 1.7%, respectively. The relative recoveries of silver from tap, well, river, and seawater samples at spiking levels of 1.00 and 5.00 µg L?1 were in the range of 86.4–98.6%.  相似文献   

7.
《Analytical letters》2012,45(5):932-941
The heavy metal content was investigated for six mushroom species native to Jordan. Metal (Cu, Pb, Cd, Fe, Zn, Mn, Ni, and Co) content in soil substrate and their relation to metal concentrations in mushroom and underlying soil were determined by flame and graphite furnace atomic absorption spectrometry. Mushroom species and soil were collected from different places in Jordan. The highest Cu level was 51.84 µg g?1 for the species Lepista nuda; whereas, the lowest Cu level was found to be 18.51 µg g?1 in Calvatia utriformis. Among the wild mushrooms, the highest Pb level was found as 4.81 µg g?1 in Bovista plumbea, whereas the lowest Pb concentration was 2.01 µg g?1 in Calvatia utriformis. The highest Cd level was determined as 1.9 µg g?1 for Lepista nuda, whereas the lowest Cd level was 0.58 µg g?1 for the species of Polyporus frondosus. The highest Zn level was 58.77 µg g?1 for the species of Lepista nuda and the lowest Zn concentration was found 35.98 µg g?1 in Calvatia utriformis. The highest Fe level was found as 317 µg g?1 in Lepista nuda, whereas the lowest Fe concentration was 211.7 µg g?1 in Calvatia utriformis. The highest Mn content was 36.55 µg g?1 for Russula delica, whereas the lowest Mn level was 24.5 µg g?1 for the species Bovista plumbea. The highest Ni content was found as 12.65 µg g?1 for Russula delica, whereas the lowest Ni level was 0.17 µg g?1 for Bovista plumbea. The highest Co content in the tested mushrooms was found as 3.5 µg g?1 for the species of Agaricus bisporus, whereas the lowest Co level was 0.85 µg g?1 for Polyporus frondosus. The results indicated that, in general, heavy metal contents in all mushroom species were lower than the underlying soil substrates except for some mushroom species.  相似文献   

8.
《Analytical letters》2012,45(2):356-366
A fast, simple and sensitive method for determining of lead in hair dyes using graphite furnace atomic absorption spectrometry with slurry sampling was developed. Multivariate optimization was used to establish optimal analytical parameters through a fractional factorial and a central composite design. The samples were submitted for direct analysis without prior digestion and were diluted in 2.5% v/v HNO3 and 1.5% v/v H2O2. Palladium (chemical modifier) and rhodium (permanent modifier) were selected from several potential modifiers. The optimal conditions were a pyrolysis time of 10 s (liquid and dust dyes) 20 s (cream dyes), a pyrolysis temperature of 789°C (liquid dyes) or 750°C (cream and dust dyes) and an atomization temperature of 1800°C for all dyes. Under optimum conditions, the calibration graph is linear in the 1.50–50.0 µg L?1 concentration range, with a detection limit of 0.33, 0.44, and 0.39 µg L?1 for liquid, dust, and cream hair dyes, respectively. The relative standard deviation ranged from 1.63 to 4.56%. The recovery rate ranged from 85 to 108%, and no significant differences were found between the results obtained with the proposed method and the microwave decomposition analysis method of real samples. The concentration ranges obtained for lead in the hair dyes samples were 1.00–11.3 µg L?1 for liquid dyes, 14.0–100 µg kg?1 for dust dyes, and 19.9–187 µg kg?1 for cream dyes.  相似文献   

9.
《Analytical letters》2012,45(4):570-581
Two simple, sensitive, and specific high-performance liquid chromatography and thin-layer chromatography methods were developed for the simultaneous estimation of Amlodipine besilate (AM) and Valsartan (VL). Separation by HPLC was achieved using a xTerra C18 column and methanol /acetonitrile /water/ 0.05% triethylamine in a ratio 40:20:30:10 by volume as mobile phase, pH was adjusted to 3 ± 0.1 with o-phosphoric acid. The flow rate was 1.2 mL min?1. The linearity range was 0.2 to 2 µg mL?1 for amlodipine besilate and 0.4 to 4 µg mL?1 for Valsartan with a mean percentage recovery of 99.59 ± 0.523% and 100.61 ± 0.400% for amlodipine besilate and valsartan, respectively. The TLC method used silica gel 60 F254 plates; the optimized mobile phase was ethyl acetate/ methanol / ammonium hydroxide (55:45:5 by volume). Quantitatively, the spots were scanned densitometrically at 237 nm. The range was 0.5–4.0 µg spot?1 for amlodipine besilate and 2.0–12.0 µg spot?1 for valsartan. The mean percentages recovery was 99.80 ± 0.451% and 100.61 ± 0.363% for amlodipine besilate and valsartan, respectively. The HPLC method was found to be simple, selective, precise, and reproducible for the estimation of both drugs from spiked human plasma.  相似文献   

10.
《Analytical letters》2012,45(11):1952-1964
The distributions of cadmium and lead in marine sediments, surrounding soil, stones, and atmospheric particulate matter were determined at different locations in Split, Croatia. The determination of cadmium and lead was performed by flame atomic absorption spectrometry whereas atmospheric particulate matter samples were analyzed by inductively coupled plasma–optical emission spectrometry. Cadmium concentrations in the stones and soil were between 0.2 to 0.6 µg g?1 and 0.2 to 0.9 µg g?1. The concentration in the atmospheric particulate matter were <0.2 µg m?2 d?1(detection limit) to 1.4 µg m?2 d?1. Lead concentrations in marine sediments, stones, soil, and atmospheric particulate matter ranged from 31.2 to 144.4 µg g?1, 9.3 to 29.4 µg g?1, 11.3 to 66.1 µg g?1, and 0.5 to 241.4 µg m?2 d?1, respectively. The relationship between determined parameters was established using principal component analysis and the results are in agreement with the assumption that anthropogenic sources play important roles for lead and cadmium distribution.  相似文献   

11.
A sensitive and high selective chemiluminescence (CL) method was developed for the determination of lincomycin in acid medium using diperiodatonickelate as a reagent. The mechanism leading to luminescence is discussed by comparing the spectra of fluorescence and CL. Relative CL intensity is linear in the range from 8.0 ng mL?1 to 1.0 µg mL?1, the limit of detection is 2.5 ng mL?1 (3σ), and the relative standard deviation is 4.0% at 0.1 µg mL?1 of lincomycin (n?=?7). The method was successfully applied to the determination of lincomycin in injections, human urine, and in serum samples.  相似文献   

12.
《Analytical letters》2012,45(10):1634-1649
A selective method for the determination of fourteen nitroimidazoles and their hydroxy-metabolites in honey was developed based on improved molecularly imprinted solid-phase extraction followed by liquid chromatography–tandem mass spectrometry. The separation of analytes was performed on a C18 column using a mobile phase of 0.1% formic acid in acetonitrile and 0.1% formic acid in water with gradient elution. The method was suitable for metronidazole, hydroxymetronidazole, dimetridazole, ronidazole, hydroxydimetridazole, ipronidazole, hydroxyipronidazole, carnidazole, menidazole, nimorazole, ornidazole, secnidazole, ternidazole, and tinidazole. The procedure was evaluated according to EU Commission Decision 2002/657/EC requirements by determining linearity, specificity, recovery, repeatability, within-laboratory reproducibility, decision limit, detection capability, matrix effects, and stability. The method determined nitroimidazoles and their hydroxy-metabolites below the recommended concentration level of 3 µg kg?1. The decision limits and detection capabilities ranged from 0.110 µg kg?1 to 0.387 µg kg?1 and from 0.179 µg kg?1 to 0.508 µg kg?1, respectively. The results from stability tests indicated that all analyzed nitroimidazoles were stable in honey stored at 4°C for at least 28 weeks and that elevated temperature and exposure to light exposure accelerated their degradation. The method was successfully applied to the analysis of a wide variety of honey samples.  相似文献   

13.
A stability-indicating ultra-high-performance liquid chromatography (UHPLC) method with a diode array detector was developed and validated for the determination of cis/trans isomers of perindopril l-arginine in bulk substance and pharmaceutical dosage form. The separation was achieved on a Poroshell 120 Hilic (4.6 × 150 mm, 2.7 µm) column using a mobile phase composed of acetonitrile–0.1 % formic acid (20:80 v/v) at a flow rate of 1 mL min?1. The injection volume was 5.0 µL and the wavelength of detection was controlled at 230 nm. The selectivity of the UHPLC-DAD method was confirmed by determining perindopril l-arginine in the presence of degradation products formed during acid–base hydrolysis and oxidation as well as degradation in the solid state, at an increased relative air humidity and in dry air. The method’s linearity was investigated in the ranges 0.40–1.40 µg mL?1 for isomer I and 0.40–2.40 µg mL?1 for isomer II of perindopril l-arginine. The UHPLC-DAD method met the precision and accuracy criteria for the determination of the isomers of perindopril l-arginine. The limits of detection and quantitation were 0.1503 and 0.4555 µg mL?1 for isomer I and 0.0356 and 0.1078 µg mL?1 for isomer II, respectively.  相似文献   

14.
This study deals with the utilization of chicken feather waste as a substrate for anaerobic digestion and improving biogas production by degradation of the compact structure of the feather keratin. In order to increase the digestibility of the feather, different pretreatments were investigated, including thermal pretreatment at 120 °C for 10 min, enzymatic hydrolysis with an alkaline endopeptidase [0.53–2.66 mL/g volatile solids (VS) feathers] for 0, 2, or 24 h at 55 °C, as well as a combination of these pretreatments. The effects of the treatments were then evaluated by anaerobic batch digestion assays at 55 °C. The enzymatic pretreatment increased the methane yield to 0.40 Nm3/kg VSadded, which is 122 % improvement compared to the yield of the untreated feathers. The other treatment conditions were less effective, increasing the methane yield by 11–50 %. The long-term effects of anaerobic digestion of feathers were examined by co-digestion of the feather with organic fraction of municipal solid waste performed with and without the addition of enzyme. When enzyme was added together with the feed, CH4 yield of 0.485 Nm3/kg VS?1 d?1 was achieved together with a stable reactor performance, while in the control reactor, a decrease in methane production, together with accumulation of undegraded feather, was observed.  相似文献   

15.
《Analytical letters》2012,45(5):761-777
This article reviews the use of square wave anodic stripping voltammetry for the simultaneous determination of ecotoxic metals (Pb, Cd, Cu, and Zn) on a bismuth-film (BiFE) electrode. The BiFE was prepared in situ on a glassy-carbon electrode (GCE) from the 0.1 mol L?1 acetate buffer solution (pH 4.5) containing 200 µg L?1 of bismuth (III). The addition of hydrogen peroxide to the electroanalytical cell proved beneficial for the interference-free determination of Cu (II) together with zinc, lead, and cadmium, using the BiFE. The experimental variables were investigated and optimized with the view to apply this type of voltammetric sensor to real samples containing traces of these metals. The performance characteristics, such as reproducibility, decision limit (CCa), detection capability (CCβ), sensitivity, and accuracy indicated that the method holds promise for trace Cu2+, Pb2+, Cd2+, and Zn2+ levels by employment of Hg-free GCE with SWASV. CCa, and CCβ were calculated according to the Commission Decision of 12 August 2002 (2002/657/EC). Linearity was observed in the range 20–280 µg L?1 for zinc, 10–100 µg L?1 for lead, 10–80 µg L?1 for copper, and 5–50 µg L?1 for cadmium. Using the optimized conditions, the stripping performance of the BiFE was characterized by low limits of detection (LOD). Finally, the method was successfully applied in real as well as in certified reference water samples.  相似文献   

16.
In this paper, a novel molecularly imprinted polymer coated stir bar has been used to selectively extract naphthalene sulfonates (NSs) directly from seawater sample. 1-Naphthalene sulfonic acid (1-NS) was used as template molecule. The effects of different parameters were optimized on the extraction efficiency and the optimum conditions were established as: the absorption and desorption times were fixed, respectively, at 10 and 15 min, stirring speed was 700 rpm, pH was adjusted to 4.1, amount of NaCl was 1 mol L?1 and extraction process was performed at a temperature of 50 °C. The linear ranges were 2–250 µg L?1 for 3,6-NDS-1-OH (1-naphthol-3,6-disulfonic acid), 4–250 µg L?1 for 2-NS (2-naphthalene sulfonate) and 3–250 µg L?1 for 1-NS. The detection limits were within the range of 0.32–0.95 µg L?1. Under optimum conditions, the detection limits of the NSs were 0.84, 0.95 and 0.32 µg L?1 with the enrichment factor of 117-, 41- and 77-fold for 2-NS, 1-NS, and 6-NDS-1-OH, respectively. The repeatability of the method was satisfactory (0.53 ≤ RSD ≤6.0 %, n = 10). The method has been successfully applied for the analysis of trace amounts of three naphthalene sulfonates in seawater of Chabahar Bay.  相似文献   

17.
《Analytical letters》2012,45(9):1663-1673
An on-line two-dimension microflow liquid chromatography was developed for better separation and analysis of the highly complex ingredients of medicinal preparation of traditional Chinese medicine Coptis Chinensis Franch. A two-valve switching system was utilized for two-dimension chromatography with strong cation exchange and reverse-phase capillary columns separation. The components were separated well by this system and yielded over 420 peaks. Under the optimal condition, 4 compounds were detected quantitatively. A good linear relationship was obtained from 0.2 µg mL?1 to 24 µg mL?1with detection limits (S/N = 3) ranging from 0.05 µg mL?1 to 0.2 µg mL?1for the compounds. We demonstrated that the method can be successfully applied to the analysis of a natural complex sample, with satisfactory results.  相似文献   

18.
《Analytical letters》2012,45(14):2037-2052
A rapid and simple flow injection (FI) method is reported for the determination of vitamin A (retinol) based on its strong enhancing effect on the Ce(IV)–Na2SO3 chemiluminescence (CL) reaction in an acidic solution. The effect of key chemical and physical parameters (i.e., reagent concentrations, flow rate, and sample volume) was optimized and potential interferences examined. Under the selected experimental conditions, a linear calibration was obtained between the CL intensity and vitamin A concentration in the range 0.1–8.0 µg mL?1 (r 2  = 0.9986, n = 8). The limit of detection (3 s x blank) was 0.01 µg mL?1 retinol (n = 6) and the relative standard deviation (RSD) for 0.25 µg mL?1 retinol was 2.3% (n = 10) with a sampling rate of 180 h?1. The method was successfully applied to infant milk-based formulas and pharmaceutical formulations and the results were not significantly different at 95% confidence interval with those obtained by using a spectrophotometric reference method. The possible CL mechanism is also discussed briefly supporting with UV-visible, fluorescence, and CL spectra.  相似文献   

19.
《Analytical letters》2012,45(14):1995-2005
Using 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6MIM][PF6]) ionic liquid as extraction solvent, five estrogens including estrone (E1), 17β-estradiol (E2), estriol (E3), 17α -ethynylestradiol (EE2), and diethylstilbestrol (DES) in water samples were determined by dispersive liquid-liquid microextraction (DLLME) followed by high performance liquid chromatography with a photodiode array detector and a fluorescence detector (HPLC-DAD-FLD). The extraction procedure was induced by the formation of cloudy solution, which was composed of fine drops of [C6MIM][PF6] dispersed entirely into the sample solution with the help of a disperser solvent (acetone). Parameters including both extraction and disperser solvents and their volumes, extraction and centrifugal time, sample pH, and salt effect were investigated and optimized. Under the optimized conditions, 110–349 fold enrichment factors of analytes were obtained. The calibration curves were linear in the concentration range of 0.2–100 µg L?1 for E2, E3, and EE2 detected with FLD, and 1–100 µg L?1 for E1 and DES detected with DAD. The correlation coefficient of the calibration curve was between 0.9990 and 0.9997. The limits of detection (LOD, S/N = 3) for the five estrogens were in the range of 0.08–0.5 µg L?1. The relative standard deviations (RSD) for six replication experiments at the concentration of 5.0 µg L?1 were ≤5.7%. The proposed method was applied to the analysis of three water samples from different sources (river water, waste water, and sea water). The relative recoveries of spiked water samples are satisfied with 89.3–102.4% and 88.7–105.2% at two different concentration levels of 5.0 and 50.0 µg L?1, respectively.  相似文献   

20.
《Analytical letters》2012,45(10):1759-1771
A robust gold-coated solid-phase microextraction fiber was rapidly prepared on an etched stainless-steel wire based on chemical deposition. Gold(III) was reduced to produce a mechanically robust fiber with a stable coating. Subsequently, it was applied for solid-phase microextraction of five polycyclic aromatic hydrocarbons in water samples coupled to high performance liquid chromatography with an ultraviolet-visible detector. The preconcentration conditions were optimized, including extraction and desorption time, temperature, stirring rate, and ionic strength. Under the optimized conditions, the calibration graphs were linear in the range from 1 to 500 µg · L?1 for naphthalene and 0.20–500 µg · L?1 for phenanthrene, anthracene, fluoranthene, and pyrene. Limits of detection were between 0.016 and 0.22 µg · L?1 (signal-to-noise ratio = 3). The analysis of water samples showed that the recoveries ranged from 86.0% to 112.9% with relative standard deviations between 2.03% and 11.7%. The fiber coating was sensitive and suitable for the preconcentration and determination of polycyclic aromatic hydrocarbons in environmental waters. Compared with previously reported solid-phase microextraction methods, this device offered easy preparation, low cost, resistance to organic solvents, good stability, and high durability.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号