A close look at Table II, note 2, is informative!  Although note #2 has changed slightly since the 2007 MUR, a Grab sample still MUST be preserved within 15 minutes (unless, like for metals samples, there is another note allowing some other practice).  A COMP must also be preserved within 15 minutes of the end of the composite period!  This leads me to realize that a composite sample for Ammonia testing MUST be preserved with H2SO4 within the aforesaid 15 minute period!  The Standard Method allowance of letting you test within the first 24 hours without adding the acid preservative is "trumped" by the CFR's!  Does this sound correct?  What do you think?