I suggest using US EPA ...

I suggest using US EPA methods for a reference SW-846

Lauren,

Probably your easiest place to learn about analytical and preservation techniques is the on-line references to EPA's Solid Waste Method (includes water). http://www.epa.gov/wastes/hazard/testmethods/sw846/online/index.htm.

Your assessment on containers is correct.  Almost any plastic is going to be fine.  I generally use HDPE because of regulatory compliance and shipping durability issues but have had no issues analytically with polypropylene.  Poly carbonate centrifuge tubes also work well, and are very inexpensive.  Perfect for research.

For trace metals analysis on ICP-MS I suggest that you only use nitric acid, and make sure its trace metal grade or distill your own.  That applies for container washing too.  Don't use HCl for preservation or container washing using ICP-MS.  There are some papers out there that use 6M HCl to preserve arsenic species, but they don't use ICP-MS, and you are looking at total arsenic.  Chloride is a problem for arsenic analysis on ICP-MS but a skilled operator is usually able to get good results (ppb As), even with groundwater chloride as high as 100 ppm. 

Cheers and good luck!

Greg