Low voltage AC-DC transfer standards at LNE
This paper describes the method used to establish the traceability of LNE AC-DC transfer standards in the mV-range to the 1 V multijunction converter, which serves as the primary AC-DC standard. Main uncertainty components are listed and final uncertainty given for the different voltage levels. An independent method was developed for the calibration of thermal converters at 0.3 V and 0.2 V. The agreement between this method and the step-down is within the standard uncertainty.
Automated comparator for accurate AC-DC difference measurements at the BNM-LCIE
This paper describes the new automated comparator system developed at the BNM-LCIE for the calibration of voltage thermal converters used as national AC-DC transfer standards. The system achieves Type A standard uncertainties of a few parts in 10/sup 7/ in the frequency range from 10 Hz to 1 MHz (100 kHz for voltages above 100 V). Type B standard uncertainties, depending on the type of converters to be compared and on the measurement voltage level, are between a few parts in 10/sup 7/ and a few parts in 10/sup 6/.
On the fractionation of β-lactoglobulin and α-lactalbumin
Abstract Existing methods for the preparation of α-lactalbumin and β-lactoglobulin are examined critically. It is proposed that the most satisfactory method for the preparation of the whey protein fraction from bovine milk is (NH 4 ) 2 SO 4 fractionation. A number of new gentle procedures for the fractionation of the whey proteins are compared with some existing methods. The distribution of total protein at various stages is determined by total Kjeldahl nitrogen and the kind of protein by starch-gel electrophoresis. The effect of variables, such as pH, salt concentration and temperature on the separation of α-lactalbumin and serum albumin from β-lactoglobulin is studied. Differences in the behavior ( e.g. solubility) of genetic variants of β-lactoglobulin are noted. The solubility of each of the major whey proteins, under similar conditions to those used in the fractionation, is compared with its solubility in the whey protein mixture. The understanding gained of factors important in the fractionation is used in recommending new procedures for α-lactalbumin and β-lactoglobulin isolation.