Sulfur-selective chemiluminescence detector

Because process mixtures are complex, specialized detectors may substitute for separation efficiency. One specialized detector is the array amperometric detector, which allows selective detection of electrochemically active compounds.23 Electrochemical array detectors are discussed in greater detail in Chapter 5. Many pharmaceutical compounds are chiral, so a detector capable of determining optical purity would be extremely useful in monitoring synthetic reactions. A double-beam circular dichroism detector using a laser as the source was used for the selective detection of chiral cobalt compounds.24 The double-beam, single-source construction reduces the limitations of flicker noise. Chemiluminescence of an ozonized mixture was used as the principle for a sulfur-selective detector used to analyze pesticides, proteins, and blood thiols from rat plasma.25 Chemiluminescence using bis (2,4, 6-trichlorophenyl) oxalate was used for the selective detection of catalytically reduced nitrated polycyclic aromatic hydrocarbons from diesel exhaust.26... 

Ryerson, T. B., Dunham, A. J., Barkley, R. M., and Sievers, R. E., Sulfur-selective detector for liquid chromatography based on sulfur monoxide-ozone chemiluminescence, Anal. Chem., 66, 2841, 1994. 

An alternative to FPD in the sulfur mode is the sulfur chemiluminescence detector (SCD) (48). This detector works by forming sulfur monoxide in a reducing flame. Sulfur monoxide is detected by its chemiluminescent reaction with ozone. The SCD is at least one order of magnitude more sensitive than most FPDs. It provides a linear response with high selectivity and does not suffer considerably from quenching. 

S.E. Eckert-Tilotta, S.B. Hawthorne and D.J. Miller, Comparison of commercially available atomic emission and chemiluminescence detectors for sulfur-selective gas chromatographic detection, J. Chromatogr., 591, 313-323 (1992). 

Any sulfur-selective detector may be used e.g., electrolytic conductivity, flame photometric, or sulfur chemiluminescence. The detector must be capable of detecting less than 0.1 ppm v/v of carbonyl sulfide with a signal-to-noise ratio of 10 1. 

Gas chromatography with either sulfur chemiluminescence detection or atomic emission detection has been used for sulfur-selective detection. Selective sulfur and nitrogen gas chromatographic detectors, exemplified by the flame photometric detector (FPD) and the nitrogen-phosphorus detector (NPD), have been available for many years. However, these detectors have limited selectivity for the element over carbon, exhibit nonuniform response, and have other problems that limit their usefulness. 

Practical aspects. Chemiluminescence detectors are only applicable as GC detectors because of signal quenching by high hydrocarbon levels such as solvents used as mobile phases in LC. They are primarily used for selective sulfur detection. 

Other even more sjjccific detectors can also be coupled to GCxGC. Atomic emission detectors (AEDs), and more element-selective detectors, such as sulfur compound detectors (sulfur chemiluminescence detector, or SCD), have been reported in the oil characterization area [84,85]. In these detectors, the combustion of sulfur compounds by an energetic induced plasma produces sulfur oxides that further react to and produce light at a specific wavelength that... 

Boduszynski and co-workers [114] and Andersson and Sielex [115] have used GC-AED to examine the sulfur-containing molecules in petroleum and its heavier processed products. Both groups found a preponderance of thiophenic sulfur compounds in processed materials, in contrast to petroleum. The unprocessed petroleum had mercaptans, sulfides, thiophenes, as well as other species containing other heteroatoms in addition to the sulfur. These two studies also showed that this detector has the selectivity for sulfur that is attainable with the two older commonly used sulfur detectors, the flame photometric detector (EPD) and the chemiluminescent detectors. The first of these, however, suffers from a very non-linear response. This effect is very compound-class dependent. This is due to the fact that the light-emitting species that is detected is a two-sulfur atom one that results from recombination of the sulfur atoms in the combusted sample peak. The efficiency of combustion and the rate of recombination are both dependent on the... 

Element selective detectors Element selective detectors applicable in pesticide residue analysis include electron capture detector (ECD), electrolytic conductivity detector (ELCD), halogen-specific detector (XSD), nitrogen phosphorus detector (NPD), flame photometric detector (FPD), pulsed flame photometric detector (PEPD), sulfur chemiluminescence detector (SCD), and atomic emission detector (AED). To cover a wider range of pesticide residues, a halogen-selective detector (ECD, ELCD, XSD) in conjvmction with a phosphorus- (NPD, FPD), nitrogen- (NPD), and/or sulfur-selective detector (FPD, SCD) is commonly used. A practical approach is to spht the column flow to two detectors that reduces the number of injections however, the reduced amoimt of analyte that reaches the detector must be considered. 

Obviously, the chromatographic principles are the same in process and laboratory GCs and they are built up in a very similar way. Standard detectors are in each case the thermal conductivity detector (TCD), which is a universal detector for all components, and the flame ionization detector (HD), which is a specific detector for hydrocarbons. To detect sulfur gases selective detectors like an electrochemical detector, chemiluminescence detector and, most important, flame photometric detector (FPD) are used. Gaseous fuels hke natural gas, synthetic gases, and blends are complex mixtures that cannot completely be separated in a single column. Two or more different columns must be combined. To monitor the fuel quality a quasi-continuous analysis is necessary this means that very short cycle times must be realized. To do so, high-boiling components are removed... 

A typical chemiluminescence detector consists of a series-coupled thermal decomposition and ozone reaction chambers. The selective detection of nitrosamines is based on their facile low-temperature (275-300°C) catalytic pyrolysis to release nitric oxide. Thermal decomposition in the presence of oxygen at about 1000°C affords a mechanism for conversion of nitrogen-containing compounds to nitric oxide (catalytic oxidation at lower temperatures is also possible). Decomposition in a hydrogen-diffusion flame or thermal oxidation in a ceramic furnace is used to produce sulfur monoxide from sulfur-containing compounds. 

The sulfur chemiluminescence detector (SCD) is heteroatom selective (for organic compounds with S atoms only) destructive mass-flow detector more sensitive and greater dynamic range than sulfur-phosphorous flame photometric detector (SP-FPD). 

There are a number of other GC detectors commercially available. Photoionization detectors (PIDs) are primarily used for the selective, low-level detection of the compounds which have double or triple bonds or an aromatic moiety in their structures. Electrolytic conductivity detectors (ELCDs) are used for the selective detection of chlorine-, nitrogen-, or sulfur-containing compounds at low levels. Chemiluminescence detectors are usually employed for the detection of sulfur compounds. The atomic emission detectors (AEDs) can be set up to respond only to selected atoms, or group of atoms, and they are very useful for element-specific detection and element-speciation work. 

Selective GC detectors aid in the detection and identification of compounds containing specific elements halogens with electron capture detector (BCD) or electrolytic conductivity detector (ELCD) nitrogen and phosjAorus with nitrogen-phosphorus detector (NPD) sulfur and phosphorus with flame photometric detector (FPD) and sulfur with sulfur chemiluminescence detector (SCD). The development of the atomic... 

Sulfur Chemiluminescence Detector. Another sulfur selective detector based on photometric sensing of a chemiluminescent reaction has become commercially available (Sievers Research, Inc., Boulder, CO). Similar to the FPD, the detection scheme of the SCD incorporates combustion of the GC column effluent in a hydrogen rich flame. However, the sulfur species detected is an excited state of sulfur dioxide (SO2 ), not... 

Instrumentation and Methods. A Sievers Sulfur Chemiluminescence Detector Model 350 was utilized for the selective detection of sulfur compounds. The electronics were set to integrate photon counts for 0.12 seconds. Supply air to the ozone generator was set at 8 psi., and the reaction vessel pressure was measured at 12-14 torr. 

The chemiluminescent detector is a mass-sensitive detector, which is highly selective for either sulfur (SCD) or nitrogen (NCD), depending on the instrumentation. The mechanism of detection is a two-step process with initial combustion followed by low-pressure reaction with ozone. The oxidation products emit a characteristic light, which is measured. The detection limit is about 0.5pgSs and 3 pg N s and the linearity is 10". One main use is the determination of sulfur compounds in petrochemical products. 

Sulfur Chemiluminescence Detection—As sulfur compounds elute fiom the gas chromatographic column they are combusted in a flame ionization detector (FID). These combustion products are collected and transfer to a Ifur chemiluminescence detector (SCD). This detection technique provides a highly senative, selective, and linear response to volatile sulfur compounds and may be used simultaneously while the usual fixed gas and hydrocarbon determinations are being made. 

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