An analyst performs a LC-HRMS scan of an extract of post-mortem blood. The sample contains fentanyl, which is used to calculate the mass accuracy of the instrument. The exact mass is 336.2202 Da. The analysis produces a measured mass of 336.2189 Da. What is the mass accuracy in ppm?

Question

Quizplus · Accepted Answer

Mass accuracy is calculated by taking the difference between measured mass and exact mass, dividing it by the exact mass, and then multiplying by 1,000,000 to get the measurement in parts per million (ppm). In this case, the calculation would be: 
((336.2189 - 336.2202) / 336.2202) x 1,000,000 = -3.9 ppm. The negative sign indicates that the measured mass was lower than the exact mass. Therefore, the answer is B.

An Analyst Performs a LC-HRMS Scan of an Extract of Post-Mortem