Chemiluminescence detector redox

More recently, chemiluminescence detectors based on redox reactions have made possible the detection of many classes of compounds not detected by flame ionization. In the redox chemiluminescence detector (RCD), the effluent from the column is mixed with nitrogen dioxide and passed across a catalyst containing elemental gold at 200-400°C. Responsive compounds reduce the nitrogen dioxide to nitric oxide. The nitric oxide is reacted with ozone to give the chemiluminescent emission. The RCD yields a response from compounds capable of undergoing dehydrogenation or oxidation and produces sensitive emissions from alcohols, aldehydes, ketones, acids, amines, olifins, aromatic compounds, sulfides, and thiols. 

S. Nyarady, R. Barkley, et al., Redox chemiluminescence detector application to gas chromatography, Anal. Chem., 37 2074-2079... 

S. Montzka and R. Sievers, Redox chemiluminescence detectors for chromatography, Chromatography, 2 22-26 (1987). 

The redox chemiluminescence detector (RCD) is also based on the nitric oxide-ozone reaction. However, unlike the two detectors previously described, the analytes do not contain any oxidizable nitrogen. In this case a nitrogen-containing reagent such as nitrogen dioxide or nitric acid is reduced to nitric oxide by the analyte at a heated gold surface (reaction [IV]) ... 

TEA, thermal energy analyzer NSD, nitrogen selective detector RCD, redox chemiluminescence detector. 

This reaction mechanism was first proposed by Halsted and Thrush (30) when studying the kinetics of elementary reactions involving the oxides of sulfur. Visible and UV spectroscopic studies (31) confirmed that the chemiluminescent emission was from SO2. Recently, it has also been confirmed that the sulfur- analyte molecule from the GC effluent is converted to SO in the flame of the SCD (32). Even though SO is a free radical, it can be sufficiently stabilized in a flow system under reduced pressure (33,34) to be sampled and transferred to a vessel to react with introduced O. Based on these operational principles. Burner and Stedman (33) concluded that SO produced in a flame could be easily detected. They modified a redox chemiluminescence detector (36) to produce what was termed a Universal Sulfur Detector (USD). A linear response between 0.4 ppb and l.S ppm (roughly equal to 3 to 13,000 pg of S/sec) was demonstrated with equal response to the five sulfur compounds tested. This detection scheme has been utilized as the basis for the commercially available GC detector. 

PTV programmed-temperalure vaporization r column radius RCD redox chemiluminescence detector peak resolution... 

Similarly, the sulfur chemiluminescence detectors (SCD), namely fluorine-induced SCD (FSCD), ozone-induced SCD (O-SCD) and redox CD (RCD), work by first oxidising the organosulfur compound to give a species which may either react with fluorine or ozone to form a chemiluminescence species (HF and SOj, respectively). Reaction equations for O-SCD at 800-1100°C, developed by ref. [555], are ... 

Detectors commonly used in GC and specified in the USPP include FID, alkali FID (NPD, TD), BCD, and TCD. A description of these detectors, including their operational principles and relative performance, was presented in a previous volume of this encyclopedia. Various other useful detectors for GC include photoionization (PID), flame photometric (FPD), electrolytic conductivity (BLCD), redox (RCD) and sulfur chemiluminescence (SCD), and helium ionization (HID).[4 1 Table 1 summarizes some of the features of detectors used in GC. 

The chemiluminescence-redox detector (CRD) is based on specific redox reactions coupled with chemiluminescence measurement. An attractive feature of this detector is that it responds to compounds such as ammonia, hydrogen sulfide, carbon disulfide, and sulfur dioxide. Hydrogen peroxide, hydrogen, carbon monoxide, sulfides, and thiols that are not sensitively detected by flame ionization detection can be detected with the CRD detector. Compounds that typically constitute a large portion of the matrix of many industrial samples are not detected, thus simplifying matrix effects and sample cleanup procedures for some applications. 

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