The falling drop method for deuterium oxide: Factors influencing accuracy |
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Authors: | Miriam F Clarke |
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Institution: | Department of Biochemistry, Woman''s Medical College of Pennsylvania, Philadelphia, Pennsylvania 19129 USA |
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Abstract: | Factors affecting the accuracy of the falling drop method for D2O were considered: selection of temperature of the constant-temperature bath, permissible temperature fluctuations, and D2O concentration. Bath temperatures used, 27.24 to 27.32°, and constancy within ±0.002° had no influence on the regression relating drop velocity to concentration, v = a + bc, or sampling error (S.D.v). The latter increases significantly with concentration from 0.05 to 0.23 ml % D2O, is significantly smaller than experimental error (S.D.e), and is inappropriate for estimating intra-assay limits. More appropriate is the S.D.c derived from the variance of the terms of the regression equation. Assay results using this error term can be expected to vary from about ±4.8% at 0.05 ml % to about ±2% at 0.23 ml %. These results compare favorably with those reported for the mass spectrograph used to determine the mass ratio of vapor. A more conservative estimate is obtained by using , which in this work indicated within-assay variability of ±12.4% at 0.05 ml % and ±2.7% at 0.23 ml % D2O. The term S.D.e, corresponding to 0.0062 ml % in these experiments, provides the best means for assay comparisons.Satisfactory recoveries of D2O added to urine averaging 99% of known values were obtained after shell-freezing, without distillation of standards and without permanganate oxidation of samples. No increase in error beyond that anticipated from standards alone was observed when urine was the vehicle. |
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