ASTM E203 test method for water using volumetric Karl Fischer titration
13. Report
13.1 Report the percentage of water to the nearest 0.001 %.
14. Precision and Bias
14.1 Sensitivity, precision, and bias depend on several factors, for example, concentration of the KF reagent, titration technique, apparatus, quantity of water titrated, and nature of material being analyzed.
14.2 When using pyridine-based reagents, sensitivity is less than 0.02 mg of water when measurements are made using the amperometric endpoint.
14.3 The following (see Note 18) is an example of the precision attained at an interlaboratory study for determining water with pyridine-based reagents on two samples of acetone containing 0.1 % and 0.4 % water and two samples of methyl ethyl ketone containing 0.05 % and 0.17 % water.
14.3.1 Repeatability (Single Analyst) - The 95 % for the difference between two runs is 0.008 %.
14.3.2 Laboratory Precision (Within-Laboratory, Between-Days, Variability), formerly called repeatability - The 95 % limit for the difference between two averages of duplicates by the same analyst obtained on different days is 0.015 %.
14.3.3 Reproducibility (Multiple Laboratory) - The 95 % limit for the difference between two results (each the average of duplicates) obtained by analysts in different laboratories is 0.027 % absolute.
NOTE 18 - The interlaboratory study was carried out by ASTM Committee D01 on Paint, Varnish, Lacquer, and Related Products, Subcommittee D01.35 on Solvents, Plasticizers, and Chemical Intermediates. Seven laboratories participated, with a single analyst performing duplicate determinations on each of two days, using two methods on the four samples described above. Test Method D1364 was the subject of the test program being compared with each laboratory's own version of a KF method. As neither the means nor the variances of the two sets of data proved significantly different, all of the results were pooled to give estimates of the repeatability based on 55 df and reproducibility based on 47 df. Practice E 180 was used to develop the precision estimates.
14.4 The following is an example of the precision attained in an interlaboratory study for determining water with pyridine-free reagents on one sample each of n-butyl acetate and methyl amyl ketone (see Note 19).
14.4.1 Repeatability (Single Analyst) - The standard deviation for a single determination has been estimated to be 0.0034 % absolute at 40 df. The 95 % limit for the difference between two such runs is 0.010 % absolute.
14.4.2 Laboratory Precision (Within-Laboratory, Between-Days Variability), formerly called repeatability - The standard deviation of results (each the average of duplicates), obtained by the same analyst on different days, has been estimated to be 0.0050 % absolute at 20 df. The 95 % limit for the difference between two such averages is 0.014 % absolute.
14.4.3 Reproducibility (Multilaboratory) - The standard deviation of results (each the average of duplicates), obtained by analysts in different laboratories has been estimated to be 0.0277 % absolute at 8 df. The 95 % limit for the difference between two such averages 0.078 % absolute.
NOTE 19 - The above precision estimates are based on an interlaboratory study of analyses performed in 1994 on a sample of n-butyl acetate containing approximately 0.096 % water and a sample of methyl amyl ketone containing approximately 0.066 % water. One analyst in each of 12 laboratories performed duplicate determinations on the n-butyl acetate sample and repeated one day later, for a total of 48 determinations. The methyl amyl ketone sample was analyzed in a similar manner except 11 laboratories participated for a total of 44 determinations. The analysts were not restricted to any particular instrumentation, titrant, or solvent system. Practice E 180 was used in developing these precision estimates.
14.5 Bias - Because of the wide scope of this test method and varying degrees of interferences, it is impractical to estimate the bias of this test method.
15. Keywords
15.1 free water; Karl Fischer reagent; pyridine-free; volumetric; water; water of hydration
