= Sample matrix
A \b[sample matrix] consists of the components of an analytical sample other than the <analyte> being measured. The definition is relative to the analytical question: a constituent can be the <analyte> in one measurement and part of the matrix in another.<Sample matrix in IUPAC Gold Book>[M03758, matrix in analysis.]{ref} The <sample matrix> is material, whereas an <analytical matrix effect> is its influence on the measurement.
For an invented composition, a sample contains $90\,\mathrm{mg}$ of <water>, $8\,\mathrm{mg}$ of <glucose> and $2\,\mathrm{mg}$ of <sodium chloride>. If glucose is the <analyte>, the remaining $92\,\mathrm{mg}$ supplies the <sample matrix>. If water is the <analyte> instead, glucose becomes a matrix constituent. Calling something a matrix component does not imply that it is chemically unimportant or present only in traces.
Sample preparation can change the relevant matrix. Extraction, dilution or addition of a reagent changes which constituents reach the detector and in what proportions. An <extraction recovery> measurement asks how much <analyte> survives a specified preparation stage; a <mass spectrometry matrix effect> asks how accompanying constituents change response. Matching only the starting sample type does not establish that final extracts have identical measurement behavior.
A <MALDI matrix> is a deliberately introduced material with a specific role in laser-assisted ion production. It can contribute to the final sample environment, but its name is not a general synonym for all non-analyte constituents. Nor does the word matrix here mean a mathematical array.
An <analytical blank> and a matched <sample matrix> answer different questions. A blank can estimate a background contribution, yet fail to reproduce a sample-dependent change in sensitivity. <Matrix-matched calibration> consequently tries to reproduce relevant measurement conditions as well as the absence or presence of the <analyte>; the label alone does not prove a match.
Back to article page
