Precision and Accuracy of the Methods

If the amounts of contaminants in the lignin sample are not negligible, e.g., the carbohydrate and protein contents are each more than 2% of the lignin, then 

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Diclofenac sodium, famotidine and ketorolac were analysed utilising their formation of a coloured charge transfer complex with 2,4 dichloro-6-nitrophenol. The complexes were detected by UV/visible spectrophotometry at 450 nm. The method was not affected by the presence of common excipients in the formulations analysed. The precision and accuracy of the method was comparable to that of HPLC methods used to analyse the same samples. ... 

The selection of a solid sorbent for personal sampling of pesticides was based on the factors of good recovery of the sample, adequate capacity and storage stability, and contribution to overall precision and accuracy of the method as discussed earlier. The sorbent should also be inert and free of background interferences. Prewashing the sorbents before use by Soxhlet extraction with a methanol/acetone solution and drying was done to remove residual monomers, impurities, and any solvents. 

In-day/out-of-day variation Does the precision and accuracy of the method change when conducted numerous times on the same day and repeated on a subsequent day ... 

Alternatively, microextraction with hexane and analysis by GC-ECD precision and accuracy of the method not established. 

Aqueous samples extracted with hexane extract injected onto GC column for ECD detection precision and accuracy of the method found to be low (Wirth and Patnaik, 1993). 

Suggested method adsorbed over coconut charcoal (100 mg/50 mg) desorbed with CS2 and analyzed by GC-FID recommended flow rate 100 mL/min sample volume 10 L precision and accuracy of the method not established. 

Suggested method adsorbed over carbon molecular sieve (-400 mg) in a cartridge heated at 350°C under He purge transferred into a cryogenic trap and flash evaporated onto a capillary column GC/MS recommended flow rate 2 L/min sample volume 100 L precision and accuracy of the method not known. 

There are two basic approaches off-line and on-line. The off-line method, as discussed in the chapters on sample pretreatment, are most often used because they involve either manually or automatically collecting a fraction from a sample cleanup sorbent. The appropriate fraction is transferred and then assayed by a second chromatographic method. The manual steps are time-consuming and potentially introduce significant error to the j precision and accuracy of the method. The on-line method, when fully automated, would have the chromatography system perform sample pre- j treatment by column switching between two or more columns. j... 

The absorbing solutions are analyzed either by specific ion electrode, colorimetry, or titration depending on the analyte of interest. TABLE 2 presents a list of absorbing solutions and method of analysis for a variety of gaseous air contaminants. The overall precision and accuracy of the method depends on calibration, absorption efficiency, interferences present and time duration between collection and analysis. 

The precision and accuracy of the method was assessed by analyzing batches on three occasions (days). Each run included a duplicate set of calibration standards (CS) and a set of quality control samples (5 QC levels in 5 replicates). The following QC levels have been used 1, 3, 100, 800 2500 ng/mL in plasma and 0.25, 0.6, 25.2, 40 and 128 ng/mL in urine. The highest QC level was above the upper limit of quantification (ULQ). These samples were analyzed after 5-fold dilution in human plasma/urine prior to analysis in order to evaluate the possibility of diluting samples with concentrations above ULQ. 

The precision and accuracy of the method was assessed by analyzing batches on three occasions (days). Each ran included a duplicate set of calibration standards (CS) and a set of quality control samples (QC). The following number of QC samples has been analyzed in the three batches ... 

To omit unconventional instrumentation that was not suitable for routine analysis, as proposed by De Graeve et al.88, Bellia et al.81 developed a quite simple method to determine papaverine in blood samples, using conventional flame ionization or a nitrogen-phosphorus detector. The internal standard, strychnine, was added to the sample prior to extraction, which was carried out with toluene after basification, back extraction with acetic acid and extraction of the liberated base with diethyl ether. The gas chromatography was done on a packed column with 2 % 0V-101 at 275°C. To minimize the adsorption effects, the column was silanized by in situ injection and by injection of a concentrated solution of papaverine and the internal standard prior to routine analysis. Precision and accuracy of the method is shown in Table 14.13. 

Spectroscopic determination of atomic species can only be performed on a gaseous medium in which the individual atoms or elementary ions, such as Fe, Mg, or Al, are well separated from one another. Consequently, the first step in all atomic spectroscopic procedures is atomization, a process in which a sample is volatilized and decomposed in such a way as to produce gas-phase atoms and ions. The efficiency and reproducibility of the atomization step can have a large influence on the sensitivity, precision, and accuracy of the method. In short, atomization is a critical step in atomic spectroscopy. 

The purpose of this chapter is to describe in detail the general methods of obtaining complementary experimental and theoretical estimates of negative-ion properties obtained from the ECD and NIMS techniques. The nominal precision and accuracy of the methods are established from random and systematic uncertainties observed in selected results. A listing of the molecular Ea determined by each method will be presented in Chapter 10 and the appendices. 

To check the precision and accuracy of the method, a standard reference material (SRM 8435 whole milk powder) was analyzed. The results of the analysis are presented in Table... 

Unfortunately, the density is a complex function of the exposure time. If the exposure is too short, the contrast of the spectral line to the unexposed portion will be poor if the exposure is too long, the transmission of the line will be too small to measure. The exposure time should therefore be chosen to be between these extremes. The density is also a function of development time, the spectral transition measured, and differences between individual plates. The use of an internal standard substantially improves the precision and accuracy of the method. 

It is important to note that, apart from the correction factors to the amount of reaction (l+f a0)/(l+-Ro/,ic/) the competitive isotopic method involves the determination of the ratio of two isotopic abundances and that absolute measurements of these quantities are avoided. This is the basis of the precision and accuracy of the method, since both mass spectrometric and nuclear radiation methods of determining the relative abundance are orders of magnitude greater than the accuracy of determination of the absolute abundance. 

Table 1, Precision and accuracy of the method (conditions 1.20xl0 M hydrochloric acid, 5.00X10 2M Na202 and 2.00 mL/min flow rate).

The greater portion of a validation exercise is devoted to the establishment of the precision and accuracy of the method. For this discussion, we define terms in accordance with the GUM [15] and VIMS [13], as these documents are the foundation of ISO standards. Figure 4. la lays out their relationships, which differ somewhat from common usage, particularly, with respect to taminology for error [23]. 

Mass spectrometry ICP-MS offers an accurate method for sulfur isotopic ratio measurements and a sensitive technique for elemental sulfur determination. The method may be applied as an absolute method, because the analyzed atoms themselves, and not the radiation they emit, produce the analytical signals. The technique is useful for the analysis of high-purity materials, such as metals and semiconductors. The detection limits obtainable in most cases by ICP-MS are considerably better than typical values reported for ICP-AES. However, the analytical precision and accuracy of the method are often poor. The utility of the method to determine sulfur is further complicated, as efficient ionization of sulfur is difficult to obtain because of the high ionization energy of the element. 

PAA is very similar to NAA in that the photons can completely penetrate most samples. Thus, procedures and calculations are similar to those used in NAA. The method has constraints due to the stability and homogeneity of the photon beam with inherent limitations to the comparator method. Recent developments in bremsstrahlung target technology have improved the photon sources, which greatly benefit the precision and accuracy of the method (Goemer et al. 2001). A detailed discussion of PAA has been given by Kushelevsky (1990). 

A third type of determination for traces of fluoride is based upon reaction with a metal chloranilate. Lanthanum chloranilate has been proposed for this purpose the reagent is added to a solution of the fluoride at pH 4 6 when lanthanum fluoride is precipitated and an equivalent amount of coloured chloranilic acid is liberated measurement of this colour against a blank gives a measure of the fluoride present. Beer s Law is obeyed over the range 2 to 200 //g per ml and the precision and accuracy of the method are said to be of the order of 1 per cent. Phosphate and molybdate both interfere with the method in a quantitative manner. The following procedure has been recommended by Fine and Wynne. 

The literature abounds with assay statistics but perhaps the most statistically interesting publication, based solely on the vast number of samples analyzed, is an epidemiological study of the effects of exposure to secondhand cigarette smoke conducted by the U.S. Center for Disease Control. This assay employed APCI LC/MS/MS for the determination of cotinine, a nicotine metabolite, in semm using a stable isotope internal standard. At the time of the publication, data on >32,000 samples utilizing a single mass spectrometer had been amassed. Precision and accuracy of the method was approximately 6% except at the limit of quantitation (25 pg/mL), which had a C Vof 12%. It is appropriate to point out here that these statistics provide the variation in the entire method. The previous discussion on reproducibility (see Section 13.3.1 and 13.3.2) dealt only with variabihtyhmits imposed by the mass spectrometer based on ion current stability measurements that establish the theoretical limits. 

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