abstract

What: Standard addition is an analytical technique that allows the user to quantitate analytes in complex samples with high background or when surrogate standards are not readily available. The matrix with a background concentration of the target analyte is spiked with increasing amounts of known standard of that analyte and the subsequent standard addition curve and the response factor are used to extrapolate an unknown concentration in the original sample. MultiQuant™ Software is currently unable to perform this technique natively inside the software, it must be accomplished using a query architecture, which can be time consuming and prone to human error.

introduction

How: In this example of pond water screening, background levels of ciprofloxacin were observed in the sample matrix. First, a standard curve was prepared by spiking increasing amounts of known standard of the analyte into the sample matrix. By activating the standard addition feature in the processing method in SCIEX OS Software, the background level was easily calculated, and the calibration curve plotted. To do this you have to:

• Set Sample Type to Standard for all samples including the Blank samples whose concentration is to be calculated
• For the Blank sample, 0 is set in the Actual Concentration column.
• For the spiked matrix solutions, the actual concentration spiked into to the samples is set in the Actual Concentration column
• The column “Standard Addition Calculated Concentration” was activated in the Results Table to show the calculated concentration of the endogenous level of ciprofloxacin in the Blank samples (Figure 1)
• Results are dynamically updated when any changes are made to the Results Table

One of the critical requirements of standard addition is ensuring the correct amount of analyte is spiked in to the matrix aliquots to allow extrapolation back to the background level in the blank matrix. The standard addition feature addresses this issue by plotting a calibration curve of the Added Concentration on the x-axis (Figure 2) and a dotted line indicating the background level in the sample matrix.

Figure 1. Results Table. Standard Addition Calculation Concentration column showing the background concentration of the target analyte in the pond water matrix.

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Figure 2. Standard addition calibration curve in pond water matrix.

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references

References

1. Improving routine quantitation using SCIEX OS-MQ Software. SCIEX technical note RUO-MKT-07-7661-A.