안녕하세요,

The answer depends on your application. The formulas you described for LOD and LOQ are closely related to guidelines provided by the FDA in the Q2B and should be generally applicable. While it is good practice to include blanks to exclude impurities, this same guideline provides methods to estimate LOD and LOQ from the calibration curve that you ran: (Methods 6.3.2 and 7.3.2).

-James

http://www.fda.gov/downloads/drugs/guidancecomplianceregulatoryinformation/guidances/ucm073384.pdf

Please see the these tutorials regarding LOD & LOQ:

http://view6.workcast.net/?cpak=5804874214564175&pak=1939778377848693

If I'm not mistaken, you used linear regression method

This paper may help you 

Dear Mr De Sotto:

Look in the following link:

http://www.fda.gov/downloads/AnimalVeterinary/GuidanceComplianceEnforcement/GuidanceforIndustry/UCM207942.pdf

There, you can find a detailed information about compute LOD and LOQ.

Regards, and good luck.

Beatriz Soledad

You may find the following link useful:

40 CFR Appendix B to Part 136 - Definition and Procedure for the Determination of the Method Detection Limit

http://www.gpo.gov/fdsys/pkg/CFR-2012-title40-vol24/pdf/CFR-2012-title40-vol24-part136-appB.pdf

Good luck!