Measurement techniques analytical quality control

The debate over techniques (1) and (2) initially centered on the main component of the analytical technique (i.e., wet-UV or dry-high temperature ) but it has become apparent that the most significant difficulties with this measurement are more to do with analytical quality control issues such as the use of appropriate blanks, strict control of day-to-day operating conditions, and great care in calibration procedures. A very recent report by Sharp and coworkers on an extensive intercalibration exercise states that Experienced oceanic analysts, with internal or shared reference materials, can now show reproducibility and comparability at a level closer to 2% . The development of DOC reference materials is in its early stages and once such materials are reliably available then the DOC issue should settle down as a difficult but essentially routine measurement. 

Particularly for direct microanalytical techniques using <10 mg of sample for analysis, it is highly desirable to obtain quantitative information on element- and compound-specific homogeneity in the certificates for validation and quality control of measurements. As the mean concentration in a CRM is clearly material-related, the standard deviation of this mean value should represent the element s distribution in this matrix rather than differences in the analytical procedures used. 

Baseline separation of the cephalosporin antibiotic cephradine, its main impurity cephalexin, and other related impurities was achieved by MEKC. The method was validated in compliance with the USP XXII analytical performance parameters and the results were comparable with a validated LC method, depicting CE to be a valuable alternative technique to LC in pharmaceutical quality control. In most cases, the amount of impurities relative to the main compound measured by MEKC is similar to that obtained by LC. However, some reports reveal that there are differences in number and amount of impurities between MEKC and LC analysis. MEKC permitted the determination of seven known and three unknown impurities in cefotaxime and the results were in good agreement with those of LC. ° MEKC yielded a higher amount of the cefotaxime dimer but a lower amount of an unidentified impurity with respect to LC. The differences may be due to the easier formation of the dimer in the aqueous sample solvent used in MEKC compared to the hydroorganic... 

In many pharmaceutical companies, quality control departments already use NIRS to identify formulations. Figure 23 illustrates a PLS calibration for the active content determination in a low-dose tablet. Once identity testing is passed, it is straightforward to consider as a next step the determination of active content in intact tablets. Thus, qualitative and quantitative analysis can be performed by acquiring a single NIR spectrum per sample. Two analytical techniques are replaced by one—nondestructive—NIR measurement. For this purpose near-infrared spectroscopy is a fast and powerful alternative to traditional analysis, which only remains necessary as reference analytics. 

One of the most common laboratory techniques for determining the concentration of a solute is titration. Titrations are used daily to monitor water purity and blood composition, and for quality control in the food industry. The solution being analyzed is called the analyte, and a known volume is transferred into a flask. Then a solution containing a known concentration of reactant is measured into the flask from a narrow calibrated cylinder called a buret until all the analyte has reacted (Fig. L.2). The solution in the buret is called the titrant, and the difference between the initial and final volume readings of the buret tells us the volume of titrant that has drained into the flask. The determination of concentration or amount by measuring volume is called volumetric analysis. 

When the analytical laboratory is not responsible for sampling, the quality management system often does not even take these weak links in the analytical process into account. Furthermore, if sample preparation (extraction, cleanup, etc.) has not been carried out carefully, even the most advanced, quality-controlled analytical instruments and sophisticated computer techniques cannot prevent the results of the analysis from being called into question. Finally, unless the interpretation and evaluation of results are underpinned by solid statistical data, the significance of these results is unclear, which in turn greatly undermines their merit. We therefore believe that quality control and quality assurance should involve all the steps of chemical analysis as an integral process, of which the validation of the analytical methods is merely one step, albeit an important one. In laboratory practice, quality criteria should address the rationality of the sampling plan, validation of methods, instruments and laboratory procedures, the reliability of identifications, the accuracy and precision of measured concentrations, and the comparability of laboratory results with relevant information produced earlier or elsewhere. 

Quality control is becoming increasingly more significant in analytical chemistry. However, it is presently applied primarily to measurement techniques and not to sample preparation. For quality control in sample decomposition, it is necessary to measure and record certain parameters exactly to be able to subsequently trace the course of the decomposition process. 

Multidimensional techniques are regularly used in analytical assessments of measurement data relating to the levels of chemical elements in the quality control of animal and plant food products. Chemometric interpretations have been obtained for the following animal products meat and meat products [316-318], fish [319-321], seafood [25, 322-328], milk and dairy products [329-332] and honey [333-339]. Similar interpretations have been obtained for the following plant products rice [143], cereals [340], vegetables [140, 341-346], fruit and fruit preserves [347], tea [155, 348-350], coffee [13, 155, 351, 352], mushrooms [26], fruit juices [141], confectionery [21, 353], nuts [354], wine [355-358], beer [66, 359] and other alcoholic beverages [159, 360, 361]. 

In many countries undertaking the most technically demanding analyses, it is expected that the laboratories will be registered under quality assurance schemes. Accuracy and repeatability should be covered by quality assurance requirements, but resolution and detection limits are critically dependent on technique and instrumentation. Details on the general subjects of quality assurance/quality control, quantification of uncertainty in analytical measurements, accreditation of laboratories, and on the general concepts and strategy for ensuring that analytical chemical measurements are comparable - in one word traceability - can be found elsewhere in the chemical literature (26,32-36). 

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