ALS has been active in research and development of procedures for preparation and analyses of sediment, tissue, seawater, and freshwater samples matrices.
All tissue samples are subjected to homogenization before analysis. This preparation ensures representative sub-sampling for each analytical parameter. Conventional solvent extraction techniques such as soxhlet and sonication are usually employed for extracting the samples. Prior to instrumental analysis, extracts are put through Gel Permeation Chromatography (GPC) cleanup and silica gel cleanup. Removal of lipids is of particular concern during the cleanup process. The instrumental analysis is performed using GC/MS operated in SIM mode to maximize sensitivity. In addition to the standard list of PAHs typically analyzed, the associated alkylated homologs are also available.
Crab Tissue Sample Total solids values are derived from freeze-dried tissues. The determination is performed on a pre-homogenized wet sample. The dry solids from the freeze-drying determination are then further homogenized and used for the metals analysis (except mercury) as described in the metals section of this website. Freeze-drying is performed to avoid degradation and associated chemical changes that occur when the sample is dried at elevated temperatures.
To obtain the low level detection limits required when analyzing biological tissues, the pesticide and PCB Aroclor analyses are performed by following EPA Methods 8081 and 8082 with slight modifications to the sample mass, final extract volume, and cleanup procedures. In order to assure representative sub-sampling for each analytical parameter, all tissue samples are subject to homogenization prior to analysis. To accommodate the relatively large sample mass required to reach the low level detection limits, the samples are extracted using a sonication technique. The extracts are put through GPC and Florisil cleanups prior to splitting for PCB Aroclor and pesticide analyses. The pesticide fraction generally goes directly to the GC/ECD for analysis. The PCB Aroclor fraction receives an acid cleanup prior to GC/ECD analysis. Detection limit information is listed in the tables following page 13 of the Marine SOQ. For ultra low-level Aroclor analysis a Large Volume Injector (LVI) system is used in conjunction with GC/ECD.
To obtain the low level detection limits required when analyzing biological tissues, the PCB congener analysis is performed by following EPA Method 8082 with slight modifications to the sample mass, final extract volume, and cleanup procedures. In order to assure representative sub-sampling for each analytical parameter, all tissue samples are subject to homogenization prior to analysis. To accommodate the relatively large sample mass required to reach the low level detection limits, the samples are extracted using a sonication technique. The extracts are subjected to GPC, silica gel, acid, and permanganate cleanups prior to GC/ECD analysis.
Tissue samples are analyzed using solvent extraction, derivatization, and GC/FPD. Samples are dried with muffled, anhydrous sodium sulfate. Following the addition of surrogate compounds (tripropyltin chloride and tripentyltin chloride), tissues are extracted with methylene chloride that contains 0.1% (wt./vol.) tropolone. After solvent exchange into hexane, extracts are derivatized with hexylmagnesium bromide in ether via a Grignard reaction. The Grignard reagent is synthesized by ALS (commercially available reagent is not used due to unacceptable purity). Tissue extracts are cleaned by elution through Florisilâ columns. The extracts are analyzed by GC/FPD with a 610 nm filter. A minimum (10%) of analyte hits are confirmed by a secondary column GC/FPD or GC/MS analysis. All detectable values are confirmed if the samples originated from an uncharacterized site (i.e., no historical data to suggest the likelihood of the presence of organotin).
The digestion procedure for all elements except mercury consists of an acid digestion-oxidation under elevated temperature and pressure in a closed system. The procedure is generally preferred over modifications to conventional EPA soil digestions for several reasons. By freeze-drying the sample and grinding it to a homogenous meal, a representative sample is easily obtained. This is especially significant when analyzing whole-body samples where bone, gristle, and skin are difficult to disperse uniformly throughout the sample. This is also true for portions of bivalve samples that are very difficult to homogenize when wet. Besides helping homogeneity, the absence of water in freeze-drying facilitates the digestion/oxidation of organic material by the oxidants added. Performing the digestion in a closed Teflon vessel under elevated temperature and pressure also increases the completeness of digestion and minimizes loss of target analytes during the procedure (i.e. superior matrix spike recoveries are attained).
For mercury, our laboratory digests a larger aliquot of the wet sample than is typically done for routine analyses of solid and semi-solid materials. This allows representative sub-sampling of tissues. The digestion procedure incorporates similar ratios of digesting/oxidizing reagents as standard EPA procedures. Additional concentrated nitric is added to facilitate the digestion of the high organic content.
The digestates are analyzed using a combination of ICP-MS, ICP-OES, GFAAS, and CVAAS. Selenium is typically analyzed using GFAAS because of uncorrectable isobaric interferences when using ICP-MS. Mercury is analyzed in tissue using standard cold vapor techniques. Our laboratory does perform ultra trace mercury determinations using purge and trap cold vapor atomic fluorescence techniques, but generally does not need the added sensitivity to obtain the required detection limits to meet most project objectives. All other elements are analyzed using ICP-MS or ICP-OES, depending on the required sensitivity.
Analysis is performed by EPA Methods 8280, 8290, and 1613 on biological tissue samples. Special clean-up techniques were developed for dealing with tissue samples verses sediment samples to remove biologically active components that could interfere with the analysis. Instrumental analysis is performed by HRGC/HRMS techniques to meet the one part-per-trillion detection limit often requested for tissue samples.