Chromatography Forum

I use PTFE, nylon absorbs thymol.

We get a concentrate that contains the active and some surfactants and probably water. From the concentrate, we dilute with DI and that is our finished product. This final dilution is what i'm testing that has 0.23% thymol in it.

I tried nylon, RC and PTFE filters, vs non filtered just now and the best filter was PTFE compared to the non filtered sample.

Do you filter your standard? If not, the 3-5% low recovery of your sample could be due to losses on the filter. How do you prepare your standard, dissolve pure component in MeOH? Is there any water or surfactant in your standard? If the standard and sample matrices are different filter losses will likely be different.

I filter everything. STD is 99.6% pure and dissolved in MeOH (or whatever diluent I am trying).
I will try recovery with an unfiltered sample today...

approximately how much water is in a recovery sample?

Spiked recovery sample is roughly 97% water, 2 g of this is diluted in diluent.

As you are catching flees (95% is not good for you, you need 98%). I guess this 3 % are important for manufacturer. Sometimes it is difficult to control this b***** black box (HPLC system).
If nothing works, try method of standard additions - this is foolproof, it does compensate for any hidden problems beyond our control (or lack of time to troubleshoot).

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"If your experiment needs statistics, you ought to have done a better experiment." Rutherford