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Exactly how much difference does a cosolvent make and what is a cosolvent anyway?

Last week a customer noticed that instead of using only Carbon Disulfide when desorbing our Organic Vapor Monitors (566, 546, and 525), we also use a cosolvent.

A cosolvent is an additional solvent added to a desorption solution to increase the recovery of the chemical of interest.  For example, if you desorbed the 566 badges for Acetone in just 2 mL of Carbon Disulfide, the recovery will be about 76%.  But if you add three percent Benzyl Alcohol the Acetone recovery changes to 94%.

The table below shows how the recoveries changed for a variety of different organic chemicals

Mixture A                  100%                          Carbon Disulfide

Mixture B                  97%/3%  Carbon Disulfide / Benzyl Alcohol.


2 mL Ethyl alcohol Acetonitrile Acetone PGMEA 2-Ethylhexyl Acrylate Benzene o-Xylene Methylene Chloride Hexane
Mixture A 47.8 67.4 76.2 72.7 95.3 95.0 93.4 98.8 97.6
Mix B 86.2 87 93.8 98.9 102 97.5 97.3 96.3 98.8
Percent Increase / Decrease +38.4 +19.6 +17.6 +26.2 +6.7 +2.7 +4.0 -2.5 -1.2

As you can see, there can be a significant difference when using cosolvents.  In this case, the recoveries of the polar chemicals were greatly improved.  While the recoveries of the non-polar chemicals already recovered in the high 90s, were not significantly changed.

There is another way to raise your recoveries without changing solvent mixtures. with solvents.  Do you know what it is?  Check out the next blog… and think about media to solvent ratios.  You really have more control than you think.