Performance of an increased sensitivity method utilizing an extraction and concentration step to increase analyte concentration of the assayed sample is presented. Recently, Shepard and Carr (1992) reported a method for increased detection of atrazine by gas chromatography using C18 solid-phase extraction (SPE) with a 10 mL water sample. An application with BakerbondÒ C18 SPE columns for extracting and concentrating atrazine from 10 mL water samples is evaluated in this report.
MATERIALS AND METHODS
Equipment and reagents: C18 Bakerbond SPE columns (6 mL, 500 mg), vacuum manifold (12 position), vacuum pump, nitrogen gas, evaporating apparatus, 10-mL serological glass pipets, 10- by 13-mm glass test tubes. Analytical grade (pesticide free) ethyl acetate and methanol, atrazine (99.9% purity), Atrazine Rapid Assay, kit, Atrazine Sample Diluent, RPA-I Photometric Analyzer, Magnetic Separator Rack.
C18 Extraction and concentration of atrazine: Refer to application procedure on 'Detection of PPT Level of Atrazine in Drinking Water' (PPT Atrazine).
INTERPRETATION OF RESULTS
Using the RPA-I Photometric Analyzer, results of the Atrazine RaPID Assay are reported as ppb (ug/L) of atrazine. For the assayed samples, results are multiplied by 0.1 to calculate atrazine concentration of the original water sample.
RESULTS AND DISCUSSION
Precision: Samples of deionized water fortified with 95 ppt atrazine were extracted and concentrated by C18 SPE and assayed to determine precision in the method. The experiment consisted of three samples concentrated on three C18 SPE columns and each concentrate was assayed 4 times in singlicate in one run of the Atrazine RaPID Assay. The experiment was repeated four times. Variation between and within experiment runs and C18 SPE columns were estimated by the method of Bookbinder and Panosian (1986) using SAS software (1988). Within and between coefficients of variation for columns and experiment runs were below 10% (Table 1).
Analysis of deionized water: A study was performed to ensure that deionized water used in conditioning and rinsing C18 SPE columns was 'free' of atrazine. Water was deionized by a NANO pure ultrapure water system (Barnstead /Thermolyne, Dubuque, IA, USA). Water volumes of 15 to 105 mL were applied to Bakerbond (Malinckrodt-Baker) and Bond Elut LCR* (Varian) C18 SPE columns and concentrated, using the PPT Atrazine procedure, to a 1 mL volume in sample diluent for Atrazine RaPID Assay analysis (Table 2). A 15 mL sample volume represents the amount of water used in the conditioning and rinsing steps of the procedure. Increasing the volume of water to 105 mL (7 X 15 mL) and finding no atrazine indicates that this deionized water had no detectable level of pesticide that would interfere in the analysis of drinking water.