Average analytical value

Comments The SEE can be determined by using a single sample analyzed in replicate by one or more laboratories. The average analytical value for the replicates on a single sample is determined as... 

Accuracy (systematic error or bias) expresses the closeness of the measured value to the true or actual value. Accuracy is usually expressed as the percentage recovery of added analyte. Acceptable average analyte recovery for determinative procedures is 80-110% for a tolerance of > 100 p-g kg and 60-110% is acceptable for a tolerance of < 100 p-g kg Correction factors are not allowed. Methods utilizing internal standards may have lower analyte absolute recovery values. Internal standard suitability needs to be verified by showing that the extraction efficiencies and response factors of the internal standard are similar to those of the analyte over the entire concentration range. The analyst should be aware that in residue analysis the recovery of the fortified marker residue from the control matrix might not be similar to the recovery from an incurred marker residue. 

The Student s (W.S. Gossett) /-lest is useful for comparisons of the means and standard deviations of different analytical test methods. Descriptions of the theory and use of this statistic are readily available in standard statistical texts including those in the references [1-6]. Use of this test will indicate whether the differences between a set of measurement and the true (known) value for those measurements is statistically meaningful. For Table 36-1 a comparison of METHOD B test results for each of the locations is compared to the known spiked analyte value for each sample. This statistical test indicates that METHOD B results are lower than the known analyte values for Sample No. 5 (Lab 1 and Lab 2), and Sample No. 6 (Lab 1). METHOD B reported value is higher for Sample No. 6 (Lab 2). Average results for this test indicate that METHOD B may result in analytical values trending lower than actual values. 

For Table 36-2, a comparison of METHOD A results for each of the locations is made to the known spiked analyte value for each sample. This statistical test indicates that METHOD A results are lower than the known analyte values for Sample Nos. 4-6 for both Lab 1 and Lab 2. Average results for this test indicate that METHOD A is consistently lower than actual values. 

So if we take 385 measurements we conclude with a 95% confidence that the true analyte value (mean value) will be between the average of the 385 results (x) 0.1. 

Analytical values for the eight coals after treatment with 2 M HN03 are given in Table III. The reported values are the averages of four determinations (duplicate determinations on different days). A comparison of the dry ash values for the HNOj-extracted residues described in Table III to the dry ash values for the raw coals described in Table I reflects the reduction in mineral matter caused by extraction of the raw coals with 2 M HN03. Carbonates, sulfates, and other minerals dissolve in the acid solution used to extract pyrite. 

The yield is about 90%. The analytical values shown in Table I are average values from several determinations, usually from separate preparations. 

Calculation of Down syndrome risk requires that the distribution of analyte values for all tests in both unaffected and affected pregnancies be known. These distributions are well defined for AFP, uEs, CG, and DIA in singleton pregnancies, and thus reliable risks can be calculated. The distributions of these analytes also are available for twin pregnancy unaffected by Down syndrome the average MoMs in unaffected twin pregnancy for AFP, uEs, CG, and DIA are about 2.0,1.7, 1.9, and 2.0, respectively.Fewer data are available for concentrations of these analytes in twin pregnancies affected with Down syndrome. A fiirther complication is that in... 

The average cmitent of phosphates varied in some years from 1.0 to 4.2 mg m and, in some cases, dropped even to analytical zero. During the whole observation period their maximum content was registered in August 1949 in the southeastern part of the sea - over 20 mg m [8]. The Small Sea was one of the areas with the higher phosphate content (1.0-4.6 mg m as well as the mouth areas of the Amudaiya and Syrdarya. The low level of phosphates was recorded in the western area and in the eastern shallow part of the sea - from 0 to 1.0 mg m . The highest values of phosphate content were usually observed in the surface layer, but with depth it sometimes dropped even to analytical zero (at 10-20 m depths). Some enrichment of the surface water layer with phosphates occurred, thanks to the river flow. The seasonal variations in the phosphate content in the Aral Sea, unlike other seas, were revealed rather weakly. On a year-to-year scale the average phosphate values increased in the water abundant years and dropped with the decrease of flow from the rivers. 

The Nagler and Kramers (1998) eNd mantle evolution curve shows two important features. First, that in the early Archaean the average Nd value is almost constant and about 1.0. Thereafter, from about 3.0 Ga to the present, Nd values steadily increase to a present-day value of +10. Nagler and Kramers (1998) suggest that the average Nd value of about 1.0 for the early Archaean has no geological meaning but is in part an analytical artifact and in part the result of the uncertainty in Nd measurements on chondrites. 

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