A pilot study of routine quality control of sampling by the SAD method, applied to packaged and bulk foods

A recently proposed method of looking at sampling uncertainty has been tested by its application to the sampling and analysis of several types of food and an animal feedstuff. In this 'SAD' method, increments comprising the conventional sample (that is, collected in the fashion prescribed by the standard sampling protocol) are allocated to either of two equal sized 'splits', which are prepared and analysed separately. The absolute difference between the analytical results for the two splits (the split absolute difference, or SAD) is plotted on a one-sided control chart. A non-compliance indicates that the combined uncertainty of sampling or analysis is larger than expected and the result of the measurement (the mean of the two split results) is possibly not fit for purpose. In addition, the SAD results give rise to a rugged estimate the uncertainty associated with the sampling protocol, often a major part of the total measurement uncertainty.     

Evaluation of statistical control charts for on-line radiation monitoring

Statistical control charts are presented for the evaluation of time series radiation counter data from flow cells used for monitoring of low levels of ⁹⁹TcO₄⁻ in environmental solutions. Control chart methods consisted of the 3-sigma (3σ) chart, the cumulative sum (CUSUM) chart, and the exponentially weighted moving average (EWMA) chart. Each method involves a control limit based on the detector background which constitutes the detection limit. Both the CUSUM and EWMA charts are suitable to detect and estimate sample concentration requiring less solution volume than when using a 3σ control chart. Data presented here indicate that the overall accuracy and precision of the CUSUM method is the best.     

新的脉冲进样AAS法测定“麻杏石甘汤”中的微量金属元素

本文研制了一种新的脉冲进样装置，用于火娄原子吸收分光光度法测定中药煎剂中的Ｃａ，Ｍｇ，Ｆｅ，Ｍｎ，Ｚｎ五种金属元素含量，实验表明，利用此种装置可以同时获得两种进样方式的分析结果，线性范围比常规法宽两倍，耗样量，精密度及分析速度均优于常规法。     

Computerized image processing for evaluation of sampling error in ion microprobe analysis

A method is described for the microscale evaluation of sample heterogeneity as applied to in-situ ion microprobe analysis. Computer feature analysis of digitized ion images is utilized to generate sampling constants, which can be related to the degree of heterogeneity present for a particular constituent in the sample. The expected precision for a series of analyses, or the number of analyses required for a desired precision can also be determined. This approach, which is experimentally verified for NBS SRM-664 low-alloy steel, can be used both to minimize sampling error and to assess the applicability of specific reference materials to microprobe analysis.     

Uncertainty of sampling in chemical analysis

 Uncertainty of sampling is the contribution from sampling errors to the combined uncertainty associated with an analytical measurement when the measurand is the concentration of the analyte in the 'target', the total bulk of material that the sample is meant to represent. Of the errors considered to contribute to uncertainty, random errors of sampling, characterised by precision, are much more accessible to investigation than those due to bias. Where an approximation to random sampling can be achieved, realistic precisions can normally be estimated. In some instances reproducibility precision is significantly greater than repeatability precision, and the contribution of between-sampler variations to sampling uncertainty must be acknowledged. However, the collaborative trial of a sampling method is an expensive and difficult exercise to execute. A system of internal quality control for routine sampling can be introduced. Fitness for purpose has been defined in terms of the required combined uncertainty of sampling and analysis. Received: 4 November 1997 · Accepted: 26 November 1997     

Uncertainty in analyte mass for samples containing small numbers of particles.

A sampling equation was derived that relates the standard deviation in analyte mass to the number of particles in the sample, the fractions of the different types of particles in the mixture and the masses and analyte concentrations of the individual particles. The equation, which is applicable to samples containing any number of particles, was verified by sampling and analysis of two cereal grain mixtures for manganese, potassium, chlorine and magnesium, and by Monte Carlo computer simulation. Comparison of the sampling precision of analyte mass with the analytical measurement precision was also studied, and it was shown that use of the equation allows the calculation of the minimum number of particles required to hold the sampling relative standard deviation to that of the analytical measurement.     

A new internal quality control chart based on biological variation

The instruments and analytical methods currently used in clinical laboratories today have better precision and stability than those used in the past. With the development of chemical and immunological methods and instrumentation technology, test precision has increased. However, the application of the Westgard multirule procedure to control sera in the Levey-Jennings chart may not be useful or cost-effective. We devised a new test-specific decision limit for accepting or rejecting runs based on the data of within-subject biological variation and prepared a control chart. We then applied these new limits and control chart to a group of tests performed in our laboratory. With the exception of the tests for albumin, total protein, and calcium, for which desirable performance standards could not be attained with the current technology and methodology, the application of these control limits was cost-effective and convenient. It is estimated that the value of healthy within-subject biological variations is constant, irrespective of the methodology, the area in which the study has been performed, and the number of subjects included in the study. We believe that control limits based on biological variation are reliable and cost-effective, and may be useful in modern and accredited laboratories.     

Automated polarographic analysis: Part II. Response time and precision studies

A systematic study of various experimental parameters which may influence the response time and precision of an automated polarographic system is described. The effects of segmented streams, flow rate, pump stop during sample shifts, debubbler position, current damping, scale expansion, sampling rate and type of deaerating gas are discussed. Low response times are favoured by the use of segmented streams, a high aspiration rate, a short distance between the debubbler and the working electrode and a low current damping, while the best precision is obtained by using scale expansion, pump stop during sample shifts, a low sampling rate and argon gas for deaeration. Under optimized conditions a standard deviation of 0.3 % was obtained.     

On the sampling variance of ultra-dilute solutions

Contemporary analytical methodology allows the determination of substances in ultra-dilute solutions, i.e. picomol per liter (pM) and lower, by employing a wide spectrum of techniques. The reduction of both sample volume and quantification limits made possible the determination of zeptomol amounts of analytes. Among the many problems associated with the analysis of this kind of sample is the relatively high intrinsic sampling variance which restricts the attainable overall analytical precision. This sampling variance is due to the quantized nature of matter. The expected sampling variance can be calculated considering that the limited number of analyte molecules per test-portion is subjected to Poisson distribution.     

Determination of volatile organic compounds in ambient air. Comparison of methods

Two analytical methods for the determination of benzene vapour in ambient air are compared in this paper. The methods differ from each other in the sampling technique, type of sorbent, method of extraction and method of detection. The investigation of the methods using various techniques for sample analysing showed a significant influence of the way in which the analysis is carried out, on the final result of the analysis. Calculation of the standard deviations, relative standard deviations and confidence intervals allowed for assessment of the precision and repeatability of the methods. Of the two examined methods, that using an automated system of contaminant sampling and thermodesorption was more precise. This method has been applied to measurements of concentrations of benzene, toluene and xylenes in ambient air.     

A novel device for the accurate dispensing of small volumes of liquid samples

A sample dispenser with electronic control of delivered volume has been designed and evaluated. With this device, liquid samples are dispensed in the form of uniform droplets less than 4 nl in volume; total volumes as small as 40 nl can be delivered with 1.5% precision. Important features of the microdroplet formation process have been studied and the effect of sample solution concentration and viscosity have been examined. The dispenser is expected to find application in several areas, including electrothermal atomization atomic absorption spectrometry, automated titrimetry, and high-precision, low-volume solution sampling.     

质量控制图用于石墨炉原子吸收光谱法检测海水中铅元素

为保证海水中重金属检测结果的准确可靠,以铅元素为例,每个工作日使用石墨炉原子吸收光谱仪平行测定铅质控样2次,收集20组有效数据后,通过计算均值、标准差得出上下控制限、警告线及辅助限,绘制出在当前实验室环境条件、仪器设备、试剂药品和人员水平等因素条件下的质量控制图。该质量控制图不仅用于实际检测过程中对检测结果进行监控,还可为该实验室的人员考核、留样复测等实验室质量控制行为提供结果判定依据。     

Application of direct solid analysis of plant samples by electrothermal vaporization-inductively coupled plasma atomic emission spectrometry: Determination of Cd and Si for environmental purposes

Elemental determinations are usually performed on plant samples for agronomic or environmental studies. Direct solid sampling is possible when electrothermal vaporization (ETV) is used as a method of sample introduction in inductively coupled plasma atomic emission spectrometry (ICP-AES). ETV-ICP-AES was applied for elemental determinations in plant samples. The first application aimed at Cd determinations in very small size plant material samples. Several reference plant materials were used to validate the accuracy of the method. Quality control included the systematic analysis of a reference sample in each batch of unknown samples. The performance of the method in time was illustrated by a control chart. The second application aimed at the content of Si in plant materials. Quantification of Si in plant samples was carried out using samples issued from an inter-laboratory test. Detection limit of 30 μg g^− 1 was achieved for Si. In all cases, quantification was accomplished easily by means of aqueous standard solutions deposited on cellulose support.     

Uncertainty in analytical results from solid materials with electrothermal atomic absorption spectrometry: a comparison of methods

The combined uncertainty in the analytical results of solid materials for two methods (ET-AAS, analysis after prior sample digestion and direct solid sampling) are derived by applying the Guide to the Expression of Uncertainty in Measurement from the International Standards Organization. For the analysis of solid materials, generally, three uncertainty components must be considered: (i) those in the calibration, (ii) those in the unknown sample measurement and (iii) those in the analytical quality control (AQC) process. The expanded uncertainty limits for the content of cadmium and lead from analytical data of biological samples are calculated with the derived statistical estimates. For both methods the expanded uncertainty intervals are generally of similar width, if all sources of uncertainty are included. The relative uncertainty limits for the determination of cadmium range from 6% to 10%, and for the determination of lead they range from 8% to 16%. However, the different uncertainty components contribute to different degrees. Though with the calibration based on reference solutions (digestion method) the respective contribution may be negligible (precision < 3%), the uncertainty from a calibration based directly on a certified reference material (CRM) (solid sampling) may contribute significantly (precision about 10%). In contrast to that, the required AQC measurement (if the calibration is based on reference solutions) contributes an additional uncertainty component, though for the CRM calibration the AQC is “built-in”. For both methods, the uncertainty in the certified content of the CRM, which is used for AQC, must be considered. The estimation of the uncertainty components is shown to be a suitable tool for the experimental design in order to obtain a small uncertainty in the analytical result.     

The importance of precision in sampling sludges, biowastes and treated soils in a regulatory framework

As part of the European Commission (EC)'s revision of the Sewage Sludge Directive and the development of a Biowaste Directive, there was recognition of the difficulty of comparing data from Member States (MSs) because of differences in sampling and analytical procedures. The ‘HORIZONTAL' initiative, funded by the EC and MSs, seeks to address these differences in approach and to produce standardised procedures in the form of CEN standards. This article is a preliminary investigation into aspects of the sampling of biosolids, composts and soils to which there is a history of biosolid application. The article provides information on the measurement uncertainty associated with sampling from heaps, large bags and pipes and soils in the landscape under a limited set of conditions, using sampling approaches in space and time and sample numbers based on procedures widely used in the relevant industries and when sampling similar materials.These preliminary results suggest that considerably more information is required before the appropriate sample design, optimum number of samples, number of samples comprising a composite, and temporal and spatial frequency of sampling might be recommended to achieve consistent results of a high level of precision and confidence.     

Multivariate control charts based on NAS and mid‐infrared spectroscopy for quality control of B5 blends of methyl soybean biodiesel in diesel

In this work, mid‐infrared spectroscopy and multivariate control charts based on net analyte signal were applied for quality control of B5 blends of biodiesel/diesel (5% biodiesel/95% diesel). Control charts were constructed using instrumental signal decomposition, generating three charts: the net analyte signal chart for monitoring the analyte of interest (methyl soybean biodiesel); the interference chart, which corresponds to the contribution of all other compounds in the diesel sample (diesel); and the residual chart, which corresponds to non‐systematic variations. Statistical limits were established for each developed chart, using samples inside quality specifications (normal operation conditions). To validate multivariate control charts, new samples were analyzed. The new samples represented samples in‐control and samples out‐of‐control in relation to the content of biodiesel, adulterated biodiesel with severe vegetable oils and adulterated diesel with residual automotive lubricant oil, kerosene, and gasoline. The results obtained show an excellent distinction between the samples inside and out of the quality specifications, with 91% and 100% correctly classified, respectively, which demonstrates that the methodology developed is a viable alternative for quality monitoring of this type of fuel. Copyright © 2015 John Wiley & Sons, Ltd.     

Microdetermination of carbon and hydrogen in organic compounds using flushed-oxygen combustion tube

A rapid method of microanalysis for carbon and hydrogen in organic compounds using an empty combustion tube fused with two nozzles for flushing oxygen and employing reduced copper for the reduction of nitrogen oxide was investigated. A sample was decomposed rapidly in a sample heater for 2 min, and the gasified vapor was transported to the stationary combustion zone heated at 850 °C, where oxygen was flushing from two nozzles, the oxygen flow was then replaced with nitrogen for 3 min until all the combustion products were swept out towards the absorption train. The sample size was suggested to be around 1 mg for this rapid method, using a Mettler UM6, or an electrobalance having equal precision for the sampling.     

基于机器人制样和激光诱导击穿光谱分析技术的选煤厂检测系统无人化

目前选煤厂煤质检测过程自动化程度低,采样与制样技术需要大量的人工参与。检测技术的落后直接影响数据的准确性从而对整个选煤厂生产过程控制与产品质量控制产生重要影响,直接关系选煤厂的经济效益。面对产业升级的需要,将先进的自动采制样技术引进煤炭生产经营企业是当务之急。机器人采制样系统包含:机械化采样与初制样技术、机器人精细化制样技术、煤炭快速检测技术、自动快速浮沉技术,为选煤厂提供了一种全自动采制检的新技术方案。