Methods 3510C and 3520C state to spike surrogates into the graduated cylinder or sample bottle and mix well. Multiple transfers introduces potential for losses and mixing well in a graduated cylinder is difficult.
Would it be acceptable to transfer the sample to a separatory funnel for 3510C then add the surrogates? This minimizes the possibility of cross-contamination from the graduated cylinders.
Knowing that it is important to already have solvent in the continuous liquid/liquid extraction (CLLE) body before the addition of the sample or the water will get into the boiling flask, would it be acceptable to add the surrogates to the upper (aqueous) phase in the CLLE?
It would be acceptable to add the surrogate spiking solution directly to the separatory funnel rather than to a graduated cylinder or the sample container. Even though the cylinder and container are solvent rinsed, there is a remote chance a portion of the surrogates could be retained on the glass walls. Should you choose to spike directly into the sample volume in the separatory funnel, be sure to perform this step prior to pH adjustment and the first solvent addition.
It would also be acceptable to set up the sample and methylene chloride in the CLLE and then spike directly into the upper aqueous phase, provided your spike is in a water miscible solvent.
However, since the final decision on whether this change is acceptable will come from your regulatory agency/accrediting body, it would be advisable to contact them first.
Other Category: QA/QC