Carbon (Total, Inorganic, Organic)
Carbon values are determined either through combustion analysis and/or coulometric titration. For total carbon, an elemental analyzer is used which burns the sample in pure oxygen, producing combustion products which are then analyzed using a thermal conductivity detector, or measured as they pass through infrared cells. For inorganic carbon, carbon dioxide is liberated when the sample is heated and acidified, which is then swept into an absorption cell and is titrated coulometrically. Organic carbon may be calculated by subtracting the difference between the total and inorganic carbon values. Alternatively, for aqueous sample materials with low levels of carbon, total organic carbon can be determined using a TOC Analyzer, which combusts the sample and measures the combustion products using non-dispersive infra-red (NDIR) detection.
Hydrogen values are determined using an elemental analyzer for combustion analysis. The instrument burns the sample in pure oxygen, producing combustion products of carbon dioxide, water, and nitrogen which are then separated and analyzed in a thermal conductivity detector, or measured as they pass through infrared cells. The results are calculated from a response factor, and based on sample weights.
Nitrogen (Combustion, Kjeldahl)
Nitrogen is determined by the use of either an elemental analyzer for combustion analysis, or using the Kjeldahl technique. For the combustion technique the instrument burns the sample in pure oxygen, producing combustion products of carbon dioxide, water, and nitrogen which are then separated and analyzed in a thermal conductivity detector. The results are calculated from a response factor, and based on sample weights. For the Kjeldahl technique, the sample is digested with sulfuric acid, sodium sulfate, and copper sulfate. The organic material is oxidized and the nitrogen converted to ammonium sulfate. The resulting ammonia is distilled, absorbed in boric acid solution, pH adjusted, and titrated using sulfuric acid or analyzed using an ion selective electrode.
Oxygen is measured using a combustion technique where the instrument pyrolyzes the sample in an inert atmosphere (helium). During the pyrolysis, nitrogen, hydrogen, and carbon monoxide are formed when they contact a nickel-plated carbon catalyst at 1060°C. These products separated via a chromatographic column, and the carbon monoxide is analyzed in a thermal conductivity analyzer, providing the oxygen percentage.
Sulfur values are determined using an elemental analyzer by combusting the sample at 1350 + 50°C in an atmosphere of pure oxygen. The sulfur is oxidized to sulfur dioxide, then quantitated by non-dispersive infrared absorption. Sulfur may also be tested using ICP-AES in most matrices.
For chlorine analysis, the sample is first combusted using either a Parr bomb or an oxygen flask to decompose the material and prepare it for instrumental analysis. The bomb technique is used to prepare samples for trace chlorine analysis by Ion Chromatography. For percent level chlorine, the sample is decomposed in an oxygen flask where the chlorine is converted to chloride and titrated potentiometrically with silver nitrate.
For the analysis of bromine, the sample is first combusted using either a Parr bomb or an oxygen flask to decompose the material and prepare it for instrumental analysis. The bomb technique is used to prepare samples for trace bromine analysis by Ion Chromatography. For percent level bromine, the sample is decomposed in an oxygen flask where the bromine in the sample is oxidized to bromate, and titrated with thiosulfate.
Fluorine analysis is performed using either oxygen flask combustion or pyrohydrolysis. With combustion the fluorine is converted to fluoride using a known volume of ionic strength adjustment buffer as an absorbing medium. From the resulting solution, an ion-selective electrode (ISE) determines the fluoride content. With pyrohydrolysis, the fluorine is separated from the sample by volatilizing it as hydrofluoric acid. This is accomplished with very high heat and moisture, then the liberated fluorine is measured with an ISE.
For the analysis of percent level iodine, the sample is first combusted in an oxygen flask where iodine in the sample is oxidized to iodate. The solution is treated with potassium iodide, liberating free iodine, and then titrated with thiosulfate. Trace measurements of iodine are performed by combusting the samples in an oxygen flask, then the resulting solution is analyzed by ion selective electrode.
For percent level halogens analysis, the halogens are converted to halides by oxygen flask combustion, and chloride, bromide, and iodide are determined potentiometrically with silver nitrate. The result is reported as Total Halogens as Chlorine. Analysis for trace halogens (chlorine, bromine, and iodine) is conducted on a Total Organic Halogen Analyzer. This instrument heats the sample in a quartz combustion tube during which the halogens are converted to halides and oxyhalides, transported to an absorber solution within a coulometric cell, and titrated against silver to the potentiometric endpoint. These techniques give aggregate results for total halogens or total halides, and do not provide individual results for each element.
Metals services provide an extensive range of preparation techniques and instrumentation methods that can be utilized to measure Group I metals, Group II metals, Transition metals, Metalloids (i.e. boron, silicon, germanium, etc.), and some Non-Metal elements (i.e. sulfur and iodine) in a wide variety of sample matrices. Preparation methods include wet ash digestion, water dilution, solvent dissolution, dry ash, microwave assisted acid digestion, and several types of fusions. The types of instrumentation available are ICP-AES, ICP-MS, FAA, GFAA, and CVAA. Click here for additional information.