Matrix Spike
   Matrix effects play an important role in the accuracy and precision of  a  measurement. Sample preparation steps are often sensitive to the matrix.M atrix spikes are used to determine their effect on sample preparation andanalysis. Matrix spiking is done by adding a known quantity of a component that is similar to the analyte but not present in the sample originally.The sample is then analyzed for the presence of the spiked material toevaluate the matrix effects. It is important to be certain that the extraction
recovers most of the analytes, and spike recovery is usually requir ed to beat least 70%. The matrix spike can be used to accept or reject a method. For example, in the analysis of chlorophenol in soil by accelerated solventextra ction followed by GC-MS, deuterated benzene may be used as thematrix spike. The deuterated compound will not be present in the origi nals ample and can easily be identified by GC-MS. At the same time, it haschemical and physical properties that closely match those of the analyte ofinterest.
   Often, the matrix spike cannot be carried out at the same time as thea n alysi s. The spiking is carried out separately on either the same matrix oron one that resembles the samples. In the example above, clean soil canbe spiked with regular chlorophenol and then the recovery is measured.
However, one should be careful in choosing the matrix to be spiked. For instance, it is easy to extract different analytes from sand, but not so ifthe analytes have been sitting in clay soil for many years. The organics inthe soil may provide additional binding for the analytes. Consequently, amatrix spike may be extracted more easily than the analytes in real-worldsamples. The extraction spike may produce quantitative recovery, whereasthe extraction efficiency for real samples may be significantly lower. This isespecially true for matrix-sensitive techniques, such as supercritical extraction.