Analytical Procedures & Quality Control

Reporting Conventions

Analytical 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 routinely reported when organic analyses are performed. Organic contaminants tend to reside in the fatty tissues of animals and so the amount of fat present is an important part of the analyses. Lipids are not reported with metals results unless it is specifically requested. Metals do not tend to reside in the fatty tissue as do organic constituents.

Organic Analysis

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 allow 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 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 lipid (fat) content of each tissue extract is measured. The lipids and other co-extracted contaminants interfere with chemical analysis and must then be removed from the extract. This is typically accomplished by using Gel Permeation/Size Exclusion chromatography (GPC) or open-column chromatography with a material suitable for removing the fats from the analytes of interest. Other chromatography or contaminant removal procedures may be used to prepare the extract for instrumental analysis. We also have a silica-gel column chromatography procedure, which separates the PCBs from the majority of the pesticides. This ensures better identification and quantification of pesticides, which may otherwise coelute with PCBs that are almost always present in fish and birds.

Inorganic Analysis

Tissue sample homogenates are digested with acids prior to analysis. Identification of metal contamination is accomplished by Inductively Coupled Argon Plasma Spectrometry / Mass Spectrometry (ICAP/MS). Mercury content may also be analyzed by Cold Vapor Atomic Absorption (CVAA) techniques.

Quality Control

For each batch of 20 samples or less we analyze a method blank, a lab control spike and if enough sample mass is available a matrix spike and matrix spike duplicate (MS/MSD). For metals analysis we also analyze a certified biological standard reference material (SRM). The control spikes are analyzed on tissue material, typically tuna fish for organics, catfish fillet for metals, and alfalfa for plant analyses.