In
chemical analysis
Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separati ...
, matrix refers to the components of a
sample
Sample or samples may refer to:
Base meaning
* Sample (statistics), a subset of a population – complete data set
* Sample (signal), a digital discrete sample of a continuous analog signal
* Sample (material), a specimen or small quantity of s ...
other than the
analyte of interest. The matrix can have a considerable effect on the way the analysis is conducted and the quality of the results are obtained; such effects are called matrix effects.
[F. W. Fifield, P. J. Haines. ''Environmental Analytical Chemistry''. Blackwell Publishing, 2000, p. 4-5. .] For example, the
ionic strength
The ionic strength of a solution is a measure of the concentration of ions in that solution. Ionic compounds, when dissolved in water, dissociate into ions. The total electrolyte concentration in solution will affect important properties such as ...
of the solution can have an effect on the activity coefficients of the analytes.
[Harris, D. C. ''Quantitative Chemical Analysis'', 4th ed. Freeman, 1995, pp.194, 404. .] The most common approach for accounting for matrix effects is to build a
calibration curve
In analytical chemistry, a calibration curve, also known as a standard curve, is a general method for determining the concentration of a substance in an unknown sample by comparing the unknown to a set of standard samples of known concentration. ...
using standard samples with known analyte concentration and which try to approximate the matrix of the sample as much as possible.
This is especially important for solid samples where there is a strong matrix influence.
[Marco Aurelio Zezzi Arruda. ''Trends in Sample Preparation''. Nova Publishers, 2006, p. 15-18. .] In cases with complex or unknown matrices, the
standard addition method
The method of standard addition is a type of quantitative analysis approach often used in analytical chemistry whereby the standard is added directly to the aliquots of analyzed sample. This method is used in situations where sample matrix also ...
can be used.
In this technique, the response of the sample is measured and recorded, for example, using an
electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...
selective for the analyte. Then, a small volume of
standard solution In analytical chemistry, a standard solution is a solution containing a precisely known concentration of an element or a substance. A known mass of solute is dissolved to make a specific volume. It is prepared using a standard substance, such as a p ...
is added and the response is measured again. Ideally, the standard addition should increase the analyte concentration by a factor of 1.5 to 3, and several additions should be averaged. The volume of standard solution should be small enough to disturb the matrix as little as possible.
Matrix effect
Matrix enhancement and suppression is frequently observed in modern analytical routines, such as
GC,
HPLC
High-performance liquid chromatography (HPLC), formerly referred to as high-pressure liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify each component in a mixture. It relies on pumps to pa ...
, 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.
Matrix effect close to 100 indicate absence of matrix influence.
Matrix effect value of less than 100 indicates suppression, while larger than 100 is a sign of matrix enhancement.
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, value of 0 is related to the absence of matrix effect.
See also
*
Extraction (chemistry)
References
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Analytical chemistry