Uncertainties of gas chromatographic measurement of troublesome pesticide residues in apples employing conventional and mass spectrometric detectors

In recent years the declaration of estimated uncertainty of measurement has become an integral part of analytical results. This study presents the assessment of results generated within the analysis of selected pesticides represented by carbamates, pyrethroides and azoles, residues of which may be found in treated apples. Multiresidue method used for analysis of spiked samples (residues at levels 0.040–0.163 mg/kg) consisted of (i) ethyl acetate extraction, (ii) GPC clean-up and (iii) identification/quantification of residues by GC. Procedures utilizing either conventional (electron-capture, nitrogen–phosphorus) or mass-selective detectors (quadrupole and ion trap analyzer) were evaluated. The results generated through alternative strategies of uncertainty estimation (“bottom-up”, “top-down”) were compared.

Using the “bottom-up” approach uncertainty of extraction which comprises two components—(i) repeatability of extraction and (ii) uncertainty of extraction recovery was shown to represent the main source of combined standard uncertainty (values of uncertainty of extraction for tested pesticides ranged from 4.6% to 21.6%). On the other hand, uncertainties associated with the GC calibration (uncertainties of weighing and diluting standards, uncertainties of purity of standards) were not so important (most of them did not exceed 2%). Combined standard uncertainties associated with the described analytical method ranged for individual compounds from 9.3% to 24.3%. Similar values of combined standard uncertainties were obtained using the alternative “top-down” approach.     

Visible spectrophotometric determination of tantalum in soil, sediment, minerals, and alloys

A new, sensitive, and selective method is described for the spectrophotometric determination of Ta(V). The method is based on the extraction of the Ta(V)-F-CV+ complex (CV+ = crystal violet cation) with a benzene solution of imidoyl derivatives (ID), i.e., N,N'-diphenylbenzamidine (DPBA), N-hydroxy-N,N'-diphenylbenzamidine, and N-(2,5-dimethyl)phenyl-p-tolylimidoylphenylhydrazine, from sulfuric acid solution; DPBA was selected for detailed study. The molar absorptivities of the Ta(V)-F-CV+-ID complexes in the benzene solution were in the range of (1.00-1.65) x 10(5) L/mol x cm at 600 nm. The limit of detection was 7 ng Ta/mL (which had an absorbance greater than that of the blank + 3 standard deviations). The optimization of the analytical variables, the composition of the complex, and the effect of diverse ions in the determination of Ta are discussed. The present method was applied to the determination of Ta in environmental samples, i.e., soil, sediment, minerals, and alloys.     

气相色谱法测定土壤中酰胺类除草剂

建立了从土壤中同时提取甲草胺、乙草胺和丁草胺并采用气相色谱法测定的分析方法.采用丙酮-石油醚(2:1,V/V)为提取液,经弗罗里矽硅土固相萃取柱净化,超声30 min、振荡10 min.测定结果显示,甲草胺、乙草胺、丁草胺的保留时间分别为16.333,16.019,20.249 min;线性相关系数>0.9990;6个...     

Validation of a method for arsenic speciation in food by ion chromatography-inductively coupled plasma/mass spectrometry after ultrasonic-assisted enzymatic extraction

A fully validated and rapid quantitative method is presented for determination of inorganic arsenic [arsenite, As(III) and arsenate, As(V)] and organic arsenic species (methylarsonic acid, dimethylarsinic acid, and arsenobetaine) by ion chromatography paired with inductively coupled plasma/MS after ultrasonic-assisted enzymatic extraction (UAEE) in rice- and seafood-based raw materials and finished products. This method gives toxicological meaning to arsenic analysis, since the sum of the toxic chemical forms As(III) and As(V) can be determined. In contrast to classical water-methanol extraction, UAEE enables drastic acceleration of sample extraction (5 min instead of several hours), while total arsenic extraction efficiency is improved without species conversion. Validation was performed to evaluate the method for selectivity, linearity, LOD/LOQ (0.007-0.020 mg/kg), trueness, precision (HorRat values, 0.2-0.6), recovery (93-122%), and uncertainty. The method was also satisfactorily tested using two proficiency tests. Performance characteristics are reported for four certified reference materials, standard reference material (SRM) 1568a (rice flour), Institute for Reference Materials and Measurements 804 (rice flour), SRM 2976 (mussel tissue), certified reference material-627 (tuna fish), and several commercial food samples populating five AOAC triangle food sectors. The results indicated that this speciation method is cost-efficient, time-saving, and accurate, as well as fit-for-purpose, according to International Organization for Standardization/International Electrotechnical Commission 17025:2005 standard, and could be used for routine analysis.     

Development of a rapid and sensitive method for the simultaneous determination of 1,2-dibromoethane, 1,4-dichlorobenzene and naphthalene residues in honey using HS-SPME coupled with GC-MS

A new method for the simultaneous determination of 1,4-dichlorobenzene (p-DCB), naphthalene and 1,2-dibromoethane (1,2-DBE) residues in honey has been developed. Analysis is carried out using gas chromatography-mass spectrometry (GC/MS) in selected ion monitoring mode (SIM), after extraction and preconcentration of target analytes by headspace solid-phase microextraction (HS-SPME), with a 100 microm film thickness polydimethylsiloxane (PDMS) fiber. Several parameters affecting the extension of the adsorption process (i.e., addition of salt, extraction time, extraction temperature) were studied. The optimal conditions for the determination of these analytes were established. The proposed HS-SPME method showed good sensitivity, without carryover between the samples. Linearity was studied from 5 to 2500 microg kg(-1) for p-DCB, 0.5 to 500 microg kg(-1) for naphthalene and 5 to 500 microg kg(-1) honey for 1,2-DBE with correlation coefficients (r(2)) ranging from 0.9901 to 0.9999. Precision was assessed and both intra and inter-day R.S.D.s (%) were below 6.3%. The detection limits were found to be 1, 0.1 and 2 microg kg(-1) honey for p-DCB, naphthalene and 1,2-DBE, respectively. The percentage recoveries that were evaluated with the proposed HS-SPME method and the standard addition calibration technique gave values among 72.8 and 104.3% for measurements in samples spiked with one target analyte or mixtures of the three. This method has been applied for the analysis of unknown honey samples. The results showed an excellent applicability of the proposed method for the determination of the target compounds in honey samples.     

固相萃取和高效液相色谱相结合快速测定苦瓜甙A的含量(英文)

 建立了一个快速、简单、准确的固相萃取和高效液相色谱相结合的测定苦瓜甙A含量的方法。样品经石墨碳固相萃取管 (3mL/ 2 5 0mg)纯化后以高效液相色谱检测。色谱柱为C18,流动相为V(乙腈 )∶V(甲醇 )∶V(5 0mmol/L磷酸二氢钾缓冲液 ) =2 5∶2 0∶6 0 ,流速为 0 .8mL/min ,检测波长为 2 0 8nm。标准曲线自 10mg/L到 10 0 0mg/L呈线形关系 (r2 =0 .9992 )。该方法具有很好的重现性 ,日内或日间的相对标准偏差和相对平均误差均小于 10 %。样品回收率大于 90 %。     

Single laboratory validation of a method for the determination of hydroxymethylfurfural in honey by using solid-phase extraction cleanup and liquid chromatography

A method is described for the determination of hydroxymethylfurfural (HMF) in honey. The method, which is based on solid-phase extraction cleanup followed by liquid chromatography (LC) with UV absorbance detection, was tested on a variety of different honey types: liquid, set, blended, filtered, crystalline, and comb honey. A sample of honey fortified with a known amount of HMF acted as an in-house reference material. LC with diode-array detection showed that the HMF peak did not contain any peaks of coeluting interfering species. Stability studies showed that honey samples should not be repeatedly frozen and thawed because the temperature changes caused a gradual increase in the HMF concentration. It was also shown that aqueous HMF standard solutions should be kept in the dark at 4 degrees C to avoid degradation of the HMF. The method was internally validated, and the measurement uncertainty was estimated to be +/-9.0 at 40 mg/kg, the legal limit. A comparison of the relative standard uncertainty with the Horwitz relative standard deviation showed that the method was suitable for its purpose and should be validated by a collaborative trial.     

Estimation of the method evaluation function for the determination of hydride-generating arsenic compounds in urine by flow-injection atomic-absorption spectrometry

A direct flow-injection atomic-absorption spectrometric (FIA-AAS) method for the assessment of inorganic arsenic compounds and their metabolites was developed and statistically evaluated by the estimation of the method evaluation function (MEF), which provides detailed information on the analytical performance of the method, i.e., the average combined uncertainty and the magnitude of potential systematic errors. The method evaluation study demonstrated that the use of standard addition was a necessity to obtain an acceptable method performance at low concentrations typical for low dose exposure. In contrast the use of calibration curves resulted in a method with reduced sensitivity and high systematic error. The developed method, using standard addition, had a limit of detection (2.9 microg/l.) sufficiently low for the determination of hydride-generating arsenic species in urine from non-exposed and low exposed persons. Organoarsenicals such as arsenobetaine and arsenocholine are not detected by this method. Hence, the contribution of these compounds derived from a diet containing seafood does not affect the monitoring of inorganic arsenic compounds after occupational or environmental exposure. The high capacity of the FIA-AAS system (three minutes per sample measured by standard addition) together with the low limit of detection makes this method suitable for biological monitoring of inorganic arsenic exposure even though standard addition is required.     

A comparison of the external standard and standard addition methods for the quantitative chromatographic determination of pesticide concentrations in plant samples

Model samples containing known amounts of pesticides in various plant materials were analyzed, and the accuracies of the external standard and standard addition methods were compared based on a criterion such as the relative analyte concentration. It was found that traditionally recommended procedures for the solvent extraction of pesticides from samples of this kind in combination with quantitative analysis by the external standard method determine only 10–70% of the true concentrations of analytes. This is most likely due to analyte adsorption on matrices and/or incomplete extraction. In almost all cases, the use of the standard addition method compensates pesticide losses at the stages of sample preparation and thereby considerably decreases the systematic error of determination. The extrapolation of analyte concentration to the zero amount of the added reference sample was proposed to additionally control the accuracy of results obtained by the standard addition method. Moreover, it was found that solid-phase extraction as the second stage of sample preparation has no considerable advantages over back solvent extraction in terms of the above criterion. This is because the main analyte losses were observed at the first stage of extraction from test samples.     

Optical fibre chemical sensor for trace vanadium(V) determination based on newly synthesized palm based fatty hydroxamic acid immobilized in polyvinyl chloride membrane

Fatty hydroxamic acid (FHA) immobilized in polyvinyl chloride (PVC) has been studied as a sensor element of an optical fibre chemical sensor for V(V). By using this instrument, V(V) in solution has been determined in the log concentration range of 0-2.5 (i.e. 1.0-300 mg/L). The detection limit was 1.0 mg/L. The relative standard deviation (R.S.D.) of the method for the reproducibility study at V(V) concentration of 200 mg/L and 300 mg/L were calculated to be 2.9% and 2.0%, respectively. Interference from foreign ions was also studied at 1:1 mole ratio of V(V):foreign ions. It was found that, Fe(III) ion interfered most in the determination of vanadium(V). Excellent agreement with ICP-AES method was achieved when the proposed method was applied towards determination of V(V).     

改进的氧瓶燃烧法结合电感耦合等离子体质谱快速测定茶叶样品中的稀土元素含量

建立了电感耦合等离子体质谱法快速测定茶叶中Y~Lu共15种稀土元素的新方法,样品处理基于改进的氧瓶燃烧法,以涂覆甘油的石英布代替滤纸作为引燃和燃烧载体,在500 mL容积燃烧瓶中实现了0.1 g样品量的有氧完全燃烧。系统优化了样品处理关键参数,以5 mL 4％ HNO3+1％ HF(V/V)组合试剂超声提取燃烧残渣1 min,稀土元素回收率大于90％,样品总处理周期小于3 min。6次样品平行测定值的相对标准偏差(RSD)在2.7％~5.5％之间,方法检出限(3σ)在0.001~0.006 mg/kg之间。采用本方法对3种茶叶标准参考物质进行分析,测定结果和标准值吻合良好。     

QuEChERS结合UPLC-M S/M S检测血液中苯丙胺类及其相关9种物质

对QuEChERS前处理方法从提取、分离、净化等方面进行优化以减弱样本中的基质效应,提高灵敏度;使用提取试剂(含0.1%甲酸的乙腈:甲醇=70:30,V/V)进行提取,加入无水硫酸镁、硼酸钠、研磨珠进行提取分离,使用混合净化剂(十八烷基硅烷(C18):乙二胺-N-丙基硅烷(PSA)=1:2,m/m)进行净化,UPLC-MS/MS测定,外标法定量。结果表明:在优化条件下,苯丙胺类及其相关9种物质的色谱峰分离良好,且各标准化合物的线性相关系数均大于0.991,检出限(LODs)为0.3~1.0 ng/mL,定量限(LOQs)均为2.5 ng/mL;血液添加标准品样本在低(20 ng/mL)、中(100 ng/mL)、高(400 ng/mL)3个浓度的加标回收率为80.1%~103.1%,精密度相对标准偏差(RSD)为1.5%~8.6%;临床4份检测样本中有3份检出苯丙胺类阳性,准确率为71.5%~99.1%。所建立的QuEChERS方法与UPLC-MS/MS结合的分析方法可应用于血液样本中苯丙胺类及其相关9种药物的同时检测分析。     

Microwave-assisted extraction and quantitative analysis of high-density polyethylene pellets fortified with flavors

Microwave-assisted extraction (MAE) has been shown to be an easy, rapid, accurate, quantitative, and precise component of an overall method for the quantitative analysis of flavor components formulated into high-density polyethylene (HDPE) pellets. Under optimized extraction conditions, MAE can be perform extraction of flavors from pellets within 1/2 h with flavor recoveries ranging from approximately 90% to 100%. The variability in the data expressed as percent relative standard deviation from gas chromatographic-mass selective detector analysis of targeted flavor components is always less than 5%, indicating a precise method. In addition, the major components identified in the flavor formulation prior to formulation into the HDPE pellets are the major components detected in the extraction, indicating an accurate determination. Thus, MAE can be readily recommended as an essential component of a high-volume approach to the quantitative determination of flavors formulated into HDPE pellets.     

反相高效液相法测定血清中的佐匹克隆

 建立了测定血清中佐匹克隆的反相高效液相法 (外标法 )。血样用正丁基氯提取后进行分离。采用的柱为LiChroCART 12 5 4柱 (LiChrospher 6 0RPselectB填料 ,5 μm ,12 5mm× 4mmi d ) ,流动相为乙腈 0 0 2mol/LKH2 PO4缓冲溶液 (体积比为 2 0∶80 ) ,紫外检测波长为 2 5 4nm。当佐匹克隆在血清中的添加质量浓度分别为 4 0 0 μg/L ,16 0 0 μg/L和6 4 0 0 μg/L时 ,血清中佐匹克隆的回收率分别是 (73 4± 3 2 ) % ,(82 2± 4 1) %和(90 3± 4 5 ) %。方法的最低检出限为 15 μg/L。方法适用于法庭毒物分析 ,简便、快速。     

气相色谱–质谱法测定食用植物油中短链脂肪酸的测量不确定度评定

采用气相色谱–质谱法(GC–MS)测定食用植物油中短链脂肪酸含量,对测量结果的不确定度进行评定,探讨提高测量准确度的方法。依据方法建立数学模型,分析得出不确定度主要来源于样品制备过程、计量器具的使用、标准溶液配制、测量设备、人员读数误差、方法回收率,计算各不确定度分量,得到相对标准不确定度和扩展不确定度。结果表明,当食用植物油中短链脂肪酸测定结果为13.1 mg/kg时,其扩展不确定度为1.8 mg/kg(k=2)。测量设备、标准溶液配制过程引入的不确定度较大,应在实验过程中予以控制和关注。     

Extractive photometric determination of gallium with 8-quinolinol in layered crystals of bismuth telluride-estimation of the determination limit

A method for determining microgram amounts of gallium in milligram samples of layered monocrystals of the type A(V)(2)B(VI)(3) is described. For the separation of 1-5 mug of gallium(III) from a large excess of bismuth in a single extraction the recommended conditions are pH 3.6-4.2 (acetate buffer, V(aq) 40 ml), an adequate excess of 8-quinolinol for complete extraction and of thiosulphate for masking bismuth. The absorbance of a chloroform extract (V(org) = 10 ml) is measured at 392.5 nm in a 50-mm cell against a blank extract concurrently obtained with a solution of pure Bi(2)Te(3). Reference polycrystalline materials are used to check the precision and accuracy of the method. In routine analysis of layered monocrystals a relative standard deviation of 4-8% is to be expected for about 1 mug of gallium in the extraction system. Estimation of the limit of determination, based on two statistical models, is discussed with respect to the error of the method and the fluctuation of the blank.     

Species-specific isotope dilution analysis of mono-, di,and tri-butyltin compounds in sediment using gas chromatography-inductively coupled plasma mass spectrometry with synthesized 118Sn-enriched butyltins

A species-specific isotope dilution (ID) method is described for the determination of mono-, di, and tri-butyltin compounds in sediment by gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS), where the mixture of 118Sn-enriched butyltin compounds synthesized in our laboratory was used as a spike. A correction method for the mass bias, a quantitative extraction of the butyltins from sediment, and an assay for the concentration of the standard solution for the reverse ID procedure were investigated to achieve a reliable ID analysis. The spike solution was added with tri-propyltin (TPrT), and the butyltins were extracted by mechanical shaking into acetic acid-tropolone-toluene. The extracted butyltins were ethylated with sodium tetraethylborate and measured by GC-ICP-MS. The mass bias correction factor for the butyltins was calculated with the measured area ratio of 120Sn/118Sn of TPrT in each chromatographic run, and the correction was carried out. The mass bias was well corrected with this in-run correction (the standard uncertainties of the corrected 120Sn/118Sn for the butyltins were in the range 0.03-0.45%, typically 0.25%, with triplicate measurement corresponding to 0.02-0.37% mass bias). The extraction efficiency of mono-butyltin (MBT) from sediment was improved by using tropolone-toluene as the solvent. Well-defined standard solutions for the reverse-ID procedure could be obtained by an assay for the purities of the natural abundance butyltin chloride reagents used for preparing the standard solutions. Overall uncertainties associated with the present method were estimated, where the sediment certified reference materials, PACS-2 and BCR 646, were analyzed. The uncertainty arising from the extraction was the main contributor to the overall uncertainties for MBT and di-butyltin (DBT) determinations, while with the case of tri-butyltin (TBT) determination the uncertainties arising from the purity of TBT chloride reagent used for preparing the standard solution was a large contributor to the overall uncertainties although the uncertainty arising from the extraction was also a main contributor. The analytical results of MBT, DBT, and TBT in both reference materials, except for MBT results in PACS-2, were in good agreement with the certified values in each. The result of MBT in PACS-2 (0.677 +/- 0.049 microg g(-1) as tin, mean +/- expanded uncertainty) was significantly higher than the certified value (0.45 +/- 0.05 microg g(-1)), but closely matched with the lately reported values (Rajendran, Tao, Nakazato and Miyazaki, Analyst, 2000, 125, 1757: 0.62 +/- 0.02 microg g(-1); Chiron, Roy, Cottier and Jeannot, J. Chromatogr. A, 2000, 879, 137: 0.634 +/- 0.082 microg g(-1); Alonso, Encinar, Gonzalez and Sanz-Medal, Anal. Bioanal. Chem., 2002, 373, 432: 0.64 +/- 0.04 microg g(-1). The present method is concluded to be reliable for the determination of MBT, DBT, and TBT in sediment.     

固相萃取分离-电感耦合等离子体质谱(ICP-MS)法测定海产品中的无机砷

分别将N-(β氨乙基)-γ-氨丙基三甲氧基硅烷(AEAPTMS)、3-巯丙基三甲氧基硅烷(MPTMS)与四乙氧基硅烷(TEOS)水解共聚,制备氨基\巯基键合的硅胶材料.将此材料作为固相萃取(SPE)小柱的填充材料,建立了固相萃取快速分离富集海产品样品中五价砷As(Ⅴ)和三价砷As(Ⅲ),电感耦合等离子体质谱(ICP-M...     

Comments to EURACHEM/CITAC guide “Measurement uncertainty arising from sampling”

The EURACHEM/CITAC Guide “Measurement uncertainty arising from sampling” deals with the design and analysis of experiments for the evaluation of the sampling and analytical standard deviation when a defined sampling and analytical method is used for the determination of the concentration, expressed as mass fraction (mg/kg), of an analyte in a specified material. The Guide recommends reporting the relative expanded uncertainty and using it directly, i.e. it implicitly assumes that the standard deviation is proportional to the mass fraction even in case the experimental data do not support this assumption. Example A1 (and some of the other examples of the Guide) demonstrates that this can result in extreme levels of underestimation or overestimation of the uncertainty of measurement results. Hence, such recommendations should be avoided!     

Determination of the active metabolite of molsidomine in human plasma by reversed-phase high-performance liquid chromatography

A reversed-phase high-performance liquid chromatographic method, with ultraviolet detection, is proposed for the plasma determination of SIN-1, the active metabolite of molsidomine, which involves propoxycarbonyl derivatization. The internal standard is the ethoxycarbonyl derivative of SIN-1 (i.e. molsidomine). Derivatization and extraction are each performed in one step (2 min) with 70% yield. The nature of a by-product is discussed. The method provides rapid elution (less than 15 min), linearity over the range 0.4-200 ng/ml, day-to-day precision between 2.5 and 11.3% and a limit of determination of 0.5 ng/ml. This method is also suitable for the simultaneous determination of molsidomine and SIN-1. In this case the internal standard is an ethoxycarbonyl derivative of a piperazino-3-sydnonimine, a SIN-1 analogue.