Matrix enhancement and suppression is frequently observed in modern analytical routines, such as GC, HPLC, and ICP.
Matrix effect is quantitated by the use of the following formula:
where 
A(extract) is the peak area of analyte, when diluted with matrix extract.
A(standard) is the peak area of analyte in the absence of matrix.
The concentration of analyte in both standards should be the same. A matrix effect value close to 100 indicates absence of matrix influence. A matrix effect value of less than 100 indicates suppression, while a value larger than 100 is a sign of matrix enhancement.
An alternative definition of matrix effect utilizes the formula:
The advantages of this definition are that negative values indicates suppression, while positive values are a sign of matrix enhancement. Ideally, a value of 0 is related to the absence of matrix effect.