= Mass spectrometry matrix factor
A \b[mass spectrometry matrix factor] compares <analyte> response in a <sample matrix> with response from an equal amount in a specified reference solution. For matched acquisition and blank-corrected peak areas, a common post-preparation comparison is
$$
\mathrm{MF}=\frac{A_{\rm post}}{A_{\rm neat}}.
$$
The post-preparation sample is a prepared blank matrix to which the <analyte> is added after extraction. This separates response from <extraction recovery> under the matching assumptions. MF below 1 indicates <ion suppression> relative to the reference; MF above 1 indicates enhanced response. The number is not an absolute ionization efficiency.
The original method study distinguishes matrix effects, recovery and variation across sample sources.<Strategies for the assessment of matrix effect in quantitative bioanalytical methods based on HPLC-MS MS by B. K. Matuszewski and others>[Abstract, absolute/relative matrix effects and recovery measurements.]{ref} For an invented example, take neat response $1000$, post-preparation response $750$ and response $450$ when the same nominal amount is added before preparation. Then MF is $0.75$, the estimated recovery is $450/750=0.60$, and <mass spectrometry process efficiency> is $450/1000=0.45$. The product $0.75\times0.60=0.45$ identifies which two effects this model combines.
An <internal-standard-normalized matrix factor> divides <analyte> MF by the corresponding MF for an <internal standard>. If both are $0.50$, the normalized value is 1 even though both raw responses are suppressed. If the <analyte> MF is $0.80$ and the standard MF is $0.40$, the normalized value is 2. Normalization can therefore fail when the two responses change differently.
Magnitude and variability are separate questions. Three matrices giving factors $(0.50,0.50,0.50)$ have a large common suppression but no between-matrix variation in this invented set. Factors $(0.50,0.70,0.90)$ differ between matrices despite their less suppressed mean. Report the reference, <analyte> level, sample preparation and response calculation; near-zero reference signals make a ratio unstable, and unmatched volumes or uncorrected offsets can invalidate its interpretation.
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