Chapter 12
Sampling, sample preparation and dosing
Your project partner insists that the water samples are exchanged after SPE into DMSO. DMSO is a non-volatile solvent, and it should not exceed 0.1% in the final bioassay. You have 1 L of water. Into which volume of DMSO do you need to enrich your 1L of water that you can dose at a relative extraction factor REF of 100 in your bioassay?
Is that a practically feasible approach? What is a way out of the dilemma?
Plan the dosing for a reporter gene assay for estrogenicity with the samples from 12B2. In your dosing plate at the highest concentration, you want to have 200 µL of 4x the final relative extraction factor REF that you want to achieve on your cell plate, which is then serially (1:2) diluted 11 times covering a REF range of 1024. Please refer to figure 12.8 in Chapter 12 on a typical dosing scenario in a bioassay.
From experience you know that there is about 2-20 ng/L EEQ in a WWTP effluent, and the treatment efficiency of a WWTP is typical 80-90%. In surface water you get a 10- to 100-fold dilution of the effluent and in drinking water you should in theory have no residues left.
In the assay you use, the EC10 of estradiol is 1.1.10-11 M, the molecular weight MW(E2) =272.4 g/mol.
Can you use the methanolic extract as it is or do you recommend to blow down the solvent prior to preparing the solution in the dosing vial?