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- Posts: 8
- Joined: Wed Nov 11, 2015 4:36 pm
When calibrating with solutions composed of strictly BAC and water, testing a sample of strictly BAC and water results in an extremely accurate reading by the instrument. Specifically, I was getting 0.1200% and 0.1201% results on an injection of a sample that I formulated to be 0.12%. I followed this up by shooting a sample of our soap (with other raw material components) that I formulated to be 0.12% BAC and the result was between 0.10% and 0.11%. From this I was confident that I could conclude this inaccuracy was due to the matrix of the soap rather than an inconsistency of the HPLC. I confirmed these findings by performing this procedure in triplicate which produced nearly identical results.
Due to this conclusion, I then developed a calibration method that would account for the matrix present in our soap. I made a 0.09%, a 0.12%, and a 0.15% BAC soap solution that included the other raw materials at their regular concentrations. I then injected each of these samples by weighing up 24-25g samples of each and diluting them into a 100mL volumetric with deionized water. I set the calibration level by multiplying the sample weight by the %BAC used in formulation. After calibrating, I made up a separate sample of our soap at 0.12% and ran it as a check standard. Across 15-20 injections, this sample ran in the range of 0.1175-0.1125%.
I concluded that for accurate results it is imperative to account for the interference of the raw materials in the calibration solutions. I then proceeded to perform a validation on this method by testing linearity, repeatability, ruggedness, and an outside verification of a sample. As far as I’m concerned, this method is ready to be implemented into our FDA regulated procedure.
I am wondering if anyone else in the industry does something like this testing scheme by calibrating specific to the matrix of a sample that they intend to test.
One of the other issues with this method is that our BAC has 3 homologues (C12, C14, and C16). One region of concern is that when in the soap matrix the C16 peak is relatively small and almost always requires manual integration. I have spent hours attempting to adjust the integration events to allow for auto-integration of the chromatograms without much success for application across multiple chromatograms. When shooting a sample that does not include the accessory raw materials of the soap, the chromatography is very clean and the C16 peak separates away from the baseline enough for consistent auto-integration with our current integration settings. Our QA personnel is very hesitant to allow us to continue to manual integrate due to possible further questioning from auditors.
Would it be possible to separate glycerin and Caltaine C-35 from the solution to allow for cleaner chromatography?
Caltaine C-35 is Cocamidopropyl Betaine
BAC is also known as BZK (specifically Benzalkonium Chloride)