Analytical Procedures & Quality Control results are typically reported on a wet-weight or as-is basis. Correction for moisture content to report on a dry-weight basis may be done if requested.
Lipid percentage, or fat content, is typically requested when organic analyses are performed. Organic contaminants tend to reside in the fatty tissues of animals, because of this, the amount of fat present can be a very important part of the analyses in the utilization of the data. Lipids are not typically requested with metals analyses as metals tend to reside in the muscle tissue rather than fatty tissue.
An aliquot of homogenized tissue sample is mixed in a beaker with anhydrous sodium sulfate to remove some of the moisture from the sample and to allow the solvent to better interact with the tissue. Unlike soils, which can effectively be extracted by ultrasonic disruption of a soil/solvent mixture, tissues require a more exhaustive soxhlet or automated soxhlet extraction. This extraction allows solvent to flow through the tissue/sodium sulfate mixture continuously for a set period of time to remove contaminants of interest.
The lipids and other co-extracted contaminants interfere with the chemical analyses. Various extract cleanups are employed based on the constituents of concern being analyzed. This can includeone or more of the following: Gel Permeation/Size Exclusion chromatography (GPC), Silica Gel, Florisil, or Acid Cleanups. Cleanups ensure better identification and qualification of constituents of concern so that Data Quality Objectives (DQOs) are met.
Tissue sample homogenates are digested with acids prior to analysis. Identification of metal contamination is accomplished by Inductively Coupled Plasma Spectrometry / Mass Spectrometry (ICAP/MS). Mercury content may also be analyzed by Cold Vapor Atomic Absorption (CVAA), Cold Vapor Atomic Flourescence (CVAF), or Direct Mercury Analyzer (DMA) techniques.
For each batch of 20 samples or less we analyze a method blank, and lab control spike are analyzed. If enough sample mass is available a matrix spike and matrix spike duplicate (MS/MSD) are also analyzed. For metals analysis, a certified biological standard reference material (SRM) is also included. All control spikes are prepared in a tissue matrix.