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The Copper Content of Butter Made by a Continuous Method

1952; Elsevier BV; Volume: 35; Issue: 4 Linguagem: Inglês

10.3168/jds.s0022-0302(52)93704-1

1529-9066

Douglas E. Miller, P.H. Tracy,

Food Chemistry and Fat Analysis

The Cu content of freshly drawn milk has been determined by several investigators.The values reported vary from 0.06 to 0.80 ppm.Differences in technique possibly account for some of the differences in results reported.Some studies (12, 4) have been made of the Cu content of butter but none have been reported on the Cu content of butter made by one of the newer continuous processes developed in this country.It was for the purpose of obtaining such information that this study 3 was made.An attempt also was made to determine whether the Cu is associated with the fat or non-fatty portions of the butter.1ViETttOD OF DETERMINING COPPER Ordinarily colorimetric methods are used for determining the amount of Cu in dairy products.Research workers, however, do not agree on the best method for preparing the sample for analysis (1,3,5,6,8,9,10,11, 13).Conn et al.(2) found sodium diethyldithiocarbamate most desirable as a colorimetrie reagent in the determination of Cu.They state that the sensitivity for the carbamate method is 0.01 ppm.Moir and Andrews (10) also found it desirable.Hetrick and Tracy (7) state that few metals interfere with the carbamate determination and, with the exception of cobalt, nickel and bismuth, these interferences can be eliminated by extraction of the Cu carbamate with carbon tetrachloride from an ammoniacal citrate solution at pH 8.5 to 9.0.These workers also found that if the nickel concentration is equal to the Cu concentration, a high degree of accuracy cannot be had with the carbamate method.The dry ashing method was selected for this study because of its greater simplicity and because of the satisfactory results obtained in a previous investigation made in this laboratory (7). METHODS OF ANALYSISThe apparatus used consisted of 100-ml.pyrex beakers, platinum-tipped tongs, Coleman Universal spectrophotometer, matched pyrex cuvettes, muffle furnace equipped with rheostat and pyrometer, heat lamps, pyrex glassware, 125-ml.pyrex separatory funnels and pyrex still to prepare all distilled water.Distilled water was used for all dilutions.All glassware was cleaned and rinsed with nitric acid, followed with distilled water.All reagents were stored in pyrex containers.The reagents were prepared as follows: