We viewed the chromatograms before performing the PSD cleaning and found severe contamination in the last extraction. The hexane blank that had been removed from the reagent bottle and placed on the GC was clean. However, the reagent blank that had been through the PSD method (dialysis, blow down, transfers, etc.) was very contaminated. A chromatographic comparison between the reagent blank and the lab spike (which also went through the method) is shown below (lab spike consists of 200 uL of a 1ppm dilution of Chemservice organochlorine pesticides mixture #1 – 508 in MTBE, cat # OCP508-1JM spiked into 100 mL hexanes, then extracted by the PSD method). Note that retention times, compound labels, and baselines have been removed for clarity.
A discussion with the CERES staff resulted in a careful evaluation of the entire extraction process. As this contamination occurred in the reagent blank, it could not be from the field extraction and therefore must have occurred during the dialysis, blow down, or transfer.
Today we are extracting a new reagent blank, a blank LFT, and the acetone from the wash bottle (used to clean the Rotavap-RBF joint between samples). Dirty glassware is suspected, however, several measures are being taken to rectify the situation. All glassware for the CERES/OSU split extraction is being cleaned again. The split extraction will not proceed until the situation is satisfactorily remedied.
In contrast, the standards appear much better. Below is an example.
1 comment:
EVERY lab at one time or another has had to deal with contamination issue. Yes, glassware is often the culprit. But it is also often warranted at these times to take a good look at the overall operation and see if there are other potential vunerable processes were contamination could entire the process.
GLASSWARE:
Most good chemists are very picky about the glassware, many do their own. A casual approach by a laboratory or chemists to glassware generally is cause for worry.
Glassware washing is not a "low rung" job or unimportant it is the BEGINNING and END of every analysis. You often get the same casual approach to water (as a reagent it is very very important) but because it is so common in life ("glassware does not egual kitchen dishes") there is a tendency to dismiss its value and the value of those that are responsible. Glassware is THE MOST IMPORTANT piece(s) of equipment in the laboratory, they require care and TLC, cleaning and MAINTANING clean glassware is key to data quality.
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