Linearity and precision

Compared with conventional impurities measurements, trace analyses caimot be expected to achieve the same linearity and precision values. This is due to the lower signal-to-noise ratios inevitable at low levels. Hence, while the same approaches can be used, greater latitude will be necessary in the acceptance criteria. What must be demonstrated is that the data is statistically valid to show that the levels of toxic analytes are below their specification limits. 

The industry also has an important need to provide good science to regulatory agencies to support its viewpoint. It is only in cooperation that a reasoned and realistic position can be achieved. 

Genetic Toxicology and Cancer Risk Assessment, Marcel Dekker, New York, 

Lutz and A. Kopp-Schneider, Threshold dose response for tumor induction by genotoxic carcinogens modeled via cell-cycle delay. Toxicological Sciences, 1999,49(1), 110-115. 

Vamvakas, A. Kopp-Schneider, J. Schlatter and H. Stopper, Deviation from additivity in mixture toxicity relevance of nonlinear dose-response relationships and cell line differences in genotoxicity assays with combinations of chemical mutagens and g-radiation. Environmental Health Perspectives Supplements, 2002,110(6), 915-918. 

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In a classic study that illustrates the principles of the method, an XRPD procedure was described for the estimation of the degree of crystallinity in digoxin samples [35]. Crystalline product was obtained commercially, and the amorphous phase was obtained through ballmilling of this substance. Calibration mixtures were prepared as a variety of blends from the 100% crystalline and 0% crystalline materials, and acceptable linearity and precision was obtained in the calibration curve of XRPD intensity vs. actual crystallinity. Figure 7.13 shows the powder pattern of an approximately 40% crystalline material, illustrating how these workers separated out the scattering contributions from the amorphous and crystalline phases. 

HP-jS-CD were added. All compounds were resolved in 20 min (see Figure 5). The data indicated that the validated method offered equivalent and complementary information, in terms of selectivity, sensitivity, accuracy, linearity, and precision, to that of an established gradient LC method employed for similar purposes. Ragaglitazar is a dual peroxisome proliferator-activated receptor ot and y agonist intended to restore insulin sensitivity and correct diabetic dyslipidemia. A chiral CZE method combining two CDs, sulfobutylether-jS-CD and dimethyl-/i-CD, lent itself to the analysis of ragaglitazar, its distomer (the (+)... 

Accuracy Use of an orthogonal technique, spike recovery or inferred once specificity, linearity, and precision established... 

The accuracy of a method is defined as the closeness of the value obtained to known or accepted values. Accuracy can be determined in a number of ways, depending on the nature of the CZE method and availability of orthogonal techniques to compare results. If practical, spike recovery studies (i.e., testing to determine whether recovery matches the amount of a known analyte or impurity spiked) are good alternatives to orthogonal assay comparisons. ICH guidelines also allow method accuracy to be inferred, once specificity, linearity, and precision are established. 

Aqueous solutions for linearity and precision studies were prepared from reagent-grade salts of sodium, potassium, calcium and magnesium (Sigma, USA). 

The mobile phase used for the CZE separations of the trypsin digests was 0.1 M tricine and 0.02 M morpholine adjusted to pH 8.15. The mobile phase composition for the linearity and precision data was 0.01 M tricine, 0.0058 M morpholine, and 0.02 M NaCl adjusted to pH 8.0. The mobile phase buffers used to determine peak shape and electrophoretic mobility vs. pH all contained 0.02 M NaCl and 0.01 M of the buffer (pH 3.0, citrate pH 4.0, formic acid pH 5.0, acetate pH 6.0, MES pH 7.0, MOPS pH 8.0, tricine pH 9.0, borate and pH 10.0, glycine) and were adjusted to the indicated pH with acid or base. The column was rinsed with mobile phase between injections or successively with 0.1 M sodium hydrooxide and mobile phase when the mobile phase composition was changed. 

Capillary electrophoresis has been demonstrated to be useful in monitoring the identity and purity of hGH. CZE is capable of discrimination between hGH and several closely related impurities and degradation products, either as the intact species (previous work) or as the trypsin digests (this work). Thus, it is an important adjunct to conventional methods, such as RP-HPLC of digests or conventional electrophoresis of intact proteins, for the identification of hGH. CZE possesses adequate sensitivity to monitor minor impurities it is comparable to RP-HPLC with respect to linearity and precision. Samples with a volume of at least 10 nanoliters will provide acceptable precision those that contain an internal standard will provide the best precision. The peak area response is linear it is possible to extend linearity by increasing concentration as long as the contribution of the sample and its matrix to field inhomogeneities is minimized. The work shows that CZE has potential to be useful in the quality control of proteins such as hGH. 

Instrument vendors should usually perform IQ and OQ testing during installation of a new instrument. Performance qualification testing is more often performed by laboratory personnel through documenting the accuracy, linearity, and precision of the system under typical operating conditions. 

By means of this CD-enhanced fluorescence method, the authors could determine 11-MeBPHT in spiked human urine samples [23]. The standard addition procedure, based on the addition of a constant volume of the spiked urine sample to solutions of increasing methyl-BPHT concentration, was applied using spectrofluorimetric measurements. The linear calibration curves and standard addition linear plots were parallel, which suggested the absence of matrix interferences in the urine samples and permitted the validation of the method. Good linearity and precision were also obtained for the standard addition plots, with correlation coefficients close to unity. Satisfactory recovery percentage values ranging from 97 to 108% were found in the urine samples for the determination of 11-MeBPHT concentrations at low xg/mL levels. 

For the calculation of the critical (Lc) and the detection (LD) limits the same criteria described for CFSV are used (see page 211). Linearity and precision are evaluated in the concentration ranges typical of 3-MH and 3-MHA in wine. 

Range. The validated range is defined as the interval between the upper and lower concentration of analyte and must be such that it can give acceptable accuracy, linearity and precision. The criterion to determine an accurate concentration is that if the measured value falls between 90% and 110% of the true value in sample it may be acceptable as an accurate result. The validation study should operate the range close to the value in which the validation is being carried out and bearing in mind that the estimated uncertainty holds true. 

In order to validate the feasibility and validity of the method of analysis developed, linearity and precision were assessed as described below. Furthermore, the results obtained with the neutral capillary were compared with those obtained previously by our research group using a fused-silica capillary (50). 

The range of an analytical method is the concentration interval over which the method is acceptable in terms of accuracy, linearity, and precision. 

A very simple procedure to check the linearity and precisions as within-assay (or within-day) and between-assay (or between-day) repeatabilities and also the accuracy at three concentration levels is presented ... 

Linearity is the ability to obtain results that are directly or indirectly (by well-defined mathematical transformation) proportional to the concentration of an analyte in a sample within a given range. The range is the interval between the upper and the lower levels of the analytical method that have been demonstrated to obtain acceptable accuracy, linearity, and precision. Hence, the following parameters are typically evaluated during linearity experiments. 

Resistance thermometers, which usually employ platinum elements, have very high sensitivity, linearity and precision. They can be used safely up to temperatures of 500 C, however, one should consider that they are sensitive to neutron and gamma radiation, and in general they have larger time constant then thermocouples, so this must be taken into account when they are employed in the reactor protection system. 

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