Sample analysis
Under optimum conditions, the determination of lactose in the three milk power samples was carried out
according to the procedures described earlier. Typical
electrophorogram of milk powder sample is shown in Fig.
3A. As we can see from Fig. 3A, the electrophorogram
consists of only two peaks, peak b is proved to be the lactose peak either by comparing its migration time with
that of Fig. 3B, or by the standard-addition method.
Peak a in Fig. 3A is the system peak caused by some
high molecular compounds including hydrocarbons and
proteins, which exist in milk powder samples. It is found
that upon hydrolysis the height of peak a reduces signi®cantly, and some new peaks at longer migration time
appear. The assay results of three milk powder samples
are summarized in table 2,which indicate that the assay results of lactose in milk powder samples are consistent
with the labeled amount of the manufactures.