API Publ 4751:2005 pdf download
API Publ 4751:2005 pdf download.Evaluation of Water Quality Translatorsfor Mercury.
2.2.1 Method 1630
EPA Method 1630 is the main method for quantifying methylmercury in fish tissue and aqueous samples EPA 200la), although it has not yet been promulgated. The specific steps in Method 1630 include: I) distillation to remose the methylmercury from the sample; 2) ethylation to a methylethylmercury form and collection on a graphitic carbon adswbcnt trap; and 3) thermal desorption through a gas chromatography column to separate the mercurs species before reduction to elemental mercury in a decomposition furnace. The elemental mercury is detected using CVAFS. Method 1630 has a method detection limit (Ml)L)of 0,02 ng/L (or ng/g) hut has the ability to detect as low as 0.00’) ng/L.
Also included in this Method is Appendix A for the determination of dimethylmercury. The method for dimethylmercury varies from the original Method 1630 by eliminating the distillation step and purging the entire sample onto the graphitic carbon absorbent trap. The elemental mercury is separated from the dimethylmercury by using gas chromatography. Two mercury peaks. representing the elemental and diinethylmcrcury species, are separated in time and are detected by CVAFS. Appendix A for the determination of dimethylmercury has a MDL of 2 pgL This is a performance based method and actual criteria data are detemiined before and during analysis. Precision is based on replicate analysis of actual samples and has a limit of3l% RSI). Accuracy is detennined using NIST standard,, for OPR and MS/MSD. OPR samples must fall within 67 — 133% and MS/MSD samples between 65 — I 35%. Several studies have been performed citing the Appendix A method that may be eventually used for validation. In the interim. Appendix A is still considered draft. Unlike EPA Method 1630. the method for dimethylmercury does not specifically discLlss how to analyze solids such as fish tissue,
2.22 UW-Madison SOP
The UW-Madison SOP was developed at the University of Wisconsin-Madison (Hurley et al. l9j. It is virtually identical to Method 1634) with the major exception being the distillation of a larger sample volume, resulting in a lower method detection limit. Copper sulfate is added to the distillation to bind sulfates. This method has a method detection limit of 30 pgL for methylmercury. The same laboratories that perform Method 1630 could perform this analysis at a cost of approximately $200 per sample with a tour week reporting time.
2.2.3 USGS Method
Similar to the UW-Madison SOP, the USGS method is virtually identical to Method 1630 with a slightly larger sample volLinse used in the distillation ([)eWild ci al. 2001). Copper sulfate is also added to the distillation to hind sulfides. The USGS method has a MDL of 4() pg/I for methylmercury. The same laboratories that perform Method 1630 could perform this analysis and the cast is approximately $200 per sample with a four week reporting time.
2.3 CLEAN HANDS SAMPLING
EPA Method 1669 covers the sampling and preservation of’ samples using clean hands techniques (EPA l’)96a). Specifically. the method details the procedures for collecting water samples using a two person team, wherein one person becomes the “clean hands” sampler, while the second person, the “dirty hands” sampler. is available to operate equipment and perform tasks where contamination may be presenL Procedures such as preparation of blanks, duplicates, spikes, sample filtration, and preservation are described in this method.
2.4 CONSIDERATIONS IN THE SELECTION OF AN ANALYTICAL METHOD
The selection of a method to test for either K*al mercury or niethylmercury should be based on several factors. including method detection limit, validity of the method, and quality control procedures. These factors determine the quality and usability of the generated data. Without specific quality assurance (QA) criteria, comparison between samples and mains interference may not be possible. Similarly. if QA criteria arc too wide, the results may be highly variable between samples. Tighter QA criteria allow the generation of higher quality data.
The MDI. is determined by the actual method used to analyze mercury. For example. methods using atomic fluorescence have a lower MDL than atomic adsorption for the determination of total mercury. In particular. atomic fluorescence has a broader linear dynamic range and greater sensitivity than atomic adsorption.
In comparison to total mercury methods, methods for methylmercury are still experimental and have not been fully validated by EPA. Indeed, many more studies have been performed on development and validation of total mercury methods compared to methylmercury. due to greater interest by EPA and industry. Methylmercury analysis is typically performed on fish tissue to helter understand hioacccumulaticmn of mercury and determine the partitioning between total mercury and methylmercury.