[dPaabo]

Hey there, first post  I graduated a few years ago and have been doing environmental science in varying capacities since. I recently started working wet chem, and have been tasked with analyzing the PT for ASTM Method 3230, Salt in Crude Oil. It's basically a Conductivity or Salinity test, probe and all.. but it requires dilution first with an organic solvent, then with an alcohol mixture. The analyst who analyzed the last PT failed- he was much too high (by about ~9x the established value). We still had some of this sample left over, and I decided to analyze that as well, for QC. I first established a 7-point curve (R=0.9997) from 1-151 ptb, and prepared my QC and samples, transferring them to clean jars and letting them come to ~20°C (the probe auto-corrects and displays Con @ 25°C as well as current temp anyways, but samples need to be analyzed within 3°C of the curve).

I carefully wash and dry everything between readings; first the probe, then the beaker, and I always let everything dry completely before continuing (I had a problem earlier on in the process with hexane contamination because I was being too impatient ). I make sure the sample is well-homogenized as well. I take every precaution I know.. Then I read the results of the QC.. roughly 10x the reported value.

I am hesitant to report on the current PT while I am so unsure of why I can't get a reasonable reading of the old one. While the results I'm getting ARE much more reasonable for the current PT, my results seem to be inconsistent. (My first two samples were within 10% of each other, but the one I ran today was ~30% lower, still..) I'm thinking the old PT was poorly-extracted, or poorly stored. I'm going to reach even further back on monday and see if I can find the yet older PT sample and try that, as well as running my current PT a few more times to try and get more consistent results.

Anyone else ever done this method? Am I missing a step where I'm supposed to make a 1:10 dilution of the sample? Because that would magically fix my problems. Any helpful words or advice?