[id86]

Hi,

I have a question regarding LOD. I am using 10 replicate injections of blank in HPLC to calculate LOD. i am having a problem with one data set (analyte 1) and wondered if anyone can spot where ive gone wrong.

I am trying to calculate LOD for 4 analytes. I have a linear calibration curve for the analytes and the data are as follows:

1: m =548.68  c = +5075.8
2: m= 6444.8  c= -23684
3: m= 229047  c= -785
4: m= 213384  c= -1913.1

So far i have manually evaluated the blank baseline noise and taken the difference of the highest and lowest peaks from a pre-selected interval for all blanks.

Then for each of the analytes i have done the following:

For each of the blank values i used (y-c)/m to give me a series of concentrations that would equate to the blank values. I took the standard deviation of the concentrations and then LOD = mean of the concentraions of the analyte + 3*SD.

Analytes 2-4 seem to be ok however I have ended up with a negative value for the LOD for analte 1. Is my method wrong or can anyone spot an error?

I hope this makes sense

Thank you