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采用卡式炉样品处理器相对空白值对水分测定结果的影响KF Application Note K-48QMetrohm Sample preparation with theoven technique- relative blank Large sample sizes can lead to subtraction of too high blank values. ThisApplication Note describes the calculation of a relative blank and thus helps toimprove the accuracy of the method. Relative blank values Generally， samples with water contents in the low ppmrange require large sample sizes. If the sample should beanalyzed using the oven technique， large sample sizescan lead to wrong or even negative results. Onepossible reason for the wrong results can be thesubtraction of too high blank values. Oven technique (885 Compact Oven SampleChanger/899 Coulometer) 2.34 Result with subtraction of blankempty vial Why are the blank values too high? Blank values are determined using empty sample vials. Iffor the sample determination， half of the volume (oreven more) of the vial is filled with sample， the blankvalue determined with the empty vial is too high and toobtain correct results， only half of the blank should besubtracted. Mean (n=10) [ug/g] RSD [%] 20.7 1.45 Result with subtraction of blankrel. For water determinations in large sample sizes， wetherefore recommend calculating with relative blankvalues. Oven technique (874 Oven Sample Processor/851Titrando) Mean (n=10) [ug/g] RSD [%] 14.7 1.91 V vial Mean (n =10) [ug/g] RSD [%]20.7 1.45Result with subtraction of blankrel. Conclusion Examples Water determinations obtained by the oven techniqueshow a too low water content when the blank value ofthe empty vial is subtracted. In contrast， the subtractionof the relative blank value leads to results that agreewith those using direct injection. Volume of vial filled with sample [%] Total blank value subtracted from EP [%] 50 50 60 40 70 30 80 20 Results The following results of water determinations in oilillustrate the influence and the importance of therelative blank. Measurements were performed usingdirect injection and oven technique. Direct injection www.metrohm.com QMetrohm