Determination of total taurine in pet foods by liquid chromatography of the dansyl derivative: collaborative study

A liquid chromatographic (LC) method for the determination of total taurine in pet foods was evaluated in a collaborative study. Ten laboratories assayed 6 blind duplicate pairs of wet and dry pet foods. The taurine in the 6 sample pairs ranged from low (170 mg/kg) to high (2250 mg/kg) concentrations as is. Collaborators also assayed a sample of known taurine concentration for familiarization purposes. Samples were hydrolyzed to release bound taurine, which was subsequently converted to the dansyl derivative and quantitated by gradient-elution LC with fluorescence detection. Repeatability relative standard deviations, RSDr, ranged from 3.2 to 10.0%; reproducibility relative standard deviations, RSDR, ranged from 6.1 to 16.1%. The method has been adopted Official First Action status by AOAC INTERNATIONAL.     

Determination of mercury in seafood by flow injection-cold vapor atomic absorption spectrometry after microwave digestion: NMKL interlaboratory study. Nordic Committee on Food Analysis

Ten laboratories participated in an interlaboratory method-performance (collaborative) study of a method for the determination of mercury in foods of marine origin by flow injection-cold vapor atomic absorption spectrometry after wet digestion using a microwave oven technique. The study was preceded by a training round of samples of known identity. The method was tested on a total of 7 seafood products: blue mussel (Mytilus edulis), cod muscle (Gadus morhua), crab (Cancer pagurus), scampi (Nephrops norwegicus), black scabbard fish (Aphnopus carbo), longnose velvet dogfish (Centroscymus crepidater), and Portuguese dogfish (Cenbroscymus coelolepis) with mercury concentrations of 0.14, 0.24, 0.35, 0.59,11.42, 4.2, and 13.2 microg/g, respectively. The materials were presented to the participants in the study as blind duplicates, and the participants were asked to perform single determinations on each sample. Repeatability relative standard deviations (RSDr) for mercury ranged from 2.4 to 14.0%. Reproducibility relative standard deviations (RSDR) ranged from 7.7 to 16.6%. HORRAT values for all samples were <1.0.     

Determination of arsenic in seafood by electrothermal atomic absorption spectrometry after microwave digestion: NMKL collaborative study

Eight laboratories participated in an interlaboratory method performance (collaborative) study of a method for the determination of arsenic in foodstuffs of marine origin by electrothermal atomic absorption spectrometry after wet digestion using a microwave oven technique. The study was preceded by a practice round of familiarization samples. The method was tested on 8 materials (cod roe, krill, blue mussel, saithe, scampi, cod fillet, shrimp, and cod extract) ranging in As content from 2 to 75 mg/kg. The materials were sent to participants in the study as blind duplicates, and the participants were asked to perform single determinations on each sample. Repeatability relative standard deviations (RSDr) for As ranged from 6.8 to 17.4%. Reproducibility relative standard deviations (RSDR) ranged from 7.6 to 24%. The highest RSDR value was found for the sample with the highest concentration of As.     

Determination of arsenic, cadmium, mercury, and lead by inductively coupled plasma/mass spectrometry in foods after pressure digestion: NMKL interlaboratory study

Thirteen laboratories participated in an interlaboratory method performance (collaborative) study on a method for the determination of arsenic, cadmium, mercury, and lead by inductively coupled plasma/mass spectrometry (ICP/MS) after pressure digestion including the microwave heating technique. Prior to the study, the laboratories were able to practice on samples with defined element levels (pretrial test). The method was tested on a total of 7 foodstuffs: carrot puree, fish muscle, mushroom, graham flour, simulated diet, scampi, and mussel powder. The elemental concentrations in mg/kg dry matter (dm) ranged from 0.06-21.4 for As, 0.03-28.3 for Cd, 0.04-0.6 for Hg, and 0.01-2.4 for Pb. The materials used in the study were presented to the participants as blind duplicates, and the participants were asked to perform single determinations on each sample. The repeatability relative standard deviations (RSDr) for As ranged from 3.8 to 24%, for Cd from 2.6 to 6.9%, for Hg from 4.8 to 8.3%, and for Pb from 2.9 to 27%. The reproducibility relative standard deviations (RSDR) for As ranged from 9.0 to 28%, for Cd from 2.8 to 18%, for Hg from 9.9 to 24%, and for Pb from 8.0 to 50%. The HorRat values were less than 1.5 for all test samples, except for the determination of Pb in wheat flour at a level close to the limit of quantitation (0.01 mg/kg dm). The study showed that the ICP/MS method is satisfactory as a standard method for elemental determinations in foodstuffs.     

Determination of polydextrose in foods by ion chromatography: collaborative study

Eight collaborating laboratories assayed 7 blind duplicate pairs of foods for polydextrose content. The 7 test sample pairs ranged from low (2%) to high (95%) levels. The following foods were prepared with polydextrose mixed into the other ingredients and then baked, cooked, or otherwise prepared: milk chocolate candy, iced tea, sugar cookie, grape jelly, soft jellied candy, and powdered drink mix. Collaborators received a polydextrose standard to develop a calibration curve. The method determined polydextrose by ion chromatography, after removal of interfering food components (high molecular weight solubles). Repeatability standard deviations (RSDr) ranged from 3.93 to 9.04%; reproducibility standard deviations (RSDR) ranged from 4.48 to 14.06%. The average recovery was 94%.     

Determination of fluoride in wine by fluoride selective ion electrode, standard addition method: collaborative study

The accuracy, precision, and reproducibility of a rapid method for determination of fluoride in wine, using a fluoride selective ion electrode, were established by a collaborative study involving 12 laboratories, 5 in Europe and 7 in the United States. The laboratories assayed 6 Youden pairs of fluoride-fortified, red and white wine samples with fluoride concentrations ranging from 0.2 to 3.0 mg/L. The relative standard deviations of repeatability ranged from 1.94 to 4.88%; relative standard deviations of reproducibility ranged from 4.15 to 18.40%. HORRAT values ranged from 0.30 to 0.97. The average recovery was 99.97%. Based on the statistical results of this collaborative study, the Study Director recommends that this method be adopted First Action.     

Determination of vegetal proteins in milk powder by sodium dodecyl sulfate-capillary gel electrophoresis: interlaboratory study

An interlaboratory study, with the participation of 8 laboratories, was conducted to evaluate a sodium dodecyl sulfate-capillary gel electrophoresis method for determination of adulteration of milk powder with soy and pea proteins. Calibration standards (0-8%, w/w, soy and pea protein in total protein) and adulterated skim milk powders (0-5%, w/w, soy and pea proteins in total protein) were produced. Vegetal proteins were determined after removal of milk proteins by pretreatment of the samples with tetraborate-EDTA buffer, pH 8.3. Repeatability standard deviations ranged from 9 to 15% and reproducibility standard deviations ranged from 25 to 30% in the samples containing 5% vegetal protein in total protein.     

Determination of semicarbazide in baby food by liquid chromatography/tandem mass spectrometry: interlaboratory validation study

An interlaboratory validation study funded by the European Commission, Directorate General for Health and Consumer Protection (DG SANCO), was conducted to evaluate the effectiveness of a liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for the determination of semicarbazide (SEM) in different types of baby food at a possible future European regulatory limit (10 ng/g). The test portion of the sample was extracted with hydrochloric acid, and the analyte was derivatized with 2-nitrobenzaldehyde, with 1,2-[15N2, 13C] SEM as an internal standard. The extract was neutralized and then purified on a solid-phase extraction cartridge. The SEM was determined by reversed-phase LC with detection by MS/MS. Apple puree, rice pudding, and meat/vegetable meal baby food materials, spiked with SEM at levels of about 3, 10, and 30 ng/g, respectively, were sent to 20 laboratories in 12 different European countries, which submitted results from 17 participants. Recoveries ranged from 88.8 to 106.1%. Based on results for spiked samples (blind pairs at 3 levels), the relative standard deviations for repeatability (RSDr) ranged from 4.2 to 6.9% and the relative standard deviations for reproducibility (RSDR) ranged from 16.6 to 24.3%. The method showed acceptable within- and between-laboratory precision for all 3 matrixes, as evidenced by HorRat values, at the target levels for the determination of SEM.     

Determination of naringin and neohesperidin in orange juice by liquid chromatography with UV detection to detect the presence of grapefruit juice: Collaborative Study

Fifteen collaborating laboratories were sent 9 samples of citrus juice mixtures as blind duplicates for determination of naringin and neohesperidin by liquid chromatography. Two sample pairs were 100% orange juice and did not contain any naringin or neohesperidin. The remaining 7 sample pairs contained naringin at levels ranging from 3.9 to 46.5 ppm and neohesperidin at levels ranging from 0.14 to 35.6 ppm. Five sample pairs consisted of orange juice mixtures containing 1, 3, and 5% grapefruit juice; 5% sour orange; and 5% K-Early citrus variety. Two sample pairs were orange juice spiked with naringin, neohesperidin, sodium benzoate, and potassium sorbate. Data were received from 13 laboratories. Data from 1 collaborator were eliminated because the method protocol was not followed. Neohesperidin values from another laboratory were also not used because of problems with a coeluting component. Repeatability relative standard deviations ranged from 2.95 to 15.23% for naringin and from 3.00 to 11.74% for neohesperidin. Reproducibility relative standard deviations ranged from 11.34 to 31.94% for naringin and from 10.45 to 26.17% for neohesperidin. The method is reliable for detecting the presence of grapefruit juice in orange juice as indicated by a finding of > or =10 ppm naringin and < or =2 ppm neohesperidin. The method was adopted First Action by AOAC INTERNATIONAL.     

Determination of coenzyme Q10 content in raw materials and dietary supplements by high-performance liquid chromatography-UV: collaborative study

An international collaborative study was conducted of a high-performance liquid chromatographic (HPLC)-UV method for the determination of coenzyme Q10 (CoQ10, ubidecarenone) in raw materials and dietary supplements. Ten collaborating laboratories determined the total CoQ10 content in 8 blind duplicate samples. Sample materials included CoQ10 raw material and 4 finished product dietary supplements representing softgels, hardshell gelatin capsules, and chewable wafers. In addition, collaborating laboratories received a negative control and negative control spiked with CoQ10 at low and high levels to determine recovery. Materials were extracted with an acetonitrile-tetrahydrofuran-water mixture. Ferric chloride was added to the test solutions to ensure all CoQ10 was in the oxidized form. The HPLC analyses were performed on a C18 column using UV detection at 275 nm. Repeatability relative standard deviations (RSDr) ranged from 0.94 to 5.05%. Reproducibility relative standard deviations (RSDR) ranged from 3.08 to 17.1%, with HorRat values ranging from 1.26 to 5.17. Recoveries ranged from 74.0 to 115%. Based on these results, the method is recommended for Official First Action for determination of CoQ10 in raw materials and dietary supplement finished products containing CoQ10 at a concentration of >100 mg CoQ10/g test material.     

Determination of docosahexaenoic acid and n-3 fatty acids in refined fish oils by 1H-NMR spectroscopy: IUPAC interlaboratory study

A high-resolution proton nuclear magnetic resonance (NMR) method for determining the concentration (mg/g) of docosahexaenoic acid (DHA), the molar proportion (mol%) of DHA, and the molar proportion of total n-3 fatty acids in fish oils was validated by an IUPAC interlaboratory study (the Commission VI-6 on Oils, Fats, and Derivatives WG 3/98). Thirteen laboratories from 5 countries tested 6 pairs of blind duplicate fish oils: a refined tuna oil, 2 extracted tuna oils, an extracted bonito oil, an extracted salmon oil, and an extracted sardine oil ranging from 9 to 30 mol% DHA and from 20 to 35 mol% n-3 fatty acids. Before 1 D-proton NMR measurements with 300-500 MHz instruments, oil samples were weighed and diluted with deuterochloroform solution containing ethylene glycol dimethyl ether as internal standard. To achieve precise performance, a detailed procedure for signal area measurement was described in the protocol, and all participants were instructed about the critical importance of following the protocol. Statistical performances with invalid and outlier data removed were as follows: repeatability relative standard deviations (RSDr) ranged from 0.91 to 2.62% and reproducibility relative standard deviation (RSDR) ranged from 1.73 to 4.27% for DHA concentration (mg/g); RSDr ranged from 0.39 to 2.06%, and RSDR ranged from 0.59 to 3.46% for mol% DHA; RSDr ranged from 0.23 to 0.90% and RSDR ranged from 0.85 to 2.01 % for mol% total n-3 fatty acids. The method is expected to be recommended by IUPAC.     

Trace level determination of acrylamide in cereal-based foods by gas chromatography-mass spectrometry

A quantitative method has been developed for the determination of trace levels (<50 microg/kg) of acrylamide in cereal-based foods. The method is based on extraction of acrylamide with water, acidification and purification with Carrez I and II solutions, followed by bromination of the acrylamide double bond. The reaction product (2,3-dibromopropionamide) is extracted with ethyl acetate/hexane (4:1, v/v), dried over sodium sulfate, and cleaned up through a Florisil column. The derivative is then converted to 2-bromopropenamide by dehydrobromination with triethylamine and analyzed by gas chromatography coupled to mass spectrometry (GC-MS), employing (13C3)acrylamide as internal standard. In-house validation data for commercial and experimental cereal products showed good precision of the method, with repeatability and intermediate reproducibility relative standard deviations below 10%. The limit of detection and limit of quantitation are estimated at 2 and 5 microg/kg, respectively, and recoveries of acrylamide from samples spiked at levels of 5-500 microg/kg ranged between 93 and 104% after correction of analyte loss by the internal standard. Finally, a comparative test organized with two independent laboratories provided additional confidence in the good performance of the method, particularly at very low concentration levels.     

Liquid chromatographic determination of lysine, methionine, and threonine in pure amino acids (feed grade) and premixes: collaborative study

A total of 17 laboratories (including one author's laboratory) participated in a collaborative study for determination of lysine, methionine, and threonine in trade products or concentrated amino acid premixes. Thirteen samples, 4 pure amino acids and 6 premixes, including 3 Youden matched pairs, were analyzed. The applied liquid chromatographic (LC) method using cation-exchange resin and post-column derivatization with ninhydrin or o-phthaldialdehyde was shown to be accurate and specific for the analytes. Titration procedures, normally used for the assay of pure amino acids, are unspecific and the accuracy of the results can be affected by impurities. Repeatability relative standard deviations, RSDr, ranged from 0.84 to 1.17% for pure amino acids and from 0.50 to 1.68% for premixes; reproducibility relative standard deviations RSDR, ranged from 1.52 to 2.31% for pure amino acids and from 1.48 to 2.59% for premixes. Recoveries were between 97.5 and 102.8% of the expected amino acid assays. The method has been adopted Official First Action status by AOAC INTERNATIONAL.     

Determination of clopidol residues in chicken tissues by liquid chromatography: collaborative study

Eighteen laboratories participated in a collaborative study on the determination of clopidol residues in chicken muscle tissues by liquid chromatography. Of these, results from 16 laboratories which rigorously followed the method were subjected to statistical analysis. The method performance was assessed by all participants using 14 samples of chicken muscle fortified at concentrations ranging from 0.1 to 5.0 mg/kg. In addition, 9 participants each reported results for 6 clopidol-incurred samples in chicken muscle. Test portions were extracted with acetonitrile, and the extracts were purified with alumina and anion exchange resin solid-phase extraction cartridges in sequence. Clopidol was separated by reversed-phase liquid chromatography and quantified at 270 nm. Average recoveries ranged from 81.8 to 85.4%, reproducibility relative standard deviation (RSDR) ranged from 11.9 to 22.6%, and repeatability relative standard deviation (RSDr) ranged from 9.9 to 15.1%. For clopidol-incurred samples at concentrations of 0.100-0.687 mg/kg, the mean determination value range was 0.099-0.659 mg/kg; RSDR was 12.6-19.8%, RSDr was 3.1-8.5%; and HORRAT values were 0.7-1.1. The accuracy and precision of the method are in conformity with the requirements specified by AOAC INTERNATIONAL. The method was adopted Official First Action in April 2003.     

Determination of total soy isoflavones in dietary supplements, supplement ingredients, and soy foods by high-performance liquid chromatography with ultraviolet detection: collaborative study

An interlaboratory study was conducted to evaluate a method for determining total soy isoflavones in dietary supplements, dietary supplement ingredients, and soy foods. Isoflavones were extracted using aqueous acetonitrile containing a small amount of dimethylsulfoxide (DMSO) and all 12 of the naturally occuring isoflavones in soy were determined by high-performance liquid chromatography (HPLC) with UV detection using apigenin as an internal standard. Fifteen samples (6 pairs of blind duplicates plus 3 additional samples) of soy isoflavone ingredients, soy isoflavone dietary supplements, soy flour, and soy protein products were successfully analyzed by 13 collaborating laboratories in 6 countries. For repeatability, the relative standard deviations (RSDr) ranged from 1.07 for samples containing over 400 mglg total isoflavones to 3.31 for samples containing 0.87 mg/g total isoflavones, and for reproducibility the RSDR values ranged from 2.29 for samples containing over 400 mg/g total isoflavones to 9.36 for samples containing 0.87 mg/g total isoflavones. HorRat values ranged from 1.00 to 1.62 for all samples containing at least 0.8 mg/g total isoflavones. One sample, containing very low total isoflavones (< 0.05 mg/g), gave RSDR values of 175 and a HorRat value of 17.6. This sample was deemed to be below the usable range of the method. The method provides accurate and precise results for analysis of soy isoflavones in dietary supplements and soy foods.     

固相分散萃取与气相色谱-负化学离子源质谱联用法测定食品中三唑醇的残留量

建立了食品中三唑醇残留量的固相分散萃取-气相色谱-负化学离子源质谱联用检测方法。样品中三唑醇残留物由正己烷饱和的乙腈(含1%冰醋酸)提取,加入无水硫酸镁与无水醋酸钠振荡促使提取液分层后进行固相分散萃取净化,用气相色谱-负化学离子源质谱法进行测定与确证,外标法定量。方法具有良好的选择性和抗干扰能力,其检出限和定量限分别为0.001 mg/kg和0.003 mg/kg;线性范围为0.050～0.750 mg/L,相关系数为0.9947;在0.005,0.010,0.020 mg/kg共3个添加水平下的平均回收率为70%～110%,相对标准偏差不大于12.0%。该方法适合于多种食品中三唑醇残留量的确证分析。     

Evaluation of analyte stability and method ruggedness in the determination of streptomycin residues in honey by liquid chromatography with post-column derivatization

This study demonstrated that streptomycin in honey is quite stable, and the results showed no obvious differences for 3 samples containing incurred analyte during continuous testing for 4 months. Fifteen laboratories evaluated method performance at 4 fortification levels ranging from 0.010 to 0.100 mg/kg; the recoveries ranged from 73.7 to 78.5%, the reproducibility relative standard deviations ranged from 5.76 to 15.85%, and the repeatability relative standard deviations ranged from 1.64 to 3.80%. In 1999-2002, the method was used to determine streptomycin residues in 5106 lots of honey samples from >20 provinces all over China. All of the honey samples were found to be in conformity with the requirements of customs clearance for exports to Europe, the United States, and Japan. The continuous 4-year quality analysis also found that C18 solid-phase extraction cartridges should be standardized to ensure that the analytical results are accurate when different lots of cartridges are used.     

高效液相色谱法测定化妆品中氯噻酮和吩噻嗪

建立了反相高效液相色谱法测定化妆品中氯噻酮和吩噻嗪的分析方法。化妆品中氯噻酮和吩噻嗪用丙酮超声提取,采用Kromasil C18色谱柱(5μm,250 mm×4.6 mm i.d.),以30 mmol/L NaH2PO4缓冲液(pH 5.6)和甲醇为流动相进行梯度洗脱,得到了理想的分离效果。氯噻酮和吩噻嗪在0.2~100 mg/L范围内,质量浓度与其峰面积呈良好的线性关系。在低、中、高3个添加水平下,氯噻酮的平均回收率为94.8%~104.1%,RSD为0.7%~4.4%,吩噻嗪的平均回收率为92.5%~103.1%,RSD为1.0%~6.9%。方法可用于化妆品中氯噻酮和吩噻嗪的检测。     

QuEChERS-超高效液相色谱-串联质谱法测定动物源食品中痕量五氯酚及其钠盐

采用改良的QuEChERS-超高效液相色谱-串联质谱（UPLC-MS/MS）技术,建立了动物源食品中痕量五氯酚及其钠盐的测定方法。样品中五氯酚钠在酸性条件下转化为五氯酚,采用1%（v/v）乙酸乙腈超声提取2次,提取液浓缩后分散固相萃取净化,以回收率及基质效应为考察指标,对吸附剂进行了优化。采用Waters Acquity UPLC HSS T3色谱柱梯度洗脱分离,在电喷雾电离（ESI）源、负离子模式和多反应监测模式下检测,基质匹配外标法定量。在1.0、2.0、10.0 μg/kg添加水平下6种基质（猪肉、猪肝、鸡肉、鱼肉、牛奶、鸡蛋）中五氯酚的加标回收率为73.2%~108.4%,相对标准偏差为4.0%~14.8%;定量限（S/N>10）为1.0 μg/kg。该方法简便、灵敏、准确、环保,适用于动物源食品中痕量五氯酚及其钠盐残留的定性定量分析。     

Microbiological assay-trienzyme procedure for total folates in cereals and cereal foods: collaborative study

In 1996, U.S. Food and Drug Administration regulations mandated the fortification of enriched cereal-grain products with folic acid, thereby emphasizing the need for validated methods for total folates in foods, particularly cereal products. The AOAC Official Methods (944.12, 960.46) currently used for the analysis of folate in foods for compliance purposes are microbiological methods. When the fortification regulations were finalized, no Official AOAC or Approved AACC methods for folate in cereal-grain products were in place. The AOAC Official Method (992.05) for folic acid in infant formula does not incorporate important improvements in the extraction procedure and was not considered suitable for the analysis of folates in foods in general. A microbiological assay protocol using a trienzyme extraction procedure was prepared and submitted for comments to 40 laboratories with recognized experience in folate analysis. On the basis of comments, the method was revised to have the conjugase (gamma-glutamyl-carboxy-peptidase) treatment follow a protease treatment, to include the use of cryoprotected inoculum, and to include the spectroscopic standardization of the standard and optional use of microtiter plates. Thirteen laboratories participated in a collaborative study of 10 required and 10 optional cereal-grain products, including flour, bread, cookies, baking mixes, and ready-to-eat breakfast cereals. The majority of the participating laboratories performed the assay by the standard test tube method; others used the microtiter plate modification for endpoint quantitation with equal success. For the required products, the relative standard deviation between laboratories (RSD(R)) ranged from 7.4 to 21.6% for 8 fortified (or enriched) products compared with expected (Horwitz equation-based) values of 11-20%. RSD(R) values were higher (22.7-52.9%) for 2 unfortified cereal-grain products. For the optional products, the RSD(R) ranged from 1.8 to 11.2% for 8 fortified products. RSD(R) values were higher (27.9-28.7%) for 2 unfortified cereal-grain products. Based on the results of the collaborative study, the microbiological assay with trienzyme extraction is recommended for adoption as Official First Action.