Internal quality control standard

An internal quality control standard with an analyte concentration of 50 mg kg is analysed in a laboratory for 25 consecutive days, the sample size being four on each day. The results are given in Table 4.2, which is in the form of an Excel spreadsheet. Determine the value of R and hence plot control charts for the mean and range of the laboratory analyses. 

The accuracy of the inductively-coupled plasma procedure was assessed by analysing waters of known sulfate composition, and by comparing measured sulfate values for a wide range of samples with those obtained for the same waters by an automated spectrophotometric procedure. Good agreement is obtained between the derived sulfate measurements and the normal values for International Standard Sea Water and an EPA Quality Control Standard. 

Thus, as for the European Union, the requirements are based on accreditation, proficiency testing, the use of validated methods of analysis and, in addition, the formal requirement to use internal quality control procedures which comply with the Harmonised Guidelines. Although the EU and Codex Alimentarius Commission refer to different sets of accreditation standards, the ISO/IEC Guide 25 1990 and EN 45000 series of standards are similar in intent. It is only through these measures that international trade will be facilitated and the requirements to allow mutual recognition to be fulfilled will be achieved. 

As shown above, these include a laboratory to be third-party assessed to international accreditation standards, to demonstrate that it is in statistical control by using appropriate internal quality control procedures, to participate in proficiency testing schemes which provide an objective means of assessing and documenting the reliability of the data it is producing and to use methods of analysis that are fit-for-purpose . These requirements are summarised below and then described in greater detail later in this chapter. 

By using the combination of specific method accreditation and generic accreditation it will be possible for laboratories to be accredited for all the analyses of which they are capable and competent to undertake. Method performance validation data demonstrating that the method was fit-for-purpose shall be demonstrated before the test result is released and method performance shall be monitored by on-going quality-control techniques where applicable. It will be necessary for laboratories to be able to demonstrate quality-control procedures to ensure compliance with the EN 45001 Standard,3 an example of which would be compliance with the ISO/AOAC/IUPAC Guidelines on Internal Quality Control in Analytical Chemistry Laboratories.12... 

Internal quality control (IQC) is one of a number of concerted measures that analytical chemists can take to ensure that the data produced in the laboratory are of known quality and uncertainty. In practice this is determined by comparing the results achieved in the laboratory at a given time with a standard. IQC therefore comprises the routine practical procedures that enable the analyst to accept a result or group of results or reject the results and repeat the analysis. IQC is undertaken by the inclusion of particular reference materials, control materials , into the analytical sequence and by duplicate analysis. 

Standards of analytical methods and requirements fix internal quality control... 

IUPAC, ISO, and AOAC International International Union of Pure and Applied Chemistry, International Organisation for Standardization, Association of Official Chemists Method validation, Standardization, internal quality control, proficiency testing, accreditation 4,8, 62-71... 

Nonconformance arises when any aspect of the work of a laboratory does not conform to its procedures, to the standard, or the agreed-upon requirements of the customer. These are detected by customer complaints, internal quality control measures, management audits and reviews, and by observations of staff. They must be dealt with under the appropriate part of the management system and fully investigated and reported. 

A minimum of 2 ml EDTA blood is placed immediately on ice and centrifuged within 30 min at 2000 xg for 5 min at 4°C. Plasma is immediately deproteinised by adding 1 ml to 0.625 ml of 10% 4 and mixing thoroughly by vortex. The mixture is frozen and stored at -70°C until analysis. 1-ml aliquots of pooled plasma collected from healthy subjects are prepared and stored in the same way and are used to prepare AdoMet and AdoHcy calibration standards to allow for matrix effects and also as an internal quality control. CSF is collected in plain tubes and kept at -70°C until analysis. 

The best indicator of the reliability of the assay is the precision, expressed as the mean and coefficient of variation (CV), of a series of analyses carried out on consecutive days (the between-run variation). In the authors laboratory the internal quality control samples were run in ten series of analyses over a 2-month period. The calculated mean, standard deviation and coefficient of variation are shown in Table 3.3.3. 

For internal quality control, urine from a known MPS patient and a solution containing chondroitin sulfate (50 pg/ml) are used. Results for urine and the artificial control should not exceed 3 standard deviations when plotted over time if it does, the test has to be repeated. In addition, absolute absorption values, the slope of the calibration curve, and the coefficient of variance (CV) of duplicates have to be within certain limits defined by the laboratory. 

The chemical analyses carried out are indicated in Table 15.1. Analytical results produced by the Bagnoli SpA underwent quality controls through use of internationally recognized control standards and duplicated analysis of 5% of the samples at random. Duplicate analysis of 5% of the samples were performed at the British Geological Survey Laboratories. 

Fig. 6 is a computer plot of standard deviation interval for phenytoin over two years in one particular laboratory. The method of using bias relative to some measure of imprecision, which was first introduced in discussing internal quality control, is particularly useful if data are to be plotted by computer. It is also useful for manual analysis as a single chart can be prepared with lines at 0 2 and 3 si which can be copied and used for all analytes. 

The multilocus method discovered by Alec Jeffreys has proved useful in a wide range of animal and plant species and is currently one of the most widely used fingerprinting methods in population studies. This method, using probes 33.6 and 33.15, is the only fingerprinting method for which a formal international quality control system is operated (Zeneca Cellmark Diagnostics), and offers a unique opportunity for the standardization of cell line quahty control procedures in widely distributed laboratories. 

The ISO 17025 standard [3] describes monitoring the quality assurance of test and calibration results by, amongst other means, the regular use of CRMs and/or internal quality control using secondary reference materials and by participation in inter-laboratory comparisons or proficiency testing programmes. 

Results verification is totally different from results validation. Results validation (point 4.7.5. and 5.9. of NBN-EN-ISO-CEI 17025 standard) shows, each year, or when it is judged necessary, that a given laboratory has the capacity to apply a particular method, repetitively, in respect of obtained data during initial validation. Trueness and statistical dispersion of results are the basis of the definition of the uncertainty of the standard of measurement [16] and, in some cases, the basis for the definition of the limit of detection and quantification. Management of data from validation results, as control card, could permit the detection and control of eventual deviation. Validation of results is the internal quality control procedure which verifies the stability of performance of the methods for which accreditation is sought, in the limited-scope procedural context. 

CAC/GL 65-1997, Harmonized Guidelines for Internal Quality Control in Analytical Chemistry Laboratories, Joint FAOAVHO Food Standards Program, 1997 (available at http //WWW.codexalimentarius.net/download/ standards/10920/CXG 065e.pdf accessed 2/23/10). 

Quality control (QC) refers to the operational techniques and activities that are used to fulfill requirements for quality. Internal quality control comprises the routine practical procedures that enable the analytical chemist to make a decision on whether to accept a result or a group of results as fit for purpose, or reject them and repeat the analysis. Tools for quality control include the use of reference standards and certified reference materials, the use of positive (spiked or incurred) and negative control samples and control charts, replicate analyses, and proficiency tests. Quality control in the laboratory is discussed in more detail in Section 10.5 of this chapter. 

The uptake of standard tests can conveniently be gauged by their usage in national, international, and company specifications for materials and products, although the use of tests for internal quality control work and for R D activities should never be underestimated. In specifications, small-scale laboratory tests fall into three broad categories. 

---