Chemical reaction detector , liquid chromatography

The form of the dissolved sulfur has not been characterized properly yet. While stable at ambient temperatures, a substantial amount can be converted to crystalline sulfur at elevated temperatures or by solvent separation. This observation led to the development of a rapid liquid chromatography method to determine elemental sulfur in SA binders. The procedure which has been described previously by Cassidy (17) is based on gel permeation principle and uses a Styragel column and a uv detector. Results showed that 2-14% of the elemental sulfur added reacted chemically with the asphalt. Petrossi (18) and Lee (19), who determined free sulfur by extraction with sodium sulfite followed by titration with iodine, calculated a higher percent of bonded sulfur in sulfur-asphalt compositions. The observed differences are most likely caused by variations in the asphalt composition with regard to polar aromatics and naphthene components as well as by reaction temperature and contact time. 

Chemical Analysis. Gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) techniques were used to analyze 4-chlorophenol and its oxidation intermediates. For GC-MS analysis, the samples were acetylated in pyridine. The samples were first evaporated to dryness. Then 200 xL of pyridine and 200 (xL of acetic anhydride were added to the dry residue. The samples were heated at 65 °C for 2-3 h to ensure the complete acetylation reaction, and then gently evaporated to dryness in a nitrogen stream. Finally, the residue was redissolved in 0.1 mL of hexane for GC analysis. A GC (HP model 5890) equipped with mass selective detector (HP model 5971) and SPB-5 capillary column (Supelco Co., PA., 25- X 0.2-mm i.d. X 0.33-p.m film thickness) was used. To separate different intermediate products, various oven-temperature programs were performed. The GC-MS interface line was maintained at 300 °C. The mass-... 

Selective detectors are much more useful for the selective quantitation of a small number of chemicals known to be present in a complex matrix than they are for identification purposes. The use of on-line chemical reactions can be very selective for certain chemical families (e.g.. amino acids, sugars). This technique has become widespread in column chromatography, both gas and liquid, and is even the principle underlying many detection schemes in thin layer chromatography [64]. The identification of an unknown presupposes methods supplying far more information and consistent with the ready association of elements of this information with structural details of the corresponding compound. 

The purity of SF was determined by gas-liquid chromatography as described by Hagler and Behlow (1981) using a Varian 3700 gas chromatograph with dual flame ionization detectors (Varian Instrument Co., Sunnyvale, CA). Slaframine samples and a SF standard regenerated from the dipicrate salt were derivatized in 2 ml vials with open-top cap and Teflon-silicon septa. One ml of each sample or standard was pipetted into a vial and the CH2CI2 evaporated under a stream of IM2. Each sample was derivatized with 100 yl TriSil BT (Pierce Chemical Co., Rockford, IL) for 30 min at room temperature. The reaction mixture was diluted with 900 yl CH2CI2. 

The term micro total chemical analysis systems (fi-TASs) is used now nearly exclusively for systems with a basic structure described in Chap. 9, Fig. 9.8. A liquid column moves through the device. It is driven either by a micropump or by electroosmosis. This moving column, also called the carrier stream, accepts a small sample volume increment, which is injected at the appropriate position. In the adjacent line, either a separation takes place (this is characteristic for chromatography and electrophoresis) or the sample reacts with ingredients of the carrier stream, thus forming a product which can be indicated. In both cases, at the end of the separation or reaction line, a detector is located which yields a concentration-dependent (better concentration-proportional) signal. 

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