Standard accuracy

Before a procedure can provide useful analytical information, it is necessary to demonstrate that it is capable of providing acceptable results. Validation is an evaluation of whether the precision and accuracy obtained by following the procedure are appropriate for the problem. In addition, validation ensures that the written procedure has sufficient detail so that different analysts or laboratories following the same procedure obtain comparable results. Ideally, validation uses a standard sample whose composition closely matches the samples for which the procedure was developed. The comparison of replicate analyses can be used to evaluate the procedure s precision and accuracy. Intralaboratory and interlaboratory differences in the procedure also can be evaluated. In the absence of appropriate standards, accuracy can be evaluated by comparing results obtained with a new method to those obtained using a method of known accuracy. Chapter 14 provides a more detailed discussion of validation techniques. 

Measuring voltage transformers Standard accuracy class may be one of 0.1, 0.2, 0.5, I or 3. The recommended class of accuracy will depend upon the type of metering and generally as noted in Table 15.3. 

Because an infrared result is calculated as if the aromatics in the sample were present in the same ratio as in the calibration standard, accuracy depends on use of a calibration standard as similar to the type of contamination as possible. Use of a dissimilar standard will tend to create a positive bias in highly aliphatic samples and a negative bias in highly aromatic samples. 

International organization for Standardization, Accuracy (trueness and precision) of measurement methods and results, ISO/DIS 5725-1 to 5725-3, Draft versions 1990/91. 

At this temperature the vapor pressure changes about 5% /°C requiring bubbler thermostatting to better than 0.2°C for a 1% standard accuracy. It also is important to know accurately the total pressure at the final bubbler since this is also used in the calculation. This was assumed to be 760 torrs to illustrate the preceding calculation, but must be measured in practice. 

Ion suppression is so far mainly considered in the context of sensitivity and the lower limit of quantification of an assay. But it has to be emphasized that short term variations in ion yields—particularly due to matrix components—can compromise the accuracy of analyses Whenever the variation of ion yield has a differential impact on target analyte and internal standard, accuracy is compromised. This means that the reliability of LC-MS/MS analyses critically depends on (1) how similar the impact of ion suppression or ion enhancement on target analyte and internal standard compound is and on (2) how similar the matrices of calibrator samples and actual patients samples are with respect to the modulation of ionization efficacy. This problem can be of relevance for an entire measuring series—if systematic differences in the ionization modulation properties of calibration materials and actual patients samples are present—or it may non-systematically affect individual patients samples as well. 

The most important application of the LP measurements is establishing the chemical composition of the ternary compounds. For nitrides, a standard accuracy of X-ray measurements of about 10 ppm would allow us to determine the composition with an error of about 0.1%. Unfortunately, lack of reliable data for elastic parameters of all nitrides and for lattice parameters of AIN and InN leads to a lowering of this accuracy to about 1%. 

Calibration Standards A suitable stock standard [accuracy certified against National Institute of Standards and Technology (NIST) spectrometric standard solutions] may be purchased and used to prepare a Working Standard with a concentration of 100 xg/L. Prepare five calibration standards of 2.0, 5.0, 10.0, 25.0, and 50.0 xg/Lby quantitative dilution of the Working Standard with 2% nitric acid. 

System suitability parameters with their respective acceptance criteria should be a requirement for any method. This will provide an added level of confidence that the correct mobile phase, temperature, flow rate, and column were used and will ensure the system performance (pump and detector). This usually includes (at a minimum) a requirement for injection precision, sensitivity, standard accuracy (if for an assay method), and retention time of the target analyte. Sometimes, a resolution requirement is added for a critical pair, along with criteria for efficiency and tailing factor (especially if a known impurity elutes on the tail of the target analyte). This is added to ensure that the column performance is adequate to achieve the desired separation. 

Quantitative evaluation of thin-layer chromatograms can be performed by direct, in situ visual, and indirect elution techniques. Visual evaluation involves comparison of the sizes and intensities of color or fluorescence between sample and standard zones spotted, developed, and detected on the same layer. The series of standards is chosen to have concentrations or weights that bracket those of the sample zones. After matching a sample with its closest standard, accuracy and precision are improved by respotting a more restricted series of bracketing standards with a separate sample spot between each of two standard zones. Accuracy no greater than 5-10% is possible for trained personnel using visual evaluation. The determination of myco-toxins in food samples is an example of a practical application of visual comparison of fluorescent zones. 

For simple solutions where the composition is known or the matrix can be matched well between samples and standards, accuracy can be better than 2% for analytes at concentrations 50 times the detection limit. For solutions of unknown composition, an accuracy of 5% is typical. 

Precision Standardization (accuracy) Interference Technical performance (automation) Cost Alanine aminopeptidase (AAP) Alkaline phosphatase y-glutamyltransferase (GGT) Maltese Trehalase brush border... 

Table 3.4a. Sedimentological and mineralogical characteristics of some studied samples by SEM, shown in Plate 9 (remark the quantitative mineralogical composition was determined by X-ray diffraction of sample powder and oriented preparation, using mixed multimineral standards accuracy 1-2%)...

Owing to the weU-known high sensitivity of optical emission spectrometry, detection limits reach from 10 g g for metals and C, S, P, B to 10 g g for elements such as H, O, N, considering instantaneous analysis. For quantitative analysis using calibration standards, accuracy 0.2 1 at.%, has been reported for thin layer analysis. For the bulk analysis one has to expect inferior accuracy in the 5—10% range, also for the general case of instantaneous in-depth analysis. 

Accuracy can be evaluated based on a determination of the percent relative error provided that a known value is available. A certified reference standard constitutes such a standard. Accuracy is calculated and reported in terms of a percent relative error according to... 

The surface dilatational modulus (E) and the phase angle (6) were measured as a function of time with constant amplitude (A A/A) of 3% and angular frequency ( ). The range of angular frequencies used was 0.007-0.625 rad/s. The sinusoidal oscillation for surface dilatational measurement was made with 3-5 oscillation cycles followed by a time of 3-5 cycles without any oscillation. The average standard accuracy of the surface pressure is roughly 0.1 mN/m. The reproducibility of the results (for at least two measurements) was better than 0.5%. 

Kawamura et al. [81] have surveyed nonylphenol by GC-MS (with quantification by GC-SIM-MS) in 207 samples of food contact plastics and baby toys. Crompton [43] has described the quantitative GC analysis of residual vinylchloride, butadiene, acrylonitrile, styrene and 2-ethyIhexylacrylate in polymers by solution headspace analysis. Considerably greater sensitivities and shorter analysis times were obtained using the headspace analysis methods than were possible by direct injection of polymer solutions into a GC. Similarly, various residual hydrocarbons (10 ppm of isobutane, n- and isopentane, iso- and neohexane) in expanded PS were determined by GC analysis of a solution of the sample with hydrocarbon internal standards accuracies of 5 to 10% were reported [82]. Residual n- and isopentane (0.001%) in expandable and expanded PS were also determined by a solvent-free procedure consisting of heating the polymer at 240°C in a sealed tube, followed by HS-GC calibration against known blends of n- and isopentane and n-undecane internal standard [82]. 

Pressure transducers were calibrated using a Model SS2170-150 Seegar Transfer gauge (0 to 150 psia) as a secondary pressure standard. Accuracy of this gauge was 0.05 percent of full scale (0,075 psi), but it was calibrated to the precision of the dial (0.05 psi) with a Ruska dead-weight tester. 

Accurate, programmable level alarms are standard. Accuracies of better than 1 mm (1/16 in) over a 40-m (125-ft) range can be attained. 

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