Determination of geosmin and 2-methylisoborneol in water using solid-phase microextraction and gas chromatography-chemical ionisation/electron impact ionisation-ion-trap mass spectrometry

A method for the determination of geosmin and 2-methylisoborneol (MIB) in water by solid-phase microextraction (SPME) is presented. Various SPME fibre chemistries have been compared for their efficiency in extracting MIB from water. Extraction conditions including the extraction time and temperature have been optimised. A 30 ml water sample is extracted for 20 min at 60 degrees C using a divinylbenzene fibre, and the extract analysed by gas chromatography with ion-trap mass spectrometry detection. d5-Geosmin and d3-MIB are added as internal standards to compensate for any variability in the SPME process which is not carried out to equilibrium. Chemical ionisation, using acetonitrile as the reagent gas, was found to give superior sensitivity to electron impact ionisation (EI) for the detection of MIB. EI was used as the ionisation mode for detection of geosmin. The method shows good linearity over the concentration range 5-40 ng l-1 and gives detection limits of 1 ng l-1 for both geosmin and MIB. Recovery (93-110%) and precision (3-12%) over this concentration range, for both raw and treated drinking waters, are comparable to currently employed methods such as closed-loop stripping analysis (CLSA). The method offers the advantage of being simple to use, with much shorter analysis times in comparison to CLSA.     

Interlaboratory study of the Charm ROSA Safe Level Aflatoxin M1 Quantitative lateral flow test for raw bovine milk

An interlaboratory study of 21 public health, state agriculture, and industry laboratories in the United States tested raw commingled bovine milk containing aflatoxin M1 using the Charm Rapid One Step Assay (ROSA) Safe Level Aflatoxin M1 Quantitative lateral flow method. Blind coded sample pairs were fortified with 0, 300, 350, 400, 450, 500, and 550 parts per trillion (ppt) aflatoxin M1. A ROSA reader quantitatively interpreted test strips with ppt readings. Readings < or = 400 ppt were interpreted as negative, and readings >400 ppt were interpreted as positive. Initial positive samples were subsequently assayed 2 additional times. If both retest results were >400 ppt, the sample was called positive/ actionable relative to U.S. and Codex levels, 500 ppt. The concentration of 400 ppt was chosen for the positive/negative interpretation to provide 90% sensitivity with 95% confidence at the 500 ppt legislative level. The combined false negative rate was <5% (4 of 83) for samples at 500 and 550 ppt. The false violatives at 0, 300, 350, 400, and 450 ppt (n = 42 at each level) were 0, 0, 21, 14, and 93%, respectively. The 90% positive concentration with 95% confidence was 503 ppt by probit analysis. The average intralaboratory repeatability was 11% and average interlaboratory reproducibility was 13% for the fortified sample pairs. High-performance liquid chromatography analysis of the study samples by 5 laboratories showed 38% false negatives with the 500 and 550 ppt samples, and a 0% false-violative rate with samples less than the 500 ppt action level.     

Determination of geosmin and 2-methylisoborneol in water and wine samples by ultrasound-assisted dispersive liquid-liquid microextraction coupled to gas chromatography-mass spectrometry

A fast, simple and environmentally friendly ultrasound-assisted dispersive liquid–liquid microextraction (USADLLME) procedure has been developed to preconcentrate geosmin and 2-methylisoborneol (MIB) from water and wine samples prior to quantification by gas chromatography–mass spectrometry (GC–MS). A two-stage multivariate optimization approach was developed by means of a Plackett–Burman design for screening and selecting the significant variables involved in the USADLLME procedure, which was later optimized by means of a circumscribed central composite design. The optimum conditions were: solvent volume, 8 μL; solvent type: tetrachloroethylene; sample volume, 12 mL; centrifugation speed, 2300 rpm; extraction temperature 20 °C; extraction time, 3 min; and centrifugation time, 3 min. Under the optimized experimental conditions the method gave good levels of repeatability with coefficient of variation under 11% (n = 10). Limits of detection were 2 and 9 ng L⁻¹ for geosmin and MIB, respectively. Calculated calibration curves gave high levels of linearity with correlation coefficient values of 0.9988 and 0.9994 for geosmin and MIB, respectively. Finally, the proposed method was applied to the analysis of two water (reservoir and tap) samples and three wine (red, rose and white) samples. The samples were previously analyzed and confirmed free of target analytes. Recovery values ranged between 70 and 113% at two spiking levels (0.25 μg L⁻¹ and 30 ng L⁻¹) showing that the matrix had a negligible effect upon extraction. Only red wine showed a noticeable matrix effect (70–72% recovery). Similar conclusions have been obtained from an uncertainty budget evaluation study.     

Determination of musty odorants, 2-methylisoborneol and geosmin, in environmental water by headspace solid-phase microextraction and gas chromatography--mass spectrometry.

A simple and sensitive method for the determination of musty odorants, 2-methylisoborneol (MIB) and geosmin (GSM), in environmental water was developed by headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry. MIB and GSM were separated within 10 min using a DB-1 capillary column and detected in the selective ion monitoring mode. HS-SPME using a polydimethylsiloxane/divinylbenzene fiber provided effective sample enrichment, and was carried out by fiber exposition at 70 degrees C for 30 min. Using this method, the calibration curves of MIB and GSM were linear in the range of 0-500 pg/mL, with a correlation coefficient above 0.9977 (n=24). The detection limits (S/N=3) of MIB and GSM were 0.9 and 0.6 pg/mL, respectively. This method was successfully applied to the analysis of environmental water samples without interference peaks.     

槟榔中槟榔碱和槟榔次碱的毛细管电泳分析

建立了槟榔中槟榔碱和槟榔次碱的毛细管电泳分析方法。考察了电解质溶液ｐＨ值变化对分离的影响,在选定实验条件下,槟榔碱和槟榔次碱得到了很好的分离,整个分析过程在１０ｍｉｎ内完成,其中槟榔碱和槟榔次碱的迁移时间相对标准偏差在０．４％￣０．７％之间,峰面积的相对标准偏差在３．４％￣３．８％之间。用于实际样品测定,结果满意。     

Analysis of off-flavors in the aquatic environment by stir bar sorptive extraction–thermal desorption–capillary GC/MS/olfactometry

The off-flavor compounds 2-methylisoborneol (MIB), geosmin, 2,4,6-trichloroanisole, 2,3,6-trichloroanisole, 2,3,4-trichloroanisole, and 2,4,6-tribromoanisole were analyzed in water samples by stir bar sorptive extraction (SBSE) followed by on-line thermal desorption (TD) capillary GC/MS. Quantification was performed using the MS in the single-ion-monitoring mode (SIM) with 2,4,6-trichloroanisole-D(5 )as internal standard. Quantification limits are 0.1-0.2 ng L(-1) for the haloanisoles, 0.5 ng L(-1) for geosmin, and 1 ng L(-1) for MIB. The relative standard deviations at the quantification limit ranged from 7 to 14.6%. SBSE recovery was evaluated by spiking real water samples and varied from 87 to 117%. More than twenty samples per day can be analyzed by SBSE-TD-capillary GC-MS. The same technique in combination with olfactometry was used to elucidate unknown odorous compounds in water samples.     

Electrospun nanofibers versus drop casting films for designing an electronic tongue: comparison of performance for monitoring geosmin and 2‐methylisoborneol in water samples

Geosmin (GSM) and 2‐Methylisoborneol (MIB) are substances commonly found in river water and arise due to eutrophication process. Such contaminants affect the organoleptic properties of water, hampering its consumption, and use in beverage industries. As the human perception threshold for these compounds is low, the devices aimed at their detection must be sensitive enough to detect concentrations as low as a few nanogram per liter in order to guarantee the water quality parameters. Due to the experimental simplicity, fast analysis, portability, and capability for on‐site analysis, the use of electronic tongues and electronic noses employing hybrid and composite materials are potential for GSM and MIB determination. In this work, two distinct electronic tongues were applied in the electrical determination of GSM and MIB in pure and river water. The difference between them consisted in the type of polymer processing used in the fabrication of sensing units. The thin films deposited onto gold IDEs were based on polyamide 6, polypirrole, and polyaniline, but fabricated by drop‐casting and electrospinning. The differences in the electronic tongue performances were correlated to the distinct morphologies of the sensitive layers. Both devices were able to discriminate pure water from solutions tainted with GSM and MIB in concentration as low as 25 ng L^?1, with high data correlation and a good reproducibility.     

Improvement of a cryogenic preconcentration unit for C2 - C6 hydrocarbons in ambient air at ppt levels

A previously described method for the quantitative analysis of C₂ - C₆ hydrocarbons in the ppt range based on cryogenic preconcentration has been improved further. Problems caused by condensation of O₂ and traces of water from the sample were overcome using a modified dyring procedure and a tandem preconcentration trap. In addition, the flow path through the unit was simplified further. Technical details are given. The reproducibility of both quantitative results and retention times was improved by these modifications. Typical standard deviations were in the order of 2% at the 200 ppt level.     

C2-C8 hydrocarbon measurement and quality control procedures at the Global Atmosphere Watch Observatory Hohenpeissenberg

A new automated on-line GC-flame ionization detection system for long-term stationary measurements of atmospheric C2-C8 hydrocarbons in the lower ppt range is described. The system is operated at the Global Atmosphere Watch Observatory Hohenpeissenberg (47 degrees 48'N, 11 degrees 01'E) in rural south Germany. Atmospheric mixing ratios of more than 40 different hydrocarbons can be continuously measured in 80 min time intervals. Corresponding detection limits are below 3 ppt, except for propene, butenes and benzene (about 10 ppt). Detailed quality assurance and quality control protocols are described which are applied to routine operation and data analysis. The various error contributions, overall precision, and accuracy for all measured compounds are discussed in detail. Typical ambient air mixing ratios are in the range of a few ppt to a few ppb, and corresponding measurement accuracies are below 10% or 10 ppt. For less than 20% of the analyzed compounds measurement accuracies are worse, mainly because of insufficient peak separation, blank values or reduced reproducibilities. The present system was tested in international intercomparison experiments (NOMHICE, AMOHA). For most of the C2-C8 hydrocarbons analyzed, our results agreed better than +/- 10% (20% NOMHICE phase 5) or +/- 10 ppt with the corresponding reference values.     

Enhancing micro-scale membrane extraction by implementing a barrier film

Hollow fiber based microextraction techniques have shown much promise in the extraction and preconcentration of analytes. Typically, a solvent held in the membrane is used as an extractant (or an acceptor). However, the acceptor also permeates out during long extractions and vigorous agitation. The stabilization of the acceptor is important for high enrichment and good reproducibility. Coating the membrane with a low permeability barrier film can provide diffusional resistance to reduce the outflow of the acceptor. Several compounds were evaluated as potential barrier films. They were found to protect the organic acceptor and significantly enhance extraction performance. In a study with six polycyclic aromatic hydrocarbons (PAHs), enrichment factors ranged between 494 and 4555 were obtained and the detection limits were at low ppb to ppt levels. Good reproducibility with RSDs between 1.60 and 7.65%, and large linear dynamic ranges with good linearity (R2 between 0.9870 and 0.9997) were also achieved.     

Simultaneous determination of free carnitine and total choline by liquid chromatography/mass spectrometry in infant formula and health-care products: single-laboratory validation

A single-laboratory validation study was conducted for a liquid chromatographic/mass spectrometric (LCIMS) method for the simultaneous determination of the free carnitine and total choline in milk-based infant formula and health-care products. The sample preparation used for both carnitine and choline was adapted from AOAC Official Method 999.14, with an acidic and enzymatic hydrolysis of esterified forms of choline. Carnitine and choline were quantified by ion-pair chromatography with single-quadrupole MS detection, using their respective deuterated internal standards. The repeatability relative standard deviation was < or =2.5 and 2.1%, respectively, for carnitine and choline. The intermediate reproducibility relative standard deviation was <4.7 and 2.4%, respectively, for carnitine and choline. The ranges of the average product-specific recoveries were 92-98 and 94-103%, respectively, for carnitine and choline. Choline concentration determined in infant formula reference material SRM 1846 was in agreement with the reference value. The proposed method was compared with the enzymatic methods for a range of products; good correlation (r = 0.99) was obtained, although a significant bias was observed for both analytes. The method, with a short chromatographic run time (7 min), is convenient for routine analysis to enhance analytical throughput and is a good alternative to enzymatic assays.     

Flow injection amperometric detection of ascorbic acid using a Prussian Blue film-modified electrode

The PB film-modified electrode was used as an amperometric detector for flow injection analysis of ascorbic acid. The modified electrode detector showed good sensitivity, stability and reproducibility. The calibration curve for ascorbic acid was linear over the concentration range from 5.0x10(-6) to 1.0x10(-3) mol l(-1) with a slope of 19.9 mA mol(-1) per litre and a correlation coefficient of 0.999. The detection limit of this method was 2.49x10(-6) mol l(-1). The relative standard deviation of six replicate injections of 2.5x10(-4) mol l(-1) ascorbic acid was 2.5%. The results obtained for ascorbic acid determination in pharmaceutical products are in good agreement with those obtained by using the procedure involving the reaction between triiodide and ascorbic acid.     

Chemiluminescence Sensor for the Determination of Hydroxylamine by Electrostatically Immobilizing Luminol and Periodate

IntroductionAnalytical methods based on chemilumi-nescence( CL ) reactions have received considerableattention for theirapplication in various fields,ow-ing to their extremely high sensitivity along withother advantages such as wide linear dynamicrange,simple instrumentation,easy miniaturiza-tion and coupling to various separation tech-niques[1— 6] .CL sensors have been developed for be-ing used as the continuous and real- time monitorsof inorganic,organic,biological and pharmaceuti-cal comp…     

Prediction of FCC gasoline octane numbers using FT-MIR and PLS

A method for predicting "octane numbers" (RON and MON) in fluid catalytic cracking (FCC) gasolines is proposed. Using FT-MIR and PLS, improvements have been obtained in sample throughput, reduced delay times, accuracy (repeatability and reproducibility), amounts of samples and reagents and environmental working conditions when compared with current standard methods. A total number of 140 daily production samples were taken; and from there, a learning group was prepared (44 samples); a validation set (96 samples) was prepared, as well. Sample spectra were recorded from 4000 to 600 cm(-1) at 4 cm(-1) intervals (traditional sealed NaCl cells). The PLS technique was used in its two variants (1 and 2-block). Both provided similar results. Their predictive characteristics are very good: SEP(RON)=0.38; SEP(MON)=0.40; repeatability <0.1 O.N.; reproducibility <0.3 O.N. (SEP=Standard Error of Prediction).     

注塑型聚甲基丙烯酸甲酯多通道微流控芯片的研制及其性能考察

微流控芯片技术因具有微量、快速、高效和高通量等特点,已成为分析化学领域中的研究热点之一．在微流控芯片中,最常见的可用作芯片的材料为玻璃、石英和各种塑料．玻璃和石英有很好的电渗性和光学性质,可采用标准的刻蚀工艺加工和用化学方法进行表面改性,但加工成本较高,封接难度较大．     

Differential pulse voltammetric assay of lercanidipine in tablets

Lercanidipine in ethanol-0.04M Britton-Robinson buffer (20 + 80) gives an irreversible anodic response on a glassy carbon electrode in a broad pH range (2-12) that depends on pH. This signal can be attributed to oxidation of the 1,4-dihydropyridine ring to give the corresponding pyridine derivative. For analytical purposes, differential pulse voltammetry at pH 4 was selected. Under these conditions, good values of both within- and interday reproducibility were obtained, with coefficient of variation (CV) values of 1.56 and 1.70%, respectively, for 10 successive runs. For quantitation, the calibration curve method was used for lercanidipine concentrations ranging from 1 x 10(-5) to 1 x 10(-4) M. The detection and quantitation limits were 1.39 x 10(-5) and 1.49 x 10(-5), respectively. A liquid chromatographic method with electrochemical detection was used for comparison. The voltammetric method showed good selectivity with respect to both excipients and degradation products. The recovery study exhibited a CV of 0.94% and an average recovery of 98.3%, and it was not necessary to treat the sample before the analysis. The method was successfully applied to the individual tablet assay of lercanidipine in commercial tablets.     

Geosmin biosynthesis. Streptomyces coelicolor germacradienol/germacrene D synthase converts farnesyl diphosphate to geosmin

Geosmin is responsible for the characteristic odor of moist soil. Incubation of recombinant germacradienol synthase, encoded by the SCO6073 (SC9B1.20) gene of the Gram-positive soil bacterium Streptomyces coelicolor, with farnesyl diphosphate (2, FPP) in the presence of Mg2+ gave a mixture of (4S,7R)-germacra-1(10)E,5E-diene-11-ol (3) (74%), (-)-(7S)-germacrene D (4) (10%), geosmin (1) (13%), and a hydrocarbon, tentatively assigned the structure of octalin 5 (3%). Individual incubations of recombinant germacradienol synthase with [1,1-2H2]FPP (2a), (1R)-[1-2H]-FPP (2b), and (1S)-[1-2H]-FPP (2c), as well as with FPP (2) in D2O, and GC-MS analysis of the resulting deuterated products supported a mechanism of geosmin formation involving proton-initiated cyclization and retro-Prins fragmentation of the initially formed germacradienol to give intermediate 5, followed by protonation of 5, 1,2-hydride shift, and capture of water.     

Simultaneous determination of eight common odors in natural water body using automatic purge and trap coupled to gas chromatography with mass spectrometry

Production and fate of taste and odor (T&O) compounds in natural waters are a pressing environmental issue. Simultaneous determination of these complex compounds (covering a wide range of boiling points) has been difficult. A simple and sensitive method for the determination of eight malodors products of cyanobacterial blooms was developed using automatic purge and trap (P&T) coupled with gas chromatography-mass spectrometry (GC-MS). This extraction and concentration technique is solvent-free. Dimethylsulfide (DMS), dimethyltrisulfide (DMTS), 2-isopropyl-3-methoxypyrazine (IPMP), 2-isobutyl-3-methoxypyrazine (IBMP), 2-methylisoborneol (MIB), β-cyclocitral, geosmin (GSM) and β-ionone were separated within 15.3 min. P&T uses trap #07 and high-purity nitrogen purge gas. The calibration curves of the eight odors show good linearity in the range of 1-500 ng/L with a correlation coefficient above 0.999 (levels=8) and with residuals ranging from approximately 83% to 124%. The limits of detection (LOD) (S/N=3) are all below 1.5 ng/L that of GSM is even lower at 0.08 ng/L. The relative standard deviations (RSD) are between 3.38% and 8.59% (n=5) and recoveries of the analytes from water samples of a eutrophic lake are between 80.54% and 114.91%. This method could be widely employed for monitoring these eight odors in natural waters.     

稳定性同位素稀释吹扫捕集-气质联用法测定水中典型臭味物质

采用稳定性同位素稀释吹扫捕集-气相色谱/质谱联用法测定水中典型臭味物质土臭素(GSM)和2-甲基异莰醇(MIB).研究了特征离子、升温程序、样品吹扫温度及盐浓度等因素对臭味物质萃取过程的影响.本实验测定臭味物质的最佳条件为:盐浓度20%(m/V),样品吹扫温度60℃,程序升温速率5℃/min.通过加人同位素内标d5-G...     

Analysis of light hydrocarbons (C2?C6) at PPT levels by high resolution gas chromatography

An analytical technique is described which allows the determination of C₂? C₆ hydrocarbons in the ppt-range from up to 21 air samples after removal of air humidity. Preconcentration is carried out on a two stage cryotrap system. The compounds are separ ated on a temperature-programmed capillary coated with Al₂ O₃. Detection limits (S/N 2:1) of 1.5 to 5 ppt were obtained for air samples from the Arctic. The reproducibility of the method was about 3% at the 50–100 ppt level. Practical problems are discussed in detail.