Introduction

This work demonstrates my understanding of using internal standards.

Experiment

A ground crop sample (105.627 g) was extracted in order to analyze Compound X. Prior to extraction, 13C12- Compound X (10.0 μL of a 350 pg/μL solution) was added to the sample as a recovery internal standard. The extract was passed through a silica gel SPE cartridge to remove co-extracted contaminants, and reduced in volume to 0.500 mL. Immediately prior to analysis by LC-MS/MS, D18-Compound X (10.0 μL of a 100 pg/μL solution) was added to the final extract and all standards as a performance internal standard. Standards were prepared in blank matrix.

The following results were provided by the LC-MS/MS operator.

Figure 1: Calibration Curve
Table 1: Peak areas from crop sample extract

Compound X

13C12- Compound X

D18-Compound X

5498

6248

6957

Average 13C12- Compound X peak area relative to performance internal standard peak area from standard solutions used to construct calibration curve = 0.9637

Results

The percent recovery of the 13C12- Compound X in this crop sample

\(\frac{[Peak\ Area]_{^{13}C_{12}-Compound\ X\ pre\ extraction}}{[Peak\ Area]_{D_{18}-Compound\ X\ post\ extractioin}}\ = \frac{6248}{6957} \ = 0.8981\)

\(Recovery_{{^{13}C_{12}-Compound\ X}}\ = \frac{\frac{[Peak\ Area]_{^{13}C_{12}-Compound\ X\ pre\ extraction}}{[Peak\ Area]_{D_{18}-Compound\ X\ post\ extractioin}}}{\frac{[Peak\ Area]_{^{13}C_{12}-Compound\ X\ post\ extraction}}{[Peak\ Area]_{D_{18}-Compound\ X\ post\ extractioin}}}\ = \frac{0.8981}{0.9637}\ =\ 93\%\)

The recovery corrected concentration of Compound X in the crop sample

\(\frac{[Peak\ Area]_{Compound\ X\ post\ extraction}}{[Peak\ Area]_{D_{18}-Compound\ X \ post\ extraction}}\ = 0.8127 \times\ [conc.]_{compound\ X\ post\ extraction}\ + 0.1392\)

\(\frac{5498}{6957}\ = 0.8127 \times\ [conc.]_{compound\ X\ post\ extraction}\ + 0.1392\)

\([conc.]_{compound\ X\ post\ extraction}\ = 0.8011\ pg/\mu L\)

\([recovery\ corrected\ conc.]_{compound\ X\ pre\ extraction}\ =\ \frac{[conc.]_{compound\ X\ post\ extraction}}{Recovery_{{^{13}C_{12}-Compound\ X}}}\)

\([recovery\ corrected\ conc.]_{compound\ X\ pre\ extraction}\ =\ \frac{0.8011\ pg/ \mu L}{93 \%}\ =\ 0.8604\ pg/ \mu L\)

\([recovery\ corrected\ conc.]_{compound\ X\ in\ the\ bean\ sample}\ = \frac{[recovery\ corrected\ conc.]_{compound\ X\ pre\ extraction}\quad \times\quad volume_{solution}}{weight_{sample}}\)

\([recovery\ corrected\ conc.]_{compound\ X\ in\ the\ bean\ sample}\ = \frac{0.8604\ pg/\mu L\quad \times\quad 0.500\ mL}{105.627\ g}\ =\ 4.07\ pg/g\)

\([recovery\ corrected\ conc.]_{compound\ X\ in\ the\ bean\ sample}\ =\ 4.07\ pg/g\ =\ 4.07\ ng/kg\ =\ 0.004\ \mu g/kg\)

Created Date: 2023-01-23

Last Modified Date: 2023-01-23