Development of melamine certified reference material in milk using two different isotope dilution mass spectrometry techniques

A new certified reference material (CRM) of melamine in milk GLHK-11-02 was developed aiming to address the great demand from the testing community after the melamine crises. The material was prepared by adding an appropriate quantity of melamine into the skimmed milk samples and the final product was in the form of fine lyophilized powder. Characterization of the material relied on two newly developed gravimetric isotope dilution mass spectrometry (IDMS) methods, one using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and another gas chromatography-mass spectrometry (GC-MS). Experimental parameters with crucial effects on the performance of the two IDMS methods were thoroughly investigated. These included purity of standard used, equilibration time of isotopes, efficiency of extraction methods as well as possible interferences from the matrix and melamine analogues. Precision was found to be excellent with a coefficient of variation of 2.5% for the LC-IDMS/MS (n=46) and 1.9% for the GC-IDMS (n=30) respectively. Using one-tail Student's t-test at 95% confidence interval, analytical data sets generated from the two methods were found to exhibit no significant difference. Measurement accuracy of the methods was further verified through an Asia Pacific Metrology Program (APMP) pilot study. Analytical results of the present LC-IDMS/MS for the two milk test samples at the concentration level of about 0.45 and 3.5 mg kg(-1) were proven to be very good. There were excellent overlaps between our results and the assigned reference values, and the absolute deviation was less than 3.2%. Both the LC-IDMS/MS and GC-IDMS methods were shown to be sufficiently reliable and accurate for certification of the melamine CRM. Certified value of melamine in dry mass fraction in GLHK-11-02 was 1.14 mg kg(-1). Expanded uncertainty due to sample inhomogeneity, long term and short term stability and variability in the characterization procedure was at 7.1% or 0.08 mg kg(-1). The CRM is primarily used to provide a complete method validation for and to improve the technical competence of melamine analysis to food and chemical testing laboratories.     

Purity assessment for 17��-estradiol

Purity assessment for high-purity organic substances is regarded as one of the core competences of national metrology institutes. For this reason, Consultative Committee for Amount of Substance??Metrology in Chemistry (CCQM) regularly organized intercomparison studies to compare and demonstrate the degree of equivalence of national measurement capabilities for purity determination. This paper reports the method development work for the participation in a recent CCQM key comparison on purity assessment for estradiol. An indirect consecutive estimation approach was adopted to determine the purity of the estradiol sample, i.e., through the identification and quantification of all possible impurities present in the sample. In the course of assessment, a variety of analytical techniques were applied. The most challenging part was to identify and estimate the amount of unknown organic-related substance present in the testing material. For the moisture determination, a gas chromatography with thermal conductivity detection (GC?CTCD) method was employed to supplement the results obtained using coulometric Karl Fischer titration technique. Inorganic impurities and volatile organic compounds residual were analyzed using inductively coupled plasma mass spectrometry (ICP?CMS) and gas chromatography?Cmass spectrometry (GC?CMS) techniques, respectively, and their contributions were found to be comparatively insignificant.     

A bilateral study for the establishment of comparability in the measurement of ethanol in bioethanol fuel using isotope dilution mass spectrometry

A bilateral comparative study between two metrology institutes was conducted for the determination of ethanol in bioethanol fuel by isotope dilution mass spectrometry. Measurement procedures were independently developed by the Health Sciences Authority (Singapore) and the National Institute of Metrology (People??s Republic of China). The methods used included headspace gas chromatography?Chigh-resolution mass spectrometry, headspace gas chromatography?Cmass spectrometry (GC-MS) and direct injection to GC-MS. An investigation of all potential sources of uncertainty, including a component of uncertainty due to the effect of using different instruments such as gas chromatography?Cflame ionization detector method, commonly adopted for the analysis of organic volatiles, was carried out. The results of the analyses are consistent within the associated measurement uncertainty of each laboratory, reported at approximately 95% confidence level.     

Providing a traceable assigned value in a proficiency testing programme on the determination of benzoic acid in orange juice

A proficiency testing (PT) programme on the determination of benzoic acid in orange juice was organised by the Chemical Metrology Laboratory, Health Sciences Authority, Singapore, for the local food testing laboratories. The PT programme used a metrologically traceable assigned value determined by isotope dilution mass spectrometry to assess the performance of the participating laboratories. This paper discusses the reasons and approach to applying metrological principles to determine the assigned value of a PT programme. The procedure undertaken by the Laboratory to prepare a batch of PT sample, conduct homogeneity and stability testings, as well as value assignment, is presented. The discussions also include the estimation of the measurement uncertainties arising from the characterisation, testing for homogeneity and testing for stability of the PT sample. The Coordinator of the PT programme used the assigned value and its associated measurement uncertainty, together with those of the participating laboratories to assess their performances. Statistical tools applied in the performance evaluations are also presented.     

Development of metrology for pH measurement in Thailand

It has not been long that metrology is well accepted as an important part in analytical chemistry since it helps the chemists to receive the best measurement and accurate results with traceability. The National Institute of Metrology Thailand (NIMT), which is a public agency under the supervision of the Ministry of Science and Technology, not only focuses on physical standards but also provides and maintains standards in chemical field. pH measurement is one of the most widely used in the laboratories including industries and medical area in Thailand. The chemical laboratory starts working on the project with the objective of disseminating an accurate result in routine pH measurement. In 2002, the laboratory provided a service in calibration of pH meter and organized the first local interlaboratory comparison program (NIMT–C-ILC-1: pH buffer) in pH measurement. There were three buffer solution samples in the range of acid, neutral, and base. A total of 44 laboratories participated in this program. The NIMT chemical laboratory also participated in the proficiency testing program that was conducted by PSB Corporation Testing Group in Singapore. In 2003, NIMT started research in preparation of secondary buffers by using highly accurate pH meters with glass electrode systems. The laboratory produced three secondary buffers, which were pH 4.01, 6.86, and 9.18 with uncertainty 0.020 pH at 25°C. The competence of the laboratory was shown by the measurement results of the pilot study (APMP.QM-P06), which was organized by the APMP electrochemical analysis working group (EAWG/TCQM) in 2005. The title of this study was “pH determination of two phosphate buffers by Harned cell method and glass electrode method”. NIMT aims to achieve for establishment of the primary method for pH measurement in the near future. Presented at -- “BERM-10” -- April 2006, Charleston, SC, USA     

The role of metrology in chemistry in the upholding of public health and food safety in Hong Kong

The Government Laboratory has been involved in the provision of analytical and advisory services since its formal establishment in 1913 in support of the needs of the community and the commitments of the Government of Hong Kong Special Administrative Region, China. One of the earliest areas of work involves the testing of food samples for maintenance of public health and food safety. Remarkable advances in technology in recent years coupled with the introduction of new policies and regulations, the launching of new international standards and requirements have all contributed to significant and ever-rising demand of accurate, specific, comparable and traceable measurements using the latest technologies for a wide variety of additives, contaminants, residues and genetically modified ingredients in food.Metrology, the science of measurement, has always played a key role in the development and validation of analytical methodologies in the Government Laboratory for the realization of its measurements to the highest level of accuracies and traceability to internationally recognized standards. Besides the application of the latest analytical technologies such as isotope dilution mass spectrometry, tandem mass spectrometry, real-time polymerase chain reactions, etc., the Analytical and Advisory Services Division of the Laboratory develops a quality assurance system in full compliance with the requirements of ISO/IEC 17025 and endeavours to ensure that every analytical methods are validated with the best applicable means and are fit for the intended purposes. In this presentation, the role and application of metrology in chemistry in the measurements pertaining to public health and food safety work undertaken by the Government Laboratory are discussed.Presented at International Symposium on Metrology in Chemistry, 2004 Beijing, China.     

Development of a candidate certified reference material of cypermethrin in green tea

This paper presents the preparation of a candidate certified reference material (CRM) of cypermethrin in green tea, GLHK-11-01a according to the requirements of ISO Guide 34 and 35. Certification of the material was performed using a newly developed isotope dilution mass spectrometry (IDMS) approach, with gas chromatography high resolution mass spectrometry (GC–HRMS) and gas chromatography–tandem mass spectrometry (GC–MS/MS). Statistical analysis (one-way ANOVA) showed excellent agreement of the analytical data sets generated from the two mass spectrometric detections. The characterization methods have also been satisfactorily applied in an Asia-Pacific Metrology Program (APMP) interlaboratory comparison study. Both the GC–HRIDMS and GC–IDMS/MS methods proved to be sufficiently reliable and accurate for certification purpose. The certified value of cypermethrin in dry mass fraction was 148 μg kg⁻¹ and the associated expanded uncertainty was 14 μg kg⁻¹. The uncertainty budget was evaluated from sample in homogeneity, long-term and short-term stability and variability in the characterization procedure. GLHK-11-01a is primarily developed to support the local and wider testing community on need basis in quality assurance work and in seeking accreditation.     

衍生化-离子阱气相色谱质谱联用检测乳粉中三聚氰胺时不同质谱检测方法研究

利用N,O-双三甲基硅基三氟乙酰胺(BSTFA)和三甲基氯硅烷(TMCS)衍生化试剂对乳粉中三聚氰胺进行衍生化处理,利用离子阱气相色谱质谱联用仪,建立了全扫描、选择离子监测、二级质谱3种测定三聚氰胺的质谱方法.选择离子监测以三聚氰胺衍生物的特征离子m/z342,327,171,99为定性离子,以m/z327为定量离子;全扫描法二级质谱特征峰为定性依据,以特征离子m/z327为定量离子;二级质谱法以衍生物二级质谱m/z285,171,213为定性离子,以m/z 285为定量离子.3种方法的线性范围为0.05～2.0 mg/L,线性相关系数分别为0.9986、0.9990、0.9988;检测限分别为0.005、0.002、0.003 mg/kg,RSD分别为6.3%、5.7%、6.1%(n=6),方法的回收率为84%～105%.3种不同质谱检测方法应用到乳粉的检测中效果良好,均能够满足乳粉中三聚氰胺的检测要求.     

亲水作用色谱-串联质谱法同时测定液态奶中三聚氰酸和三聚氰胺

建立了亲水作用色谱-串联质谱同时测定液态奶中三聚氰酸和三聚氰胺的方法。液态奶样品经体积分数2.5%甲酸溶液提取、离心后乙腈稀释,亲水作用色谱柱分离,电喷雾串联四极杆质谱检测器检测,分别在负、正离子模式下测定三聚氰酸和三聚氰胺。三聚氰酸和三聚氰胺分别在0.5～100μg/L、0.1～50μg/L范围内线性关系良好。在0.25～15mg/kg、0.1～7.5mg/kg添加水平范围内,三聚氰酸平均回收率为84.5%～98.0%(RSD为2.1%～6.1%),三聚氰胺平均回收率为85.5%～88.9%(RSD为3.2～5.8%)。三聚氰酸、三聚氰胺定量限分别为0.25mg/kg、0.1mg/kg。     

Modeling of separations by closed-loop steady-state recycling chromatography of a racemic pharmaceutical intermediate

The following review describes the development of mass spectrometry off-line and on-line coupled with liquid chromatography to the analysis of food proteins. It includes the significant results recently obtained in the field of milk, egg and cereal proteins. This paper also outlines the research carried out in the area of food protein hydrolysates, which are important components in foodstuffs due to their functional properties. Liquid chromatography and mass spectrometry have been particularly used for the characterization of food peptides and especially in dairy products.     

International comparability of determination of mass fractions of chromium, copper, iron, manganese and zinc in aluminium alloy: Comité Consultatif pour la Quantité de Matière key comparison K42

The degree of equivalence within the participating national metrology institutes for the measurement results of the mass fractions of the analytes Cr, Cu, Fe, Mn and Zn in an aluminium alloy was assessed. This interlaboratory comité consultatif pour la quantité de matière key comparison (CCQM-K42) was organised as an activity of the Inorganic Analytical Working Group of CCQM. In total seven laboratories participated, six of them for all analytes. Measurands were the mass fractions of the analytes in a range of 0.05 and 0.2%. As an outcome the consistency of the results for all elements investigated was acceptable, hence satisfactory comparability was established. An aluminium based certified reference material—undisclosed to the analysts which one it was—was used as test sample. For the purpose of this study homogeneity was tested at BAM. Each laboratory was free to choose any analytical method they wanted to use for the analysis. Consequently various methods of measurement were employed: instrumental neutron activation analysis, X-ray fluorescence spectrometry (XRF) using fused cast-bead method combined with reconstitution technique, inductively coupled plasma optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry. Metrological traceability of the measurement results to the SI unit had to be demonstrated. Therefore, methods such as spark OES or XRF (without fused cast-bead technique)—both of them being most important methods for the analysis of metals and alloys in industrial laboratories—could not be used in the frame of the key comparison.     

表面解吸常压化学电离质谱法直接测定奶粉中三聚氰胺

应用表面解吸常压化学电离(SDAPCI)质谱法,在无需样品预处理的情况下,直接测定了奶粉中三聚氰胺,并用串联质谱法对测定结果进行了鉴定.采用手动进样,单个样品测定时间少于0.5 min,回收率为86.7%～112.8%;相对标准偏差(RSD)为4.3%～10.3%;对奶粉中三聚氰胺的检出限为8.8 μg/kg.方法适用于批量样品的快速半定量检测.     

Analysis of melamine in milk powder by using a magnetic molecularly imprinted polymer based on carbon nanotubes with ultra high performance liquid chromatography and tandem mass spectrometry

A new magnetic molecularly imprinted polymer was coupled with ultra high performance liquid chromatography and tandem mass spectrometry for the selective determination of melamine in milk powder. The magnetic molecularly imprinted polymer has been prepared by using carbon nanotubes as the matrix, Fe₃O₄ particles as the magnetic ingredient, melamine as the template molecule, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross‐linker and polyvinylpyrrolidone as the dispersant. The polymer was characterized with scanning electron microscopy, Fourier transform infrared spectroscopy and a physical property measurement system. The isothermal adsorption, kinetics adsorption, and selectivity were studied to evaluate the rebinding properties of the magnetic molecularly imprinted polymer. Various parameters affecting the extraction efficiency such as the amount of polymer, extraction time, and eluting solution were evaluated. The limit of detection was 0.00075 mg/kg. The relative standard deviations of the intraday and interday precision are 0.4–2.7 and 2.3–5.1%, respectively. The proposed method was successfully applied to determine melamine in different milk powder samples from different provenances, and satisfactory recoveries of 89.0–95.6% were obtained. This method has great significance for quality control and is simple and suitable for the rapid determination of melamine in milk powder.     

One way of disseminating reference values with demonstrated traceability and demonstrated uncertainty to field laboratories: IMEP

An operational interlaboratory comparison programme is described which disseminates SI-traceable reference values to laboratories worldwide. These reference values have an uncertainty and traceability that is demonstrated at the highest metrological level. Participating laboratories can use these values to establish the degree of equivalence of their measurement results and can use this to support their measurement capability claims, e.g. towards third parties. The programme has been run by the Institute for Reference Materials and Measurements (IRMM) since 1988, in the first phase as an awareness programme. Currently, IRMM is focusing its efforts on educational aspects of metrology via a collaboration with the European Co-operation for Accreditation, national metrological institutes (NMIs) and interested academic networks. The viewgraphs used are presented in the “Electronic Supplementary Material” of this ACQUAL issue.     

An international assessment of the metrological equivalence of higher-order measurement services for creatinine in serum

The Consultative committee for amount of substance-metrology in chemistry (CCQM)-K80 Key Comparison directly assessed the equivalence of many of the world’s higher-order value-assigned materials (HOVAMs) for creatinine in human serum. This 2009 international study compared the certified values and uncertainties of the materials using measurements made under repeatability conditions. The study evaluated 17 materials submitted by 6 national metrology institutes (NMIs). The creatinine quantity in these materials ranged from 3 mg/kg to 57 mg/kg (about 0.3 mg/dL to 6 mg/dL or 30 nmol/L to 500 nmol/L). All materials were stored and prepared according the specifications provided by the participating NMIs. Samples were processed and analyzed under repeatability conditions by one analyst using isotope-dilution liquid chromatography–mass spectrometry in two measurement campaigns. The certified values and repeatability measurements were compared using uncertainty-weighted generalized distance regression. The instrumental repeatability relative standard deviation was 1.2%. The measurement design required assessment of within-unit and between-campaign variability in addition to measurement repeatability. At a 95% level of confidence, the certified values for all 17 materials agreed to within their assigned uncertainties. CCQM-K80 demonstrated the metrological equivalence of the currently available HOVAMs for creatinine in human serum and of the creatinine measurement services provided by the participating NMIs.     

Determination of melamine in milk powder using gas chromatography-high-resolution isotope dilution mass spectrometry

A GC-high-resolution isotope dilution MS (IDMS) method for the quantification of melamine in milk powder is described. The developed technique is compared to the LC-IDMS/MS technique, typically used for the determination of melamine in various matrices. The accuracy of the GC-high-resolution IDMS method was demonstrated when a small degree of equivalence was obtained in a regional comparative study involving the determination of melamine in milk powder.     

Regional cooperation in proficiency testing: strategy planning and practical experiences in Western Balkan countries

The article describes the project of regional cooperation in proficiency testing within CARDS 2006 (assistance programme to the Western Balkans), which was coordinated by European Committee for Standardization, European Commission and European Free Trade Association and conducted by the University of Ljubljana, Faculty of Electrical Engineering, Laboratory of Metrology and Quality. The later is the holder of the national standard for thermodynamic temperature as well as an accredited proficiency testing provider and also accredited as a calibration, testing and inspection laboratory. It is also responsible for graduate study programme Quality Engineering. Proficiency testing was considered as a core activity of the entire project, but additionally as a very appropriate platform for knowledge transfer of EU technical legislation in selected sectors, metrology, testing and quality assurance in general. The project had a high added value for participating laboratories in countries of Western Balkans, because it required an active role of all participating laboratories, assured participation of staff from national metrology institutions, all national accreditation bodies, and was supported by national quality infrastructures, such as standardization, governmental institutions etc. in the entire Western Balkans region. The activities stimulated progress in the area of conformity assessment, added knowledge to the implementation of technical directives and development of the technical part of national legislation and therefore facilitated the process toward the accession to the European Union. The main objective was therefore to organize proficiency testing in those sectors (construction, consumer protection and environment) that were vital in the pre-accession process of countries seeking full implementation of EU technical legislation.     

气相色谱-串联质谱法测定食品中的三聚氰胺

建立了使用气相色谱-串联质谱(GC-MS/MS)测定食品中三聚氰胺含量的分析方法。利用三氯乙酸超声萃取样品中的三聚氰胺,经乙酸锌溶液沉淀蛋白质后,将提取液离心、过滤、净化、衍生后采用GC-MS/MS的多反应监测模式（MRM）进行检测。方法的重现性良好,6次重复测定的峰面积的相对标准偏差小于9%;最低定量检测限（S/N=10）为1 μg/kg,在0.1~100 μg/L范围内具有良好的线性关系。应用所建立的方法测定了奶粉、奶糖、含乳饮料、饼干等食品中的三聚氰胺含量,为三聚氰胺滥用的检测和判断提供了方法。     

Verification of cheeses authenticity by mass spectrometry

Cheeses are a group of fermented dairy products that are produced all over the world in various forms and flavours. Milk, especially sheep or goat milk, is still regarded as an expensive raw material in the world, which makes milk and milk products highly attractive as a fraud target. Most often, such fraud includes partial or complete substitution with cheaper sorts of milk (e.g. bovine milk). The aim of this work was to verify the authenticity of 27 cheeses commonly emerging on the Czech food market. The cheeses were distinguished on the basis of milk animal species origin. For this purpose, two mass spectrometry techniques were used: matrix‐assisted laser desorption/ionization with time of flight mass spectrometry together with principal component analysis method and liquid chromatography coupled with electrospray ionization and quadrupole time‐of‐flight mass spectrometry. The results were a partial success, because the cheeses could only be partially distinguished with the first mass spectrometry technique probably because of the influence of some protein additive materials in cheeses. The second technique allowed for collecting higher quality results and thus appears to be highly suitable for the research task.     

Challenges and trends in the determination of selected chemical contaminants and allergens in food

This article covers challenges and trends in the determination of some major food chemical contaminants and allergens, which-among others-are being monitored by Health Canada's Food Directorate and for which background levels in food and human exposure are being analyzed and calculated. Eleven different contaminants/contaminant groups and allergens have been selected for detailed discussion in this paper. They occur in foods as a result of: use as a food additive or ingredient; processing-induced reactions; food packaging migration; deliberate adulteration; and/or presence as a chemical contaminant or natural toxin in the environment. Examples include acrylamide as a food-processing-induced contaminant, bisphenol A as a food packaging-derived chemical, melamine and related compounds as food adulterants and persistent organic pollutants, and perchlorate as an environmental contaminant. Ochratoxin A, fumonisins, and paralytic shellfish poisoning toxins are examples of naturally occurring toxins whereas sulfites, peanuts, and milk exemplify common allergenic food additives/ingredients. To deal with the increasing number of sample matrices and analytes of interest, two analytical approaches have become increasingly prevalent. The first has been the development of rapid screening methods for a variety of analytes based on immunochemical techniques, utilizing ELISA or surface plasmon resonance technology. The second is the development of highly sophisticated multi-analyte methods based on liquid chromatography coupled with multiple-stage mass spectrometry for identification and simultaneous quantification of a wide range of contaminants, often with much less requirement for tedious cleanup procedures. Whereas rapid screening methods enable testing of large numbers of samples, the multi analyte mass spectrometric methods enable full quantification with confirmation of the analytes of interest. Both approaches are useful when gathering surveillance data to determine occurrence and background levels of both recognized and newly identified contaminants in foods in order to estimate human daily intake for health risk assessment.