The overall goal of this procedure is to demonstrate preparation, extraction, and analysis of pesticides using five different passive sampling devices and to show how to calibrate them in the laboratory for field application. Passive sampling is a promising tool to answer quick questions for measuring pesticides, continuously at low concentration levels to improve for example, environmental risk assessments. The main advantage of passive sampling is that it's a simple time-integrated method for measuring a broad range of pesticides in aqueous environment.
This method is a valuable tool for monitoring of pesticides in water. It can also be used for non-target analyzers, toxicity testing, and as an alternative for sediment and biomonitoring. Following this procedure, sampling rates and passive sampler water partitioning coefficients can be calculated based on the uptake profile for individual pesticides.
Cut silicone rubber sheets into stripes of 2.5 millimeters by 600 millimeters and 2.5 millimeters by 214 millimeters using a stainless steel cutter. Connect them using a stainless steel blind rivet with a rivet gun to obtain a total sampler stripe size of 2.5 millimeters by 914 millimeters. After cleaning the silicone rubbers by socket extraction as described in the text protocol attach a silicone rubber stripe to a stainless steel spider sampler holder by wrapping the silicone rubber stripe around the rods on the holder.
Attach each end of the silicone rubber stripe to a rod on the holder to the loop at the end of the silicone rubber stripe. For POCIS A place 220 milligrams of HLB bulk sorbent between 2 9.0 centimeters by 9.0 centimeters square PES membranes. For POCIS B, place 220 milligrams of a sorbent mixture between two PES membranes.
Compress the sorbent and the two PES membranes between two stainless steel rings manually, and secure onto a stainless steel sample holder. Next, place the SDBRPC and C18 disks between two PES membranes. Similarly compress the disks and two PES membranes between two stainless steel rings manually and secure onto a stainless steel sample holder.
Fill the three tanks with natural water. Perform all experiments at a constant water temperature and under turbulent water conditions using two electric pumps attached to the tank wall on each side. Also perform the experiments in the dark to minimize the effect of photo-degradation.
Next spike each glass container with a pesticide standard mixture containing 124 pesticides using a glass syringe. Conduct the uptake study in rectangular 95 liter glass containers. Designate tank one for silicone rubber, tank two for POCIS A, POCIS B.And tank three for SDB-RPS disk C18 disk.
Take out the passive samplers manually from the tanks at time intervals of 5, 11, 20, and 26 days to determine the sampling rates of the pesticides. In addition, monitor the concentrations of the pesticides in each tank by collecting 100 milliliter water samples at day 0, 5, 11, 20, and 26. Prior to extraction, dry the silicone rubber stripe under a stream of high purity nitrogen gas.
For gas chromotography mass spectrometry analysis, carry out the solid liquid extraction using sockslet extraction. After placing the silicone rubber into the sockslet extractor add 250 milliliters petroleum ether and acetone and 3 boiling stones into the round bottom flask. Spike the silicone rubber with 100 microliters of an internal standard mixture using a pipet.
Then add 50 milliliters of petroleum acetone into the sockslet extractor. Switch on the heater and run the sockslet extraction for 19 hours and then switch off the heater. Concentrate the extracts by rotory evaporation followed by gentle nitrogen blowdown to one milliliter.
Exchange the solvent to 90 to 10 cyclohexane to acetone by adding 3 times 1 milliliter of cyclohexane acetone during the nitrogen blowdown to 1 milliliter. For liquid chromotography tandem mass spectrometry analysis the silicone rubber is extracted with 300 milliliters of methanol. Exchange the solvent to a acetonitrile by adding one milliliter of acetonitrile during the nitrogen blowdown to one milliliter.
Open the POCIS sampler carefully and transfer the sorbent with ultra-pure water using a funnel into a pre-cleaned empty polypropylene solid face extraction cartridge containing two polyethylene frets. Dry the sorbent by vacuum to remove water. Prior to elution, spike the sorbent with 100 microliters of an internal standard mixture using a pipet.
Elude the POCIS A and POCIS B cartridges using 1.5 milliliters of methanol followed by 8 milliliters of 80 to 20 dychloromethane to methanol for LCMSMS analysis. Concentrate the extracts to 1 milliliter by gentle nitrogen blowdown before exchanging the solvent to acetonitrile by adding 1 milliliter of acetonitrile during the nitrogen blowdown to 1 milliliter. For gas chromotography mass spectrometry analysis POCIS A and B is eluded using 5 milliliters of ethyl acetate and the solvent is exchanged to 90 to 10 cyclohexane to acetone by adding 3 times 1 milliliter of cyclohexane to acetone during the nitrogen blowdown to 1 milliliter.
Transfer individual disks of SDB-RPS and C18 into a glass beaker and dry them under nitrogen gas. Spike the disks with 100 microliters of an internal standard mixture using a pipet. Sonicate the disks two times in a glass beaker at room temperature.
First with five milliliters of ethyl acetate for ten minutes and then with three milliliters of ethyl acetate for ten minutes. Transfer both extracts into one glass tube before concentrating them to two milliliters by gentle nitrogen blowdown. Split the samples into two one millimeter fractions for GCMS and LCMSMS analysis.
In one fraction concentrate the extracts to 0.5 milliliters by gentle nitrogen blowdown and then exchange the solvent to cyclohexane and acetone for GCMS analysis. For LCMSMS analysis concentrate the extracts to 0.5 milliliters by gentle nitrogen blowdown and exchange the solvent to acetonitrile. Shown here are exemplary results for the uptake of acetamiprid in silicone rubber in nanograms showing a linear uptake from day 0 to 20 and then a curvilinear uptake from day 20 to 26.
This plot shows exemplary results for the uptake of dimethoate in silicone rubber in nanograms. Showing a linear uptake from day 0 to 10 and then an equilibrium after day 10. The five tested passive samplers were capable of accumulating pesticides with a wide range of different octenol water partition coefficients showing that silicone rubber is more suitable for hydrophobic compounds, whereas more polar compounds were better taken up by POCIS A, POCIS B, and SDB-RPS disk.
After watching this video you should have a good understanding how to prepare, extract, and analysis pesticides using five different passive sampling devices and how to calibrate them in the laboratory. While attempting this procedure it's important to remember that this study was performed under static conditions while future uptake study should consider using follow-through exposure or in calibration. The usage of performance compounds, which are spiked to the passive sampler before deployment can be used to calculate n-zeto sampling rates and allow for more accurate estimates of time-rate average concentration.
Please don't forget, working with organic solvents acets and basics can be extremely hazardous and precautions like lab coat, gloves, eye protection, should be taken while performing this procedure.
