What Are the Standard Addition Columns in a SCIEX OS Software Results Table?

For research use only. Not for use in diagnostic procedures.

Answer

Sciex OS software allows users to process standard addition results by selecting the Standard Addition option in the Components tab of the processing method in the Analytics mode. What do the new standard addition column headers mean?

1) Actual Concentration. The software manual describes this value as the "known concentration of standard added to each sample in the standard addition group." This is not the final concentration of the spiked sample; instead, Actual Concentration refers to the relative concentration added (or spiked) into the unspiked sample. This is the amount to be quantified by standard addition and is also plotted on the x-axis as the Added Concentration in the standard addition calibration curve. (Example: If the unknown sample has x ppb of analyte, then the subsequent standard additions can consist of a series of concentrations of the unspiked sample with no standard added to it (i.e. Actual Conc = 0) and several samples spiked with varying concentrations of the analyte (say 1, 2, 5 and 10 ppb).)

2) Calculated Concentration. The calculated concentration is the calculated value of the amount spiked into the unknown and is derived from the standard curve. Calc Conc = Added Conc 

3) Accuracy and Accuracy Acceptance. Accuracy is calculated from the Calculated Concentration and the Actual Concentration above. Accuracy = [(Calc Conc)/(Actual Conc)] /100%
Accuracy Acceptance (not Standard Addition Accuracy Acceptance) appears in the results table for standard addition, however, we would not expect to have good accuracy in standard addition when comparing what we know was added (actual conc) to what is actually there (calculated conc) because of the residual analyte levels in the sample prior to the addition of the standard. The Calculated Concentration is calculated by interpolating from the standard addition curve based on the peak areas of each spiked sample and is compared against the Actual Concentration to give the values in the Accuracy column. Important to note that the Calculated Concentration value for the unspiked sample is meaningless, because technically there should be nothing to calculate in a sample that does not have any standard added to it and thus, is always set to "N/A" for unspiked sample in a standard addition group.


4) Standard Addition Actual Concentration. The software guide indicates "user-specified expected known concentration for samples". This value is used to calculate the standard addition accuracy, comparing the Standard Addition Calculated Concentration (derived from the linear curve) to the Standard Addition Actual Concentration. Standard Addition Actual Concentration is not the same as the Actual Concentration, but rather the known concentration of a QC sample that is quantified by standard addition. This column is optional and depends on if the user wants to include QC analysis in their standard addition workflow.  Default value for this column is "N/A" for non-QC-type samples like unknown samples.

5) Standard Addition Calculated Concentration. This is the x-intercept concentration that is calculated from the x-intercept of the standard curve. If the user wishes to quantify QC samples by standard addition, they must enter the known concentration of the unspiked QC sample in the Standard Addition Actual Concentration column, which would then be compared against the Standard Addition Calculated Concentration (which is calculated by extrapolating to the x-intercept of the standard addition curve) to give the Standard Addition Accuracy (see image).

It is important to note that the software reports a single value in the Standard Addition Calculated Concentration column for all samples belonging to the same standard addition group (i.e., unspiked + spiked) that corresponds to the unknown concentration in the unspiked sample as there should only be one x-intercept for each standard addition curve. The unspiked QC sample to be quantified by standard addition must still be set to "Standard" sample type in order for the standard addition feature to work, and NOT "Quality Control" sample type.