Hi, Dear All, I got some results of my master thesis (atropine and scopolamine detection in contaminated millet with Datura seeds) with HPLC-MS/MS. Now, I want to calculate LOD and LOQ. I know it is 3 times and 10 times of S/N ratio, respectively. My question is how can I report one exact number for LOD and LOQ. Is it an approximate number?!From which chromatograms can I calculate these numbers?The only way is using a software e.g. MultiQuant to calculate?! I am confused about this.
Thank you for your time in advance. Regards,
Saman
You will initially need to set up proper calibration tables spanning the entire range of the samples. Be sure and include plenty of data points (your sample) at the low levels. Measure and record the data. You want to have plenty of points at the lowest levels to more accurately determine the limits (minimize extrapolating values, instead interpolate as much as possible). After determining the ASTM (or other appropriate spec) baseline noise levels, you may either calculate the values by hand, using the chromatograms which contain the appropriate sample data integration height/area values OR you may use the chromatography software (if setup correctly) to determine them.
A minor point after bill. You can get the peak heights at low levels easily. If you want to determine the baseline noise by hand. You need to collect data of a stable baseline in a blank sample run. The time slot should be 10-20 times of your peak width. The STDEV of the baseline using Excel can be calculated as the noise level.
Apologies as I wanted to include the following technical note (not written by me) which I have found useful in presentations over the years for questions of this type. It addresses signal to noise ratio determination in LC/MS systems which is a critical part of solving LOD questions.
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