Quality assurance for the analytical data of micro elements in food

The micro element content of food is an important quality index due to the action of these elements on human health. In this article, we discuss how to ensure the reliability of analytical data on micro elements in order to truly represent the condition of food. Sampling, treatment of the analytical sample, selection of the analytical method, standard solution, and certified reference material, blank test, calibration of the instrument and equipment, application of the quality control chart, assessment of the final analytical result, and quality assurance system are briefly described. Received: 5 July 2001 Accepted: 19 November 2001     

Ruggedness testing in analytical chemistry

Very high standards of accuracy and precision are currently expected from analytical methods. This is particularly true for pharmaceutical applications, due not only to the potential toxicity of drugs but also to the strict controls of regulatory bodies. This paper deals with the validation of methods by testing ruggedness to changes in the analytical method conditions. As a ruggedness test examines a number of variables simultaneously and hence a large experimental response surface, the design has to be carefully chosen. Advice is offered on the test design, including the selection of factors and the levels at which to test them. Some results are shown for high-performance liquid chromatography methods.     

Resistance of nanostructured films to permeation by industrial pollutants

The aim of this study was to modify or replace the PEVA foil (polyethylenevinylacetate) currently used in the Czech Army as a construction material for the NBC protective disposable suit JP-90 (a part of the OM-90 protective mask set). This material shows inadequate protective properties; therefore, barrier coatings based on melamine, Parylene (polyparaxylylene) and various types of SiO _x were applied to its surface by vacuum technologies. The selected samples coated with polymer matrix barrier nanocoatings were continuously evaluated for resistance to permeation by highly toxic chemicals warfare agents (CWAs) and industrial pollutants at the Military Technical Institute of Protection (MTIP) in Brno. In addition, the microstructure of selected samples was assessed before and after the exposure to pollutants. The nanocoatings thus prepared were characterised in terms of surface morphology (SEM), chemical structure (FTIR), and oxygen transmission rate (OTR) at the Faculty of Chemistry, Brno University of Technology. Sulphur mustard (HD) was used to test the sample resistance to permeation. Cyclohexane and subsequently 1,6-dichlorhexane were used as substitute testing substances for HD; however, the latter proved to be more advantageous. The resulting OTR values are presented, along with the permeation by toxic substances, both for the initial uncoated and the barrier-layers-coated PEVA foil. The results show a difference in the mechanism of vapour permeation of CWAs and toxic volatile organic solvents (VOCs).     

Proficiency testing as a tool to assess the performance of visual TLC quantitation estimates

The use of rapid and inexpensive nonlaboratory-based screening tests for drug quality assessments is recommended as a component of a drug quality assurance program in poor resource settings. We have established routine Minilab test procedures to screen product quality and a proficiency testing program to determine the competency of the inspectors and reliability of results. Samples for the proficiency testing were prepared by pulverizing a standard reference tablet of the appropriate drug and making serial dilutions with starch to obtain concentrations of 0, 40, and 100%. The samples, which were labeled only with the drug name and an identifying letter, were given to inspectors for quality screening using Minilab procedures. In round 1 of the proficiency test, only 3 of 28 substandard samples were correctly identified. Round 2 of the proficiency test, which was administered after a performance qualification test for the analytical method, showed much improvement: 19 of 27 substandard drugs were correctly identified, while 5 out of 9 inspectors made the correct inference on the quality of 45 samples. However, in both rounds, 2 inspectors failed to identify substandard samples, indicating that their technical competencies need to be improved for the reliability of the results. Although the thin-layer chromatography screening methods provide a rapid means for drug quality assessment, they need to be put in the hands of competent users. The inclusion of a proficiency test in the screening program provides a measure of determining competency of the personnel and reliability of the results.     

Improving the Reliability of Analytical Data in the Determination of Trace Elements in Soils

Using the direct x-ray fluorescence determination of Ba, Sr, Zr, and Zn in soils as an example, it was shown that the nature of the test material as well as the biogeochemical properties of the analytes should be taken into account for improving the reliability of analytical data in determining trace elements in soils.     

红外光谱仪模拟空间原位分析表征系统的研制

对现有傅里叶红外光谱仪进行拓展开发,空间模拟试验系统通过法兰与外置原位真空池及光谱仪相连接,实现样品推送机构的建立.分析单元与主真空室之间采用双闸板阀联用实现双向密封,可独立对材料表面进行快速原位分析.摩擦试样可通过样品精密传送和定位装置移动至分析单元进行表征,实现了模拟空间环境下摩擦表面的原位分析功能,将润滑材料的空间摩擦学行为与其表面及化学状态准确关联,避免环境对摩擦表面的污染,为设计新型空间润滑材料提供可靠的试验依据.     

A new test for 'sufficient homogeneity'

Certified reference materials and materials distributed in proficiency testing need to be 'sufficiently homogeneous', that is, the variance in the mean composition of the distributed portions of the material must be negligibly small in relation to the variance of the analytical result produced when the material is in normal use. The requirement for sufficient homogeneity suggests the use of a formal test. Such tests as have been formulated rely on the duplicated analysis of the material from a number of portions, followed by analysis of variance. However, the outcome is not straightforward. If the analytical method used is very precise, then an undue proportion of the materials will be found to be significantly heterogeneous. If it is too imprecise, the test may be unable to detect heterogeneity. Moreover, the Harmonised Protocol Procedure (M. Thompson and R. Wood, Pure Appl. Chem., 1993, 65, 2123) seems to be unduly prone to the rejection of material that is in fact satisfactory. We present a simple new statistical approach that overcomes some of these problems.     

Development of a reference material for residues of chlorfluazuron and fluazuron in beef fat ACSL CRM 3

A beef fat sample was prepared and tested as candidate reference material for the pesticides chlorfluazuron (CFZ) and fluazuron (FZN). An analytical method employing HPLC with UV absorbance detection was developed for homogeneity and stability testing. The material consisted of beef fat spiked with acetone solutions of CFZ and FZN to achieve concentrations close to 1.0 mg/kg for each compound. The coefficients of variation of 7 analyses carried out to test between-jar homogeneity were 1.8% and 2.3% for FZN and CFZ, respectively. No instability of CFZ was detected over a three month period. The candidate reference material was found to be suitable for certification by interlaboratory testing.     

Uncertainty of Qualitative Chemical Analysis: General Methodology and Binary Test Methods

Some general problems of qualitative chemical analysis are considered. In particular, the context of its development is outlined, the concept of hypothesis testing as a basis for the detection and identification of chemical substances is presented, a classification of the types of analysis is given, and the uncertainty (reliability, accuracy) of qualitative determinations is discussed. Various errors arising from the use of binary test methods are reviewed, and methods for estimating these errors are surveyed. The estimates are based on the false (or true) rates of positive and negative results. The concentration dependence of these rates is discussed. It is shown that the testing results become more reliable if the prior probability of the presence of the analyte in the sample is known. Another method for improving the validity of analysis is to use two test methods or to confirm the testing data by other analytical means. In these cases, the positive and negative predictive values are estimated using Bayesian statistic. The approaches to the estimation of the uncertainty of test methods widely used in medicine and toxicology are extended to qualitative chemical analysis as a whole.     

Combustion of PVC: Summary of Main Lecture'

Although polyvinyl chloride) is resistant to ignition due to its chemical structure and its mode of decomposition, it will undergo thermal degradation under high thermal or fire exposure. While considerable literature exists on the mechanism of decomposition of PVC, more recent analytical studies have focused on the forced combustion of PVC and the toxicity of those combustion products. Our analytical studies have involved the analysis of combustion products from rigid PVC, flexible PVC, modified flexible PVC, and PVC-wood mixtures. While analytical studies like this cannot predict biological response, they do demonstrate the nature of experimental problems and experimental design in biological testing.     

X射线荧光光谱扫描法在实物地质资料中应用的可行性探讨

实物地质资料的定量无损检测对于地质学研究具有十分重要的意义,在国外x射线荧光光谱（XRF）扫描分析方法在岩芯分析测试方面的应用研究,已取得了十分显著的成果。XRF岩芯扫描分析方法具有分析速度快、无损检测、连续定量测试多元素和样品制备简单等特点,在获取高分辨测试方面更具独特的优势。因此,这一分析方法在实物地质资料分析方面具有极好的应用前景,它能提高分析的准确性和精确度,降低分析测试成本,保护实物地质资料的完整性,加强实物资料的整体性研究,为实物地质数据采集与信息共享提供更加准确的数据。从介绍XRF岩芯扫描分析方法的原理、特点、影响因素、分析结果的校正人手,进而探讨该测试方法在实物地质资料中应用的可行性。     

Polymerase chain reaction technology as analytical tool in agricultural biotechnology

The agricultural biotechnology industry applies polymerase chain reaction (PCR) technology at numerous points in product development. Commodity and food companies as well as third-party diagnostic testing companies also rely on PCR technology for a number of purposes. The primary use of the technology is to verify the presence or absence of genetically modified (GM) material in a product or to quantify the amount of GM material present in a product. This article describes the fundamental elements of PCR analysis and its application to the testing of grains. The document highlights the many areas to which attention must be paid in order to produce reliable test results. These include sample preparation, method validation, choice of appropriate reference materials, and biological and instrumental sources of error. The article also discusses issues related to the analysis of different matrixes and the effect they may have on the accuracy of the PCR analytical results.     

Correction of a calibration scale for the rapid visual semiquantitative determination of phosphate ions in agricultural samples

A procedure was developed of fabricating a colored calibration scale for determining phosphate ions in aqueous solutions. The procedure is suitable for correcting hue steps depending on the analytical range of phosphate ions. A rapid procedure was proposed for visual testing in a blister cell with a bulk mixture of dry reagents. A test effect was observed immediately after the cell was opened and several drops of a test solution were added. Mixture compositions were developed for the visual determination of phosphate ions in a concentration range of 0.5–80 mg/L by the formation and reduction of phosphomolybdic acid using auxiliary reagents.     

Validation of accuracy by interlaboratory programme

A statistical design is proposed for assessing the accuracy of an analytical method by its application to a certified reference material in an interlaboratory programme. The validation of accuracy is based on the difference between the certified value and the overall mean of the test programme and is linked to the concept that below a certain limit this difference has no practical significance. It is shown that a certified reference material cannot be used to detect bias in a method if the bias is smaller than the confidence interval of the certified value.     

Experimental investigation on the yield loci of PA66

Compression, tensile and mixed compression/shear tests were performed on PA66 by using a universal material testing machine in order to identify the experimental yield loci of PA66. For the mixed compression/shear tests, instead of using a complex loading device, SCS (shear-compression specimens) were used to generate the additional shear stresses. Then, the mechanical behavior of materials under complex stress states can be obtained for further analysis. Results show that the experimental yield loci of PA66 obtained by the test method proposed in the present paper agree well with the theoretical model based on three stresses invariant, which indicates the reliability of the test method.     

A Device for Preparing Standard Mixtures of Carbon Monoxide

Abstract

Accurate low concentrations of carbon monoxide, at levels comparable with those found in ambient air, are prepared by permeation through a thin silicone membrane at a constant temperature. The lowering in CO pressure into a diffusing phial is a measure of permeation rate. The device described permits the dynamic calibration and testing of atmospheric CO analyzers.     

Validation of an analytical method to quantify the permeation and penetration of flurbiprofen into human pharynx tissue

The aim of this investigation was to develop receiver and extraction fluids, and subsequently validate an analytical method to quantify the permeation and penetration of flurbiprofen into human pharynx tissue using a Franz diffusion cell. The solubility and stability of flurbiprofen in a suitable receiver fluid, and a suitable extraction method and fluid to recover and quantitate flurbiprofen from human pharynx tissue, were investigated using high‐performance liquid chromatography (HPLC). The potential interference of human pharynx tissue in the receiver fluid was also investigated. The HPLC analytical method was successfully validated according to current guidelines. The final receiver fluid demonstrated sufficient solubility and stability, and the extraction method and fluid resulted in >95% recovery of flurbiprofen following exposure to human pharynx tissue. The lower limit of quantitation of flurbiprofen was 0.045 μg/mL in both the receiver and extraction fluids. There was no interference of the human pharynx tissue with the HPLC method. This investigation validated an analytical method for quantitating flurbiprofen, and determined a suitable receiver fluid and extraction method and fluid, which can be used to investigate the permeation and penetration of flurbiprofen through human pharynx tissue using the Franz diffusion cell method.     

Evaluating the significance threshold in robustness testing. A critical discussion on the influence of time in molecular fluorescence spectrometry

Robustness experiments are performed in analytical chemistry to assess the behaviour of an analytical procedure under conditions slightly different from those of the experimental optimum. This work presents a study of robustness applied to a previously proposed fluorescent methodology using two replicated 2(7-4) saturated fractional factorial designs. A comparison is established between three different ways to test the significance of the effects of the variables involved on the response signal. Critical discussions about the most appropriate threshold to be introduced when testing for significance of the factors and the influence of the time necessary to carry out the experiments are included.     

Interactive programme for evaluation of circular analyses (IPECA)

A PC-based interactive programme is described which is designed to help in suggesting the best estimate of the true value of an analyte content from results of collective studies aiming at deriving consensus values and/or reference material preparation by employing combined statistical and analytical considerations. The Grubbs, Dixon, Huber tests, and the coefficients of skewness and curtosis tests are used for outlier detection, the Bartlett, Cochran, and the standard error tests are employed for testing variance homogeneity testing and/or variance outliers identification, while the normality of results distribution is tested according to the Kolmogoroff-Smirnoff-Lilliefors and Shapiro-Wilk tests. One-way analysis of variance (ANOVA) is employed to test differences among means of results obtained in different conditions (laboratories, analytical methods, etc.) and to calculate the overall mean and its confidence interval accordingly. Points for an analytical discussion are given which should be considered prior to a decision whether a result of a trace element determination, identified as an outlier from statistical reasons, should be rejected.