Blank samples

[Juan Pedro]

Hello,

I am validating methods for quantifying glucose, cholesterol and Triglycerids in blood samples. I can´t find any blank samples in order to measure selectivity or limit of detection, because all human samples have these analytes.

Could you please help me with this?

Thanks!

[krickos]

Hi

Perhaps you can go around that by spiking samples. unless there is syntetic plasma/blood that can be used?

For LOD (from ICH q2R1): Perhaps you can do a standard addition calibration curve on a more diluted sample and use the 2nd option below.

6.3 Based on the Standard Deviation of the Response and the Slope
The detection limit (DL) may be expressed as:
DL =3,3*σ/S

where σ = the standard deviation of the response
S = the slope of the calibration curve
The slope S may be estimated from the calibration curve of the analyte. The estimate of σ may be carried out in a variety of ways, for example:

6.3.1 Based on the Standard Deviation of the Blank
Measurement of the magnitude of analytical background response is performed by analyzing an appropriate number of blank samples and calculating the standard deviation of these responses.

6.3.2 Based on the Calibration Curve
A specific calibration curve should be studied using samples containing an analyte in the range of DL. The residual standard deviation of a regression line or the standard deviation of y-intercepts of regression lines may be used as the standard deviation.

[lmh]

(1) I'm not sure it's safe to estimate the LOD from the sd of the curve a very long way from the LOD.
(2) Unless you occasionally have samples that apparently contain nothing, I really see no meaning in the LOD. Must it be part of your validation?