Article written by Wade Delong, Lab Manager, Analytical Products Group
Complete article from Edition 34 APG eNewsletter
Historically false positives for benzyl alcohol in the Base/Neutral Extractables have plagued proficiency testing (PT) participants. These false positives occur most often when butyl benzyl phthalate is present and of course when benzyl alcohol is not. The most probable source of the benzyl alcohol is the extraction process for the base neutrals, in which a pH adjustment is necessary to obtain recovery of the full range of compounds. SW-846 Method 3510C and 3520C (sample preparation methods for analytical method 8270C) recommends an initial extraction at pH <2 and a secondary extraction at pH >11, but allows for the reverse. 40CFR part 136 Appendix A Method 625 states the initial extraction is to be performed at pH >11 and the secondary extraction at pH <2.
Phthalates are also known as phthalate esters, and esters are subject to hydrolysis by both acids and bases. Esters remain stable in aqueous solutions until a strong acid or base is added, which laboratories must do to perform the extractions for base-neutral and acid extractables. Esters in the presence of a strong acid and water will form carboxylic acids and alcohols as reaction products. This reaction is reversible; therefore it may be an advantage to perform the initial extraction at the acid pH. Esters undergoing base hydrolysis will produce a carboxylate ion and an alcohol. The base hydrolysis is irreversible due to the properties of the carboxylate ion.
PT study data has shown a direct correlation between the false positives for benzyl alcohol and low recoveries for butyl benzyl phthalate. Taking this into consideration, it is advisable that laboratories monitor the fate of butyl benzyl phthalate when developing Standard Operating Procedures (SOPs) for extraction of base-neutrals and acids. In particular labs should focus on what order the pH adjustment is done and the strength and volume of acids and bases used for the adjustment.
For quality control samples containing butyl benzyl phthalate please contact APG customer service representatives.
|
