Relative standard deviation contamination

Lee and Chau [66] have discussed the development and certification of a sediment reference material for total polychlorobiphenyls. Alford Stevens et al. [49] in an inter-laboratory study on the determination of polychlorobiphenyls in environmentally contaminated sediments showed the mean relative standard deviation of measured polychlorobiphenyl concentrations was 34%, despite efforts to eliminate procedural variations. Eganhouse and Gosset [67] have discussed the sources and magnitude of bias associated with the determination of polychlorobiphenyls in environmental sediments. Heilman [30] studied the adsorption and desorption of polychlorobiphenyl on sediments. 

As discussed before, quadrupole based ICP-MS allows multi-element determination at the trace and ultratrace level and/or isotope ratios in aqueous solutions in a few minutes as a routine method with detection limits of elements in the sub pgml-1 range and a precision for determined trace element concentration in the low % range (RSD - relative standard deviation). The precision for isotope ratio measurements varies between 0.1% and 0.5% RSD. This isotope ratio precision is sufficient for a multitude of applications, e.g., for evidence of contamination of sample with depleted or enriched uranium in urine (this technique is used in the author s laboratory in a routine mode14) or the isotope dilution technique for the quantitative determination of trace element and species concentration after doping the sample with enriched isotope spikes. 

The limit of quantitation, as opposed to the limit of detection, is the most important attribute of the swab method because it has been previously determined, from a safety and cross-contamination standpoint, that residual material above the cleaning acceptance limit is of serious concern. The LOQ is defined as a percentage relative standard deviation (percent RSD) of 10%, and the LOD is defined as a percentage RSD... 

Detection limits at or below 1 ppt (1 pg/mL) are routinely attainable for many elements by ICP-MS as long as sources of contamination and reagent purity are carefully controlled. Detection limits as low as 10 ppq (10 fg/mL) are attainable in some cases. A linear dynamic range of up to 108 can be provided by ICP-MS. Short-term precision (relative standard deviation) of 1% to 3% is typical for clean samples. Long-term precision (relative standard deviation) of 5% or better over 8 hours is common for clean samples. Spectral overlaps, discussed previously, can... 

The contribution of the variance of the atomic absorption analysis to the total variance was calculated from duplicate AA analyses of the same extract, usually at the beginning and end of a series of AA measurements of a single metal. The variance of the AA method and the variance of all other factors, including the extraction itself, were calculated and are presented in Table VIII. It can be observed that the contribution to the total variance by the AA measurement is substantial for Cd, Ni, Pb, and Zn. The relative standard deviation from other sources, including the extraction technique itself, contamination, and variation between sup-... 

Although scientists may have an aversion to reporting negative values, these are a direct consequence of the utilization of normal distributions (Figure 6). Consider a contaminant present in a food matrix at 0.1 ppm with a relative standard deviation (RSD) of 100%. 

The CAM exhibited near-instantaneous response, detection limits of0.006 mg/m and median relative standard deviations of 3.1% for vapor levels of 0.01 to 0.25 mg/m. During continuous monitoring of air near the machine, short-lived and elevated concentrations of isopropanol were detected when alcohol-wetted cloths were used to clean the machine after contamination accumulated on particular surfaces, and four places in the machine were identified as sources where nicotine vapors were released into the ambient air. In only a few hours, the sources of nicotine vapors were identified, and this had eluded efforts with traditional methods for months. 

The mean values obtained by both methods show excellent agreement, though for river sites 1 and 2, the values were close to the detection limit of the method. The relative standard deviations are somewhat higher for the method using sample vessels, presumably because losses and contamination have not been completely eliminated. The direct determination gave more precise results, but in this study, satisfactory accuracy was obtained for the total mercury concentration using sample vessels. 

In Tables 4-7, the within-laboratory reproducibility standard deviation (sw), the reproducibility limit (Rw), and the relative standard deviation (RSDw), as well as CV derived from Horwitz equation are given for the contamination levels of 0.1 mg/kg, 0.3 mg/kg, 0.5 mg/kg, and 1.0 mg/kg. The results for sw, Rw and RSDw for each individual trichothecene were calculated from six experiments done in duplicates at the contamination level of 0.1 mg/kg and from ten experiments done in duplicates at the other three contamination levels except those for DON and nivalenol at the concentration levels of 0.3 mg/kg and 1.0 mg/kg which were calculated from nine experiments done in duplicates since one result at each of the two contamination levels was eliminated by the Cochran test. The experimental RSDw values were compared to the CV values derived from Horwitz equation. Majority of experimental RSDw values were lower than reference values, only a few exceeded it. However, they were much lower than upper limits for RSDr given in Regulation (EC) No 401/2006 (European Commission, 2006a) which were 40% for DON and 60% for T-2 and HT-2, thus the determined RSDw are considered acceptable. 

Table 4. Within-laboratory reproducibility of measurements at the contamination level of 0.1 mg/kg, expressed with the standard deviation (sw), reproducibility limit (Rw) and relative standard deviation (RSDw).

ABEI) as the signal-producing compound was constructed. The relative standard deviation was 3.8 % at 0.2 ng mL (n = 7). A detection limit of 0.007 ng mL was obtained with the designed sensor. The proposed analytical method has been applied to measure OTA in naturally contaminated wheat samples [118]. ECL detection with CE separation system was used for the rapid analysis of nicotine in urine and cigarette samples [119], and pseudolycorine in the bulb of lycoris radiata (based on ultrasonic-assisted extraction) [120]. 

Hydrocarbon contamination from oil, grease, and other sources in drinking water and waste-water is determined quantitatively by extraction of the hydrocarbons and measurement of the CH stretching band. The water is extracted with trichlorotrifluoroethane or other suitable solvent, the IR spectrum of the extracted solution is obtained, and the absorbance is measured at 2930 cm- after a baseline is drawn as described earlier. A series of standards of known oil diluted in the same solvent is prepared as the external calibration curve. The method can measure as little as 0.2 g oil/L of water, with a precision of about 10% relative standard deviation (RSD). Precisions of 5%-10% RSD are typical for IR measurements. The entire method can be found in Standard Methods for the Examination of Water and Wastewater, listed in the bibliography. 

Analysis of filtered Baltic Sea samples of about 0.5 pmol/L spiked to nominally I, 2 and 3/tmol/L ammonia and analysed in three independent analytical runs resulted in a mean standard deviation of 0.092 pmol/L or 2.7 % Hansen and Johannsen, unpublished). Similar results have been reported by Riley et al. (1972) and Solorzano (1969). The recent ICES intercomparison exercise (Aminot and Kirkwood, 1995) showed an overall relative standard deviation of more than 20 %, indicating that, despite good precision of ammonia measurements within one laboratory, the inter-laboratory precision is comparatively poor. This is probably due to the ease of contamination in preparations of zero water and standards as well as in the handling of samples for ammonia determinations. 

Is top value the same as good analytics A lot of us are probably of the opinion that the proportions are doubtful if someone drives a Ferrari for 500 m from home to work place everyday or if a private modem baseball stadium is only used twice a year only because of a lack of time. In the same way, a critical discussion of top values/top performance is advisable in analytics is it meaningful to equip the instruments for quality control with DADs only for the reason of image or the like, if de facto these facilities will be used at only 20% capacity, if at all Is the requirement R > 2 meaningful Is it necessary to strive for optimal resolution in every case, or can it sometimes be better just to aim for resolution that is adequate for the analytical problem at hand How many out-of-spec situations do I produce for my colleagues in quality control, if as method developer I claim a relative standard deviation of 0.8% for a method with a biological matrix or a contaminated process sample ... 

The recovery percentage was 93.27 % with a relative standard deviation of 21.8 % at 1.04 x 10 mol dm level (n = 11). The LOD for a signal to noise ratio of 3 1 was about 6 ppb and the limit of quantification (LOQ) was about 50 ppb. The pondered relative standard deviation of 9.5 % was calculated for the ASSWV method. Results found for CER contamination level in extracts through the electroanalytical method were in reasonable agreement with those values determined by using HPLC measurements. 

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