Characterization of Polyethylene in Dibutoxymethane by High-Temperature Gel Permeation Chromatography with Triple Detection

This study presents the possibility of replacing the 1,2,4-trichlorobenzene (TCB) recommended by ASTM D 6474 for the analysis by gel permeation chromatography (GPC) of linear polyethylenes with dibutoxymethane (DBM, butylal), a halogen-free and less toxic solvent. The molecular weight distributions as well as the K and alpha parameters of the Mark-Houwink-Sakurada relationship were measured for polyethylene solutions in TCB and DBM, using a GPC system with triple detection (light scattering, differential refractive index, and viscometer). For commercial metallocene polyethylene resins typically used for film and packaging applications, the GPC method in DBM provided results comparable to those obtained in TCB.     

便携式气相色谱仪测定海上平台天然气中氮气含量

为保障海上平台安全生产,采用便携式色谱仪对海上平台天然气中氮气进行分析.便携式色谱仪利用气相色谱原理能够准确分析产出气体组成.仪器检测数据精度高,检测速度快,单个样品检测时间为4 min,可连续工作时间为8 h.现场检测表明便携式色谱仪具有操作简单、快速等特点,对快速判定气体成分显示出一定的优越性,为海上油气田天然气中氮气快速检测提供技术支持.     

Fast Analytical Temperature Rising Elution Fractionation (TREF) of Polypropylenes

Analytical temperature rising elution fractionation (TREF) is a complementary technique of gel permeation chromatography (GPC) for the analysis of polyolefin structure. By connecting a high-temperature GPC with a gas chromatograph (GC) oven it is possible to build a fast analytical TREF, which permits a dramatic reduction in analysis time by directly injecting the polymer solution onto the cold column, as compared with the traditional TREF in which the slow cooling step usually takes more than 40 h. The method was successfully applied on six commercial random and homo polypropylenes for which similar thermograms were obtained for fast- and slow-cooling TREF. The obtained results show subtle differences in the behavior of polypropylene melting in solution as compared with previously analyzed polyethylene. The most important is the difference of 12.6°C between the melting temperatures in the presence of trichlorobenzene and xylene, which is much higher for polypropylene than the 3.7°C measured for polyethylene.     

反相高效液相色谱法测定补钙保健品中的维生素D_3

 用氯仿作提取剂直接提取补钙保健品中的维生素Ｄ３,提取液经浓缩后进行高效液相色谱分析,并对皂化和直接提取的样品中维生素Ｄ３的含量进行了比较。采用μ－ＢｏｎｄａｐａｋＣ１８作分离柱,甲醇－水（８７１３）作流动相,检测波长为２６４ｎｍ,回收率为９５．６３％。     

High performance liquid chromatography of glucose using a post-column reactor of immobilized enzyme followed by electrochemical detection (glucose-LCEC)

A sensitive and selective, reasonably fast method for the determination of glucose content has been developed. A glucose oxidase immobilized column was coupled to a small-size anion exchange column/borate buffer chromatograph. The hydrogen peroxide produced in the enzyme reaction was detected directly by an amperometric detector using a platinum working electrode. The detection limit was 0.03 ppm (1.5 x 10(-7) M, 3 pmol/injection). The linear dynamic range was three orders of magnitude at least. The system was stable and reproducible both in short- and long-term operation. The proposed method is suitable for analysis of complicated matrices of biological samples because of its good selectivity and sensitivity.     

Multilaboratory validation of a method to confirm chloramphenicol in shrimp and crabmeat by liquid chromatography-tandem mass spectrometry

An existing method for chloramphenicol (CAP) determination in shrimp using a gas chromatograph with electron capture detector was adapted for confirmation of CAP with a liquid chromatograph interfaced to a triple quadrupole mass spectrometer. CAP residues are extracted from tissue with ethyl acetate, isolated via liquid-liquid extraction, and concentrated by evaporation. Extracts are chromatographed by using a reversed-phased column and analyzed by electrospray negative mode tandem mass spectrometry. Four product ions (m/z 152, 176, 194, and 257) of precursor m/z 321 were monitored. Moving from gas chromatography to liquid chromatography-tandem mass spectrometry improved the sensitivity of the method greatly, enabling reliable confirmation of CAP residues at 0.3 microg/kg (ppb). The method meets confirmation criteria recommended by the U.S. Food and Drug Administration and 4-point identification criteria established by the European Union. With slight modifications to accommodate different equipment, the method was validated in 3 laboratories.     

Analytical temperature rising elution fractionation of different polyethylene types using a column filled with carbon nanotubes

A high temperature gel permeation chromatograph (GPC) was coupled with a gas chromatograph (GC) oven to obtain an analytical temperature rising elution fractionation (TREF) system with evaporative light scattering detection. On this instrument, a new column partially filled with pristine carbon nanotubes (CNT) was tested by evaluating the elution profiles in function of temperature (thermograms) of different polyethylene (PE) types. By comparing these thermograms with those obtained with a traditional TREF column filled with metallic wires, the adsorption of polymer chains on the pristine CNT was clearly evidenced. The thermograms given by the column filled with CNT are similar with those provided by literature when chromatographic columns filled with porous graphitic carbon are used for this application, usually described as high temperature thermal gradient interaction chromatography (HT-TGIC).     

Determination of atrazine, deethylatrazine and simazine in water at parts-per-trillion levels using solid-phase extraction and gas chromatography/ion trap mass spectrometry

Methods for trace analysis of atrazine and simazine in water have been developed by using stable-isotope dilution with detection by gas chromatography/mass spectrometry. D(5)-Atrazine was used as the internal standard for the determination of atrazine and deethylatrazine, while (13)C(3)-simazine was used for simazine analysis. Water samples were fortified with known amounts of the internal standards and submitted to solid-phase extraction with a C(18) bonded-silica cartridge. A gas chromatograph coupled with an ion-trap mass spectrometer was used to analyze the water sample extracts. Method detection limits were 38 parts-per-trillion (ppt) for atrazine and deethylatrazine and 75 ppt for simazine. The accuracy of the method, represented by relative analytical errors, was less than 15%, and the method precision was less than 5% (relative standard deviation, n = 9). The method was successfully applied to analyze surface water samples collected from a reservoir and a river at ppt levels.     

Determination of PCDD/Fs and dioxin-like PCBs in food and feed using gas chromatography-triple quadrupole mass spectrometry

A method was developed on a gas chromatograph coupled to a triple quadrupole mass spectrometer(GC-MS/MS) for trace level determination of polychlorinated dibenzo-p-dioxins/dibenzofurans(PCDD/Fs) and dioxin-like polychlorinated biphenyls(DL-PCBs) in food and feed. The results demonstrated good sensitivity and repeatability for PCDD/Fs and DL-PCBs at an extremely low level(10 pg mL~(-1) for 2,3,7,8-TCDD/F), as well as wide linear response of over 3 or 4 orders of magnitude in concentration ranges; 0.5–200 ng mL~(-1) for PeCDD/F and 0.2–2000 ng mL~(-1) for DL-PCBs. The method detection limits for PCDD/Fs and DL-PCBs were in the range from 0.018–0.17 pg g~(-1) to 0.13–0.36 pg g~(-1), respectively. The performance of the GC-MS/MS for food and feed sample analysis showed high precision and accuracy compared to the high resolution gas chromatograph/high resolution mass spectrometer. The results indicated the feasibility of GC-MS/MS as a confirmatory method for the measurement of PCDD/Fs and DL-PCBs in food and feed as required by European Union legislation.     

Screening method for polycyclic aromatic hydrocarbons in soil using hollow fiber membrane solvent microextraction

A fast, inexpensive screening method for polycyclic aromatic hydrocarbons in soil has been developed. Using hollow fiber membrane solvent microextraction, 8 microl of octane extraction solvent was placed inside a porous, polypropylene fiber. Following an 8 min analyte preconcentration step, 4 microl of extract was injected into a gas chromatograph. Separation was achieved in less than 10 min with a detection limit of 0.13 mg/kg for 2-methylnaphthalene. Results of both spiked and real soil samples are presented.     

红枣中果糖、葡萄糖与蔗糖的高效液相色谱示差检测分析

建立了同时分析鲜红枣中果糖、葡萄糖和蔗糖的高效液相色谱方法.利用鲜红枣样品进行添加回收实验,获得方法对果糖、葡萄糖和蔗糖测定的平均回收率分别为93.5%、91.8%和89.8%,变异系数3.27%、2.34%、5.86%.结果表明:采用高效液相色谱示差分析方法定量检测鲜红枣中果糖、葡萄糖和蔗糖快速、简便.同时得出方法的检出限为:果糖5.73×10-3mg/mL,葡萄糖5.22×10-3mg/mL,蔗糖3.59×10-3mg/mL,测定结果符合食品检测要求.     

Separation and characterisation of five polar herbicides using countercurrent chromatography with detection by negative ion electrospray ionisation mass spectrometry.

Five polar herbicides were separated and characterised using high-speed analytical countercurrent chromatography (HSACCC) in conjunction with online electrospray mass spectrometry (ESI-MS). The countercurrent chromatography used a standard isocratic biphasic solvent system of hexane/ethyl acetate/methanol/water in reverse phase to effect the separation of these five environmentally important compounds. The chromatograph was coupled to a triple quadrupole mass spectrometer via a standard electrospray liquid chromatography interface that was able to give mass spectra in negative ion mode of each compound. Limits of detection are reported for this series of compounds along with representative negative ion ESI-MS data and calibrations for the separation.     

Construction and validation of an automated spray-and-trap gas chromatograph for the determination of volatile organic compounds in aqueous samples

An automated spray-and-trap (ST) chromatographic system was constructed for fast and efficient extraction of volatile organic compounds (VOCs) in aqueous samples with the capability to be deployed in the field for unattended continuous monitoring of surface or ground water. This system was built upon a commercial gas chromatograph with full automation capability using self-developed hardware and software. For sample analysis, fine droplets of the aqueous solution were generated in the extraction chamber by pressure expansion of a clean air stream through a spray nozzle. A portion of the VOCs distributed into the gas phase was retained by a multi-sorbent micro-trap kept at ambient temperature. Flash heating of the sorbent trap desorbed the enriched VOCs onto the gas chromatography (GC) with flame ionization detection (FID) for hydrocarbons or electron-capture detection (ECD) for halocarbons. In order to validate the performance of the ST method. it was compared with a more conventional method, i.e., a purge-and-trap (PT), by analyzing a serious of standard solutions containing benzene, toluene, ethylene. and o-, m-xylenes. Using a purge-and-trap method as a reference for complete extraction, the ST method showed less sensitivity. Extraction recoveries are in consistent with Henry's law constants. To test response time the ST-GC-ECD was periodically switched between tap and underground waters. Negligible carry-over of halogenated species and reproducibility better than 2% relative standard deviation (R.S.D.) can be achieved regardless of large concentration difference between the two sources, thus demonstrating applicability of the ST system for on-site monitoring.     

Determination of N-nitrosodimethylamine in fish products using gas chromatography with nitrogen-phosphorus detection

A simple and rapid gas chromatographic method for the determination of N-nitrosodimethylamine (NDMA) in fish products is described. NDMA is extracted from a dried sample with methylene chloride, mixed with n-hexane and passed through a silica gel column. NDMA adsorbed on silica gel is eluted with methylene chloride-diethyl ether (7:3) and the eluate is passed through a Sep-Pak alumina A cartridge column, on which NDMA is adsorbed. NDMA is eluted from the cartridge with diethyl ether-methanol (2:1) and the solution is injected into a gas chromatograph with nitrogen-phosphorus detection. This method does not use solvent evaporation and concentration in the clean-up procedure, which eliminates the loss of volatile NDMA and artifactual formation of NDMA in the analytical procedure. The detection limit is 0.5-1 micrograms/kg and recoveries from salted pollack roe spiked at 40 and 4 micrograms/kg were 96.7% [relative standard deviation (R.S.D.) 3.6%] and 85.0% (R.S.D. 6.8%) respectively.     

Development and optimization of an LC-MS/MS-based method for simultaneous quantification of vitamin D2 , vitamin D3 , 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3

Simultaneous and accurate measurement of vitamin D and 25-hydroxyvitamin D in biological samples is a barrier limiting our ability to define "optimal" vitamin D status. Thus, our goal was to optimize conditions and evaluate an LC-MS method for simultaneous detection and quantification of vitamin D(2) , vitamin D(3) , 25-hydroxyvitamin D(2) and 25-hydroxyvitamin D(3) in serum. Extraction and separation of vitamin D forms were achieved using acetone liquid-liquid extraction and by a reversed phase C8 column, respectively. Detection was performed on a triple quadrupole tandem mass spectrometer (QQQ-MS/MS) equipped with atmospheric pressure photo ionization source. The LOQs for all analytes tested were 1 ng/mL for hydroxylated molecules and 2 ng/mL for the parent vitamin Ds. RSD at lower LOQ (2 ng/mL) and in medium (80 ng/mL) and high (200 ng/mL) quality control samples did not exceed 20 and 15% CV, respectively. Accuracy of the method for determination of hydroxylated molecules was also validated using National Institutes of Standards and Technology standard samples and found to be in the range of 90.9-111.2%. In summary, a sensitive and reproducible method is reported for simultaneous quantification of vitamin D(2) , vitamin D(3) , 25-hydroxyvitamin D(2) and 25-hydroxyvitamin D(3) molecules in biological samples.     

反相高效液相色谱-增敏化学发光同时测定VB1和VC

本文基于维生素B1(VB1)、维生素C(VC)对鲁米诺(Luminol)和铁氰化钾(K3[Fe(CN)6])化学发光反应的增敏作用原理,建立了反相高效液相色谱(RP-HPLC)分离、柱后化学发光检测VB1与VC的新方法。当在鲁米诺中加入KBr时可以大大增敏该反应。本法已成功运用于蜂蜜和复合维生素片中VB1与VC的测定。     

A biostimulation-based accelerated method for evaluating the biodegradability of polymers

The high cost and long duration of the existing standard tests, such as ASTM D5338 and ISO 14855, represents an important drawback in evaluating the biodegradability of polymers. This works presents a new accelerated method for this purpose, based on the use of a Bartha respirometer and biostimulation with yeast extract. The new method was applied to microcrystalline cellulose (MCC), low density polyethylene (LDPE), poly(3-hidroxybutyrate) (PHB), poly(lactic acid) (PLA), poly(vinyl alcohol) (PVOH), polypropylene (PP) and poly(ethylene terephthalate) (PET). The results obtained with these polymers were consistent with those of the standard methods in terms of differentiating biodegradable and non-biodegradable polymers and relative order of biodegradation extent. Besides, a significant reduction of test duration was achieved (from 45 to 110 days with ASTM D5338 or ISO 14855 to 28 days). These results corroborate the potential of the proposed method as a fast test for assessment of biodegradation of polymeric materials.     

In situ solvent formation microextraction combined with magnetic dispersive micro‐solid‐phase extraction for the determination of benzoylurea insecticides in water samples

A simple, fast, effective, and environmentally friendly method, in situ solvent formation microextraction combined with magnetic dispersive micro‐solid‐phase extraction for the determination of four benzoylurea insecticides is presented herein for the first time. In the proposed method, 1‐hexyl‐3‐methylimidazolium bis[(trifluoromethane)sulfonyl]imide was formed by the reaction between 1‐hexyl‐3‐methylimidazolium chloride and lithium bis[(trifluoromethane)sulfonyl]imide and was used to extract benzoylurea insecticides. Then magnetic nanoparticles were added as carrier to retrieve and separate the ionic liquid from the sample solution. After the supernatant was removed, the ionic liquid was desorbed using acetonitrile and subsequently injected directly into a high‐performance liquid chromatograph equipped with a variable wavelength detector for analysis. The main factors affecting the extraction efficiency were investigated by a one factor at a time approach. Under optimized conditions, the proposed method showed good repeatability (RSD = 2.2–4.5%) and linearity (2–300 μg/L), with correlation coefficients greater than 0.9994 and low limits of detection (0.67–1.46 μg/L). Finally, the method was successfully applied to the analysis of four benzoylurea insecticides in environmental water samples with good recoveries (73.2–85.8%).     

Determination of trihalomethanes in soil matrices by simplified quick,easy, cheap,effective, rugged and safe extraction and fast gas chromatography with electron capture detection

A method based on QuEChERS extraction is proposed for the determination of trihalomethanes (chloroform, bromodichloromethane, dibromocloromethane and bromoform) in soil samples. The new version of QuEChERS adapted to soil samples consists of liquid extraction with ethyl acetate, the addition of water to moisten the samples, salting-out partitioning of the water with anhydrous MgSO₄, and direct injection of the organic extract, obtained after the centrifugation step, into the gas chromatograph. This simplified extraction procedure maintains the advantages of the original method and avoids some steps, making the final procedure simpler, faster, and cheaper, with the consequent reduction in errors associated with sample manipulation. The experimental conditions of the analytical method, based on fast gas chromatography (FGC) and micro-electron capture detection (μECD), were optimized. The column and oven program used allowed fast separation of the compounds in less than 4 min and the total analysis cycle time was as short as 10 min. The existence of a matrix effect was checked and the analytical conditions of the method were studied in a fortified garden soil sample. The highly sensitive and selective detector used afforded to detection limits in the order of ng/kg for the target compounds. To validate the proposed method two certified reference materials (CRMs) were analyzed.     

HPLC determination of neopterin in biological liquids for clinical purposes

A HPLC method is proposed for determining neopterin in biological liquids. The method was realized using a standard chromatographic instrumentation. Neopterin was isolated from blood serum and urine by solid-phase extraction on cartridges containing 30 mg of supercrosslinked polystyrene. The separation was carried out on an Irica chromatograph (Japan) equipped with means of UV (350 nm) and fluorimetric (es350-em430 nm) detection. The degree of extraction was 96–113%, and the sensitivity of UV and fluorimetric detection was 0.1 and ～0.03 ng, respectively (at signal-to-noise ratio 3). It is shown that the method is suitable for use in routine clinical analysis of neopterin in biological liquids.