Validation of liquid chromatography mass spectrometry (LC-MS) methods

Self test 9.4

1. An LC-MS/MS analysis method has been developed to measure amount of leucine from blood (elevated levels of this amino acid can indicate pancreatic cancer). The received information about the concentrations of the analyte will be used for research purposes only.

In this research it is important that the results received from the analysis would be with acceptable accuracy at concentration of above a critical level that indicates the presence of the disease. Therefore, accuracy at different concentration levels must be known to estimate LoQ.

Which of the following statements are true:

Precision and trueness should be estimated at different concentrations. LoQ of the method is the concentration at which these parameters are acceptably low. However, if the LoQ of the method is significantly above the critical level of the biomarker then the method should be developed further to lower the LoQ.

LoQ should be found by using the ICH suggested approach where standard deviation of the residuals is divided by the slope of the calibration function and the result is multiplied by 10.

LoQ must be estimated by approach specified by FDA because they regulate the validation of analytical methods used for diagnostics.

2. Precision and trueness of an analysis method that measures imazalil from oranges were estimated at different concentrations:

Concentration (mg/kg)	Relative standard deviation	Recovery
0.01	0.3	0.65
0.05	0.25	0.85
0.1	0.18	0.9
0.5	0.12	0.9
1	0.08	0.9

In this case SANTE/SANCO guidelines must be followed.

Question: What is the LoQ of the method?

Answer:

3. Which of the following statements are true:

LoQ for an approach is estimated that measures glyphosate (widely used pesticide) from soil. Simple water samples with spiked concentration of glyphosate can be used to estimate LoQ of the method.

LoQ of an analysis method is used daily to interpret analysis results. Therefore, LoQ should be estimated regularly and a conservative LoQ estimate should be used.

LoQ can be estimated from calibration data in which lowest calibration level is above the estimated LoQ.

4. Estimate LoQ from given data collected from LC-MS/MS measurements of meropenem (a broad-spectrum antibiotic) from blood. For estimating LoQ use the approach suggested by ICH that uses standard deviation of residuals (LoQ = 10 × stdev(residulas) / slope).

Concentration (mg/kg)	Intensity
0.0005	12053
0.005	104341
0.0101	272494
0.025	676932
0.05	869373
0.103	1894379

For use with ValChrom: st_9.4_1_lod_loq.xls

Notes:

Before estimating LoD use the plot of absolute residuals to estimate which of the highest calibration levels should be removed from data so that the data would be linear. Do not set intercept as zero as in case of these data it is known that the intercept can have a non zero value.

For use with ValChrom delete the lines that do not fit and reupload the CSV file.

Please write result rounded to 2 significant digits (unit: mg/kg).