A method for the determination of 30 individual organochlorine pesticides, total toxaphene, and total poly chlorinated biphenyls (PCBs) in aquatic bottom sediment is described and laboratory performance data are provided. The method was developed in support of the U.S. Geological Survey's National Water-Quality Assessment program and is based on conventional Soxhlet extraction using dichloromethane. Two aliquots of the sample extract are quantitatively injected onto a styrene-divinylbenzene gel permeation column and eluted with dichloromethane. This gel permeation chromatography step removes inorganic sulfur and large naturally occurring molecules from the sediment extract. The first aliquot is analyzed for semivolatile organic compounds by gas chromatography with mass spectrometric detection. The second aliquot is further split into two fractions by combined alumina/silica adsorption chromatography prior to determination of the organochlorine pesticides and PCBs by dual capillary-column gas chromatography with electron-capture detection (GC/ECD). This report completely describes and is limited to the determination of the organochlorine pesticides and PCBs by GC/ECD. Current (February 1995) data-reporting limits have been set at 1 to 5 micrograms per kilogram for 30 chlorinated pesticides, 50 micrograms per kilogram for total PCBs, and 200 micrograms per kilogram for toxaphene. SAFETY CONSIDERATIONS This method involves the handling of known, suspected, and possibly unknown hazardous chemicals and reagents. The method uses substantial volumes of dichloromethane, a suspected carcinogen, during sample extraction and some extract clean-up steps. The USEPA has special regulations covering the handling and disposal of PCBs. Carefully follow all standard safety practices regarding the use of solvents, compressed gases, OC pesticides, PCBs, polycyclic aromatic hydrocarbons, and other method-related chemicals. Consult material safety data sheets for additional safety information. Always wear appropriate protective clothing, gloves, and eye wear, and use adequate ventilation when preparing samples or standard solutions. Electron-capture detectors (ECDs) contain radioactive 63nickel and must not be opened by unlicensed operators. ANALYTICAL METHOD Organic Compounds and Parameter Codes: Organochlorine pesticides and gross polychlorinated biphenyls, bottom sediment, gas chromatography, O-5129-95 (see table 1)
A method for determining submicrogram-per-liter concentrations of caffeine in surface water and groundwater samples has been developed. Caffeine is extracted from a 1 L water sample with a 0.5 g graphitized carbon-based solid-phase cartridge, eluted with methylene chloride-methanol (80 + 20, v/v), and analyzed by liquid chromatography with photodiode-array detection. The single-operator method detection limit for organic-free water samples was 0.02 μg/L. Mean recoveries and relative standard deviations were 93 ± 13% for organic- free water samples fortified at 0.04 μg/L and 84 ± 4% for laboratory reagent spikes fortified at 0.5 μg/L. Environmental concentrations of caffeine ranged from 0.003 to 1.44 μg/L in surface water samples and from 0.01 to 0.08 μg/L in groundwater samples.
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