SOFT 2004 Meeting Abstracts - Society of Forensic Toxicologists

A71
USE OF STANDARD ADDITION/STANDARD DILUTION FOR QUANTITATION OF
TOXICANTS IN UNUSUAL MATRICES
Erica Horak', Robert Middleberg, National Medical Services, Willow Grove, PA 19090
At the core of forensic toxicology is the desire to quantitate toxicants from a vast array of biological
matrices. Often a forensic case involves unusual matrices, including decomposed or embalmed tissues,
which present complexity to the sample preparation and analysis. Analyte recovery can be variable in these
types of samples; therefore, alternate approaches to quantitation must be considered. One approach taken is
to construct a matrix matched calibration curve. However, blank matrix is often not readily available, and
particularly by the very nature of embalmed or decomposed tissues, a true matrix match does not exist.
Furthermore, recoveries from the blank matrix and actual case samples may still differ. The standard
addition/standard dilution (SASD) technique, on the other hand, accounts for variable percent recovery,
matrix effects, and loss of sample, while the sample itself serves as its own quality control. The SASD
technique can take any of several approaches. The simplest approach involves establishing a relationship
between the responses of the analyte in the native sample (blank) with the response of the native sample
with a known analyte concentration added (spike), without consideration of an internal standard in the
event one is not available. A second approach includes the use of an internal standard, ideally an isotopic
analog of the analyte, and establishing the relationship between the response ratios of both the blank and
the spike (at one or more concentrations). In a third approach, the native sample is divided into four
aliquots. One aliquot is left untreated and the others are either spiked with various analyte amounts or
diluted. Each sample is then assayed through the analytical method. A plot of the response ratio data
versus the amount of analyte added yields a line such that the extrapolated negative x-intercept is the
concentration of the analyte in the native sample. In a final approach, three measurements can be made:
that of the blank, the blank spiked at one or more analyte concentration, and the blank diluted by some
factor. The use of a derived formula relates the relative responses, and spiked addition and dilution
amounts, to the concentration of analyte in the native sample. In this presentation, the method of standard
addition/standard dilution as an ideal approach to quantitation of drugs in complex and unusual matrix
types will be demonstrated from actual forensic case data. Advantages and disadvantages of the technique
will also be discussed.
Keywords: Standard addition; Matrix; Quantitation
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