Detection of Common Chlorinated Pesticides in Water by Gas Chromatography E. F. Neuzil and D. J. Stone Western Washington University, Bellingham, WA 98225
In order to introduce the basic techniques ofgaschromatography to students during their initial year in the chemis& laboratom. ". we have develo~eda fairlv .r a.~ i ddetermination of pesticides using these techniques. It is based on the work ofdunk and Rlchards (11whose ~rweduresdo not require internal standards. This provides an easy experiment with high student interest performed near the end of the full-year sequence laboratory as an example of micro analysis used in a qualitative and, within limits, quantitative determination. Confirming the results of Junk (1) most students recovered m a t e r than 80% of each pesticide. This is illustrated in.the table. Values obtained-were somewhat low but usually within 20 ppb ofthe correet values. If the student did not follow pr&isely the protocol we developed, no results were obtained or revealed contaminated samples. In order to allow as many students as possible to inject their final water analysis sample, a copy of a recently obtained gas chromatogram of a set of nine pesticides was given to each student pair that also listed the order of exit, retention times, and the parts per billion that each peak represents. This was then used to identify and quantify each pesticide in their unknown, which was 100 mL of tap water laced with four of the pesticides to a concentration of about 50 ppb. Each student was issued a set of solvents with Teflon seals containing ethyl acetate, anhydrous methanol, and ultra pure water. The solid phase extraction pack was a short body C-18 pack consisting of 100 mg of 37-55 m silica. The extraction pack was conditioned by ethyl acetate, methanol, and ultra water, in that order. The water sample (100 mL) was forced through the pack at 25 mumin with a glass syringe. The pack was then dried completely using aspiration. Two drops of ethyl acetate eluant were col-
lected under gravity flow in a 0.5 mL conical vial, 3 gL of which was injected into the gas chromatograph (HewlettPackard 5890 A Gas Chromatograph).The parameters are oven injection temperature at 200 'C flame ionization detector temperature 260 'C 30 m J & W Durabond-5 0.25 mM I.D. and -0.25 urn film column at 60 'C for 2 min and ramped 10 Running time was about 30 min. Literature Cited 1.Junk G. n: Richard, J. J. Aml. C h m . 1988.60.454.
Comparison of Actual Parts per Billion of Nine Pesticides to Typical Student Values Retention Time
Pesticide
Actual (ppb)
Student (ppb) 26 62
(min)
Lindane Heptachlor
10.18
27
19.04
56
Aldrin DDE
20.60 22.79 22.97
22 53 89
23.57 23.94
45 70
32 84 36 72
25.13 27.30
36 48
32 46
Dieldrin Endrin TDE DDT Methowchlor
28
Volume 70 Number 2 February 1993
167
