What are the instruments you have? If you have a microwave digestion, that is easy. refer the application note. You will not need to use Percholoric etc. In generally nitric or nitric, H2O2 combination will enough.

I agree that perchloric acid is overkill and not necessary.  We use a hotblock method using nitric and H202.  For approximately 1g of sample (any biological tissue sample including milk): 

Add 5 ml of concentrated HNO3. Reflux for 1.5- 2 hours at 92-95 C without boiling or drying.

Check the sample digestion status: If the sample is not totally digested, add another 3ml HNO3 or more until the samples all dissolved in the acid.

Cool sample and add 2ml DI water and 3 ml of trace grade H2O2 , heat sample on the hot block until effervescence subsides.

Cool the sample and bring up the final volume to 50ml with DI water. Gravity filter the samples through acid wash filter paper (Whatman#41) if needed.

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you can use 60 c  add Nitric acid  and Perchloric acid

please look for attach file 

The milk sample need to be brought into clear solution for analysis by atomic absorption spectroscopy. For this reason the sample first digested to dissolve the sample and to remove the fat. 5 gr of raw cow's milk is treated with 5 ml (65% nitric acid) and 2 ml (30% hydrogen peroxide) and then digested on electric hot plate at 90ºC and the temperature of this mixture was gradually increased to 120ºC. Until brown fumes appeared, indicating completion of oxidation of organic matter. The organic matrix of milk was destroyed and left the elements into clear solution, after cooling the clear solution was filtered in to 25 mL volumetric flask and completed to the mark with double distillated water, and a blank digestion solution was made for comparison, finally the milk samples is directly analyzed by GFAAS