At left, the Leco CNS 2000 simultaneous C, N, and S analyzer with solids autoloader.

Analysis of carbon, nitrogen, and sulfur is often an important characteristic of environmental samples, and given the difficulty of analysis, specialized instruments have been developed for their determination. For soils, rocks, and waste materials, dry combustion methods which directly volatilize gases from solid samples are the standard. For solutions, N can be measured as NO3 or NH4 and S as SO4 by methods described under ion analysis. Dissolved aqueous carbon (organic or inorganic) can be determined by the DOC analyzer described below. C, N, and S in Solids The Leco 2000 analyzer in the Lab simultaneously determines C, N, and S in solid samples within the approximate range of 0.05 to 5% by weight of each element (varying with sample size used). The sample is weighed into a tared ceramic boat and loaded into the autoloader where it combusts in a furnace at 1350 oC. Approximately 1 g of combustion catalyst is added to each sample to ensure complete combustion of the sample in the furnace. Combustion gases are collected in a 4.5-liter ballast tank and then flow to the detectors. C and S (as CO2 and SO2) are detected by infra-red absorption measurement, and N2 by thermal conductivity detection. The method is suitable for analysis of soils, sediments, sludges, and plant tissue. Sample masses of up to 4 g can be analyzed (recommended for soils where % CNS is relatively low) ensuring representative sample analysis. For plant tissue sample weights of about 200 mg are generally sufficient for CNS quantification, although at least 1 g of sample should be submitted to provide enough sample mass for duplicate analysis. To ensure homogeneity, it is recommended that samples be air-dried and finely ground. Sample prep. can be performed at the Contaminant Analysis Laboratory for a minimal charge. Analysis of a certified reference material is performed every 10 samples as a check on instrument accuracy. A number of certified reference materials are available, so that most sample matrices can be matched fairly well. Aqueous Dissolved Carbon Dissolved carbon concentrations are determined using a Shimadzu TOC-5050A Total Organic Carbon Analyzer. The TOC-5050A has a wide linear range of up to 400 ppm organic carbon and 5000 ppm inorganic carbon, with detection limits around 300 ppb. For Total Carbon (TC), aliquots of aqueous sample are automatically injected into a total carbon combustion tube (680oC), carbon is oxidized to CO2(g) which then flows in a carrier gas stream to a nondispersive infrared (NDIR) detector where the CO2 content is measured. The output is displayed as peaks and quantified by peak area using a calibration curve constructed from 4 calibration standards. For Inorganic Carbon (IC), aliquots of sample are injected into an IC reaction vessel (phosphoric acid solution) where CO32-and HCO3- are converted to CO2 which then flows directly to the NDIR detector. When both measurements are performed on a single sample, Dissolved Organic Carbon (DOC) is quantified as the difference between TC and IC concentrations as DOC = TC - IC. Samples for aqueous C measurements should be filtered at at least 1 micron (42 Whatman) to prevent clogging of the instrument; filtering may be done at the Lab for an additional fee (see price list for details.