Every analyst will encounter source water matrices that consistently result in low matrix spike recoveries and/or debris carryover that interferes with examination of the sample. It is important to learn and practice a variety of techniques to use with difficult matrices.
Always practice and test the technique prior to use on field samples. Performing the appropriate QC validates the use of the modification. Use the IMS Guidance Document and Section 13.3.4 of Method 1623 as guidance as well as discussions with other analysts.