Chromatography Forum

Hello,
I'm looking for some advice.
I am trying to optimize a method to extract olamine piroctone from solid soap.
I'm basing it on a method that requires extraction in methanol and dichloromethane (+ ultrasonic bath), then in a volumetric flask, the methanol/acetic acid mixture is filled to the mark.
The soap is averaged on a cryogenic mill before analysis.

I get very reproducible results. where RSD% = 1-2%, even between a series of 12 replicates, and Recovery of 90-100% (spike sample)

The problem is that the declared content is about 1% [g/100g], another lab gets a result of about (for example) 0.97, I get 0.86.

It uses a certified reference material, the calibration curve is stable. The peaks are reproducible. HPLC-UV/DAD method.

Is it possible that I am losing some % of analyte somewhere? If so, where? I have heard that analyte can form complexes with iron if it has been in direct contact somewhere.

I've extracted many analytes from solid soap. If me: I'd find out if olamine piroctone is soluble in N,N-dimethylformamide or pyridine.

In the old days, we used a blender and solvents then assayed the filtered liquid by GC or HPLC, faster than what you are trying. Later on, we used a high speed homogenizer to speed up the process and to use less solvent volumes.

So I'd personally see in which solvents my analyte is soluble in. Otherwise, I'd have to "guess" that particle size, or your ultrasonic mixing step, is responsible for the variable results.