Quality assurance assay performance

McConnell RJ, Fitzgerald SP, Lamont JV (1992) Trenbolone and 19-nortestosterone residue analysis by immunoaffinity chromatography and high-performance liquid chromatography and/or an enzyme-linked immunosorbent assay. In Morgan MRA, Smith CJ, Williams PA (eds) Food safety and quality assurance applications of immunoassay systems. Elsevier, Barking, p 245... 

Although a thorough validation cannot rule out all potential problems, the process of method development and validation would address the most common ones. Examples of typical problems that can be minimized or avoided include interferences that coelute with the analyte in liquid chromatography (LC), a particular type of column that no longer produces the separation needed because the supplier of the column has changed the manufacturing process, an assay method that is unable to achieve the same detection limit after a few weeks, or a quality assurance audit of a validation report that finds no documentation on how the validation was performed. 

The molar absorptivity (e) of a known molecule is constant under identical conditions of solvent, concentration and path length, and can be used to quantify the amount of a particular pharmaceutical in a tablet. Such assays form the basis of many quality assurance procedures in the pharmaceutical industry, and have been extensively used by the British Pharmacopoeia (B.P.). More recently, however, high-performance liquid chromatography (HPLC) has replaced UV analysis in many B.P. assays, as most industrial analyses routinely use HPLC. 

Quality Control Data. Data obtained from assays of blood gas and pH control materials may be handled in the same way as data from other clinical chemistry determinations (i.e., mean, SD, and coefficient of variation, and control and confidence limits for construction of Levey-Jennings plots). As stability of commercial aqueous control materials is generally several months, vendors often provide data reduction programs that standardize and simplify documentation. However, the resulting reports are temporally delayed and are most useful for meeting accreditation requirements as opposed to real-time corrective or preventive action. They are however useful to compare long-term performances with other laboratories. Equally important features of quality assurance to an active blood gas service are the sixth sense of practiced operators for detecting subtle manifestations of deterioration of instrument performance and the suspicion of trouble expressed by clinicians. 

Every laboratory takes great pains to ensure that the methods in use continue to produce reliable results. Laboratory staff monitor performance of assays using quality control samples to give rcassunince that the method is performing satisfactorily with the patients. specimens. The.se are internal quality controls which are analysed every day or every time an assay is run. The expected values are known and the actual results obtained are compared with previous values to monitor performance. In external quality assurance schemes, identical samples arc distributed to laboratories results are then compared. 

External Quality Assurance (EQA) schemes attempt to provide an independent assessment of a laboratory s performance usually with respect to a defined assay. Such schemes complement (and use) ICQ. The basis of the schemes is... 

The highest sensitivity and selectivity in vitamin E LC assays are obtained by using fluorescence or electrochemical detection. In the former, excitation at the low wavelength (205 nm) leads to improved detection limits but at the expense of selectivity, compared with the use of 295 nm. Electrochemical detection in the oxidation mode (amperometry or coulometry) is another factor 20 times more sensitive. In routine practice, however, most vitamin E assays employ the less sensitive absorbance detection at 292-295 nm (variable wavelength instrument) or 280 nm (fixed wavelength detectors). If retinol and carotenoids are included, a programmable multichannel detector, preferably a diode array instrument, is needed. As noted previously, combined LC assays for vitamins A, E, and carotenoids are now in common use for clinical chemistry and can measure about a dozen components within a 10 min run. The NIST and UK EQAS external quality assurance schemes permit interlaboratory comparisons of performance for these assays. 

As with all modern analytical programs, an essential keystone for success is a sound analytical quality control and assessment strategy, which should always, where possible, include the exchange of samples between different analytical laboratories and the use of round-robin external quality assurance schemes. External schemes for folate and cobalam-ins are already in existence in several countries some other water-soluble vitamin assays are performed regularly by a sufficient number of different laboratories for external sample exchange schemes to be feasible and cost-effective, while others are too specialized and perhaps too rarely performed for regular... 

Creatinine method check. At least once daily run a CREA test on a solution of known creatinine activity such as an assayed control or calibration standard other than that used to calibrate the CREA method. For further details review the Quality Assurance Section of the Chemistry Manual. The result obtained should fall within acceptable limits defined by the day-to-day variability of the system as measured in the user s laboratory. (See SPECIFIC PERFORMANCE CHARACTERISTICS for guidance.) If the result falls outside the laboratory s acceptable limits, follow the procedure outlined in the Chemistry Troubleshooting Section of the Chemistry Manual. 

Experience has shown that these assays can perform exceeding well but only if the user belongs to an external quality assurance scheme (EQAS) which monitors performance and uses target values determined by GC-MS (e.g., 170). Table 8 illustrates some GC-MS methods which have been published in the last 20 years, not all of which are suitable for use as reference methods. 

Compositional determinations Assays Specific determinations Qualitative Quantitative Understand the chemistry responsible for proper/improper product performance Provide technical leads for new developments Assure product quality Correct product problem Understand competitor s products Regulatory compliance Develop new products... 

Several in vitro tests are currently employed to assure drug product quality. These include purity, potency, assay, content uniformity, and dissolution specifications. For a pharmaceutical product to be consistently effective, it must meet all of its quality test criteria. When used as a QC test, the in vitro dissolution test provides information for marketing authorization. The dissolution test forms the basis for setting specifications (test, methodology, acceptance criteria) to allow batch release into the market place. Dissolution tests also provides a useful check on a number of physical characteristics, including particle size distribution, crystal form, etc., which may be influenced by the manufacturing procedure. In vitro dissolution tests and QC specifications should be based on the in vitro performance of the test batches used in in vivo studies or on suitable compendial specifications. For conventional-release products, a single-point dissolution... 

The application of quality control procedures to ensure that satisfactory analytical performance of enzyme assays is maintained on a day-to-day basis is complicated by the tendency of enzyme preparations to undergo denaturation with loss of activity. This maltes it difficult to distinguish between poor analytical performance and denaturation as possible causes of a low result obtained for a control sample introduced into a batch of analyses. Assured stability within a defined usable time span is therefore the prime requirement for enzyme control materials, as it is for enzyme calibrators. However, specifications for the two types of materials can differ in other respects. Because the function of a calibrator is to provide a stated activity under defined assay conditions, it is not necessary for it to show sensitivity to changes in the assay system identical to those of the samples under test therefore within certain Umits, enzymes from various sources can be considered in the search for stability. However, it is the function of a control to reveal small variations in reaction conditions, so it must mimic the samples being analyzed. The preparation of enzymes from human sources is not by itself a guarantee of an effective control. For example, human placental ALP is very stable, but it differs significantly in kinetic properties from the liver and bone enzymes that contribute most of the ALP activity of human serum samples it is therefore not an ideal enzyme for use in control material for the determination of ALP. 

In current industrial practice gas chromatographic analysis (glc) is used for quality control. The impurities, mainly a small amount of water (by Karl-Fischer) and some organic trace constituents (by glc), are determined quantitatively, and the balance to 100% is taken as the acetone content. Compliance to specified ranges of individual impurities can also be assured by this analysis. The gas chromatographic method is accurately correlated to any other tests specified for the assay of acetone in the product. Contract specification tests are performed on product to be shipped. Typical wet methods for the determination of acetone are acidimetry (49), titration of the liberated hydrochloric acid after treating the acetone with hydroxylamine hydrochloride and iodimetry (50), titrating the excess of iodine after treating the acetone with iodine and base (iodoform reaction). 

For stability studies, it is likely several of these types of assays will be used, each providing information on different characteristics of the molecule or information on the different types of degradation pathways. It is common that many tests (relative to what is performed for small molecules) are performed to characterize a biologic substance or product to give assurance of potency, purity, and quality. Table 17.1 (see section 17.3 ) gives a quick comparison of the differences between a biologic and small molecule drug product. 

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