Blank correction omitted

Blank Correction Omitted. There are two common situa-... 

A reagent blank corrects the measured signal for signals due to reagents other than the sample that are used in an analysis. The most common reagent blank is prepared by omitting the sample. When a simple reagent blank does not compensate for all constant sources of determinate error, other types of blanks, such as the total Youden blank, can be used. 

Running a blank determination. This consists in carrying out a separate determination, the sample being omitted, under exactly the same experimental conditions as are employed in the actual analysis of the sample. The object is to find out the effect of the impurities introduced through the reagents and vessels, or to determine the excess of standard solution necessary to establish the end-point under the conditions met with in the titration of the unknown sample. A large blank correction is undesirable, because the exact value then becomes uncertain and the precision of the analysis is reduced. 

The oxidizing solution causes a salt effect which must be compensated for. Aliquots of 25 mL of the blanks and standards are oxidized and treated exactly the same as the samples, or 5 mL of the CSS solution is added to 25 mL blanks and standards, omitting the oxidation step. The salt effect due to sahnity differences between samples and standards is corrected as described for the determination of silicate (see Section 10.2.11). 

All samples should be analysed in duplicate. Blanks are treated in the same way except that the addition of periodic acid and sodium arsenite is omitted. Instead, a 1 h- 1 mixture of both reagents is added, which has been allowed to react for at least 10 min. A correction can thus be made for aldehyde and serine contaminations in the reagents. The blanks are further treated as described above. 

Correct the blank, calibration, and sample runs for initial offset from zero by subtracting from each time interval the average area of the first five time intervals in the corresponding run. Omit from the average any readings (extraneous peaks) that are more than three times the noise as defined in 8.2. 

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