Quantification problems

[angupa]

I'm trying to validate a method to quantify enrofloxacin in a pharmaceutical preparation. When I'm doing the repetibility chapter, the
number of replicates obtained are more than five. I'm trying to change the range of calibration curve but the problem persists.
I'm a little bit desesperate with this method.
Is there anybody working with this drug?
Has anybody had a similar problem during validation procedure?

Tanks

[Narendra]

Dear Angupa,

Can you tell us in detailed what problem persists ? I am not able to understand what you want to say ?

Narendra

[angupa]

In the repetibility chapter I'm using a Camacho et al, 1993 formula based that relates the CV with the number of replicates that it must been made to the product.
When I work with a product manufactured in my lab (enrofloxacin at 10% w/v) and I prepare this product (per triplicate) at level of standard 1, 2 and 3, my CV is so high that the number of replicates obtained using the relation mentioned above, are more than five but when I work with another product manufactured in my lab with the same formula (enrofloxacin at 5% w/v) my CV is enough to do one replicate only.

[Narendra]

What is the formula ? Repetability with matrix or without matrix ?
Are U getting precision with single level standard ?

Narendra

[angupa]

Repetibility with matrix and with three level standards.

The formula is CV = I100-LAI*√n/Z where

LA= value limit accepted
n= nº replicates that must been done
Z(α = 0.01) = 2.58
For example, if the acceptance interaval is 95.0 - 105.0 the maxim CV in case of 1 replicate is 1.94, in case of 2 replicates is 2.74, in case of 3 replicates is 3.36

[Narendra]

As U said with matrix and three level standard. Are U getting precision with three level standard. First try to get precision within limit for standard level and than even you don't get acceptable result with matrix it means your extraction method for matrix or linearity of method not correct. In such case dilute the concentration.