handling background contamination when determining LOD and PQL

[IC-man]

I have a procedure where I dissolved a substance in a chlorinated solvent.  I then add water and extract the anions of interest.   The main one is Chloride.   For Chloride by instrument PQL detection is 0.01ppm.  I have calibrated .01 to 1.00ppm.   When I extract the blank 10 times the mean  is 0.13mg/L RSD .03mg/L.  Would it be logical to raise the reporting limit, maybe to 0.25mg/L.  Since I know the contamination will always be present.   When samples are analyzed in the future just subtract the Average of 3 blanks extracted with the samples.   When calibrating very low then many times the background blank will limit the detection limit?

Thanks, 

[The_Ion_Lady]

Hello @IC-man ,  apologies for the delay response but had some time out in the mountains 😊. 

I personally would not raise the limit because from experience the solvents used can change from batch to batch. Also, if the manufacturers changes their process then the level will change too, or if you have to change suppliers. The background should be judged on what you are using for that run sequence.

If you are using the same diluent and prep as your samples with the standards, your calibration curve will compensate what is in your diluent. Just remember to use the same diluent all the way through.

Good-luck!

[IC-man]

Thanks for the advice.  The mountains is relaxing!!  I tried the blank subtraction, and it is not worth it.   I will probably have to use polar organic solvent like DMAC and make a bigger dilution.      I like the phase separation because the baseline looks better(chlorinated solvent).   MECL2 is great for most polymers.  The chloride is very low.  The polymer that I am currently working with does not dissolve well in MECL2.  I have to use Tetrachloroethane(TCE).  TCE has more free chloride. 

By the way changing from the AS19 4um to a AS18 was the winner for separating Formate from Methane sulfonate.  Thanks.