Detectors thermal energy analyzer

Special identification detectors Thermal conductivity detector Thermal energy analyzer Temperature-programmed reduction Thermoparticulaie analysis Thermal volatilization analysis Thin-layer chromatography Titrimetry Volume changes... 

Detector Thermal energy analyzer. Thermo Electron Corp. Model 502A, furnace temp 575°, argon 15 mL/min, oxygen 25 mL/min, MeOH/dry ice slush bath... 

Chemiluminescent Detectors (Thermal Energy Analyzers) in Nitrosamine Analysis... 

VL medium, pH 6 4, with or without cells was incubated in sealed tubes for 10 hrs at 37 C NDMA was determined by gas chromatography with the Thermal Energy Analyzer as a detector (Thermo Electron Corp, Waltham, MA). The identity of NDMA was confirmed by 6C mass spectrometry. 

The data in Table I are also significant in terms of the type of analysis to determine the presence of NDMA. In all cases analysis was done using gas chromatography coupled with a Thermal Energy Analyzer, a sensitive, relatively specific nitrosamine detector (12). Further, in six of the studies, the presence of NDMA in several samples was confirmed by gas chromatography-mass spectrometry (GC-MS). The mass spectral data firmly established the presence of NDMA in the beer samples. 

Reliable analytical methods are available for determination of many volatile nitrosamines at concentrations of 0.1 to 10 ppb in a variety of environmental and biological samples. Most methods employ distillation, extraction, an optional cleanup step, concentration, and final separation by gas chromatography (GC). Use of the highly specific Thermal Energy Analyzer (TEA) as a GC detector affords simplification of sample handling and cleanup without sacrifice of selectivity or sensitivity. Mass spectrometry (MS) is usually employed to confirm the identity of nitrosamines. Utilization of the mass spectrometer s capability to provide quantitative data affords additional confirmatory evidence and quantitative confirmation should be a required criterion of environmental sample analysis. Artifactual formation of nitrosamines continues to be a problem, especially at low levels (0.1 to 1 ppb), and precautions must be taken, such as addition of sulfamic acid or other nitrosation inhibitors. The efficacy of measures for prevention of artifactual nitrosamine formation should be evaluated in each type of sample examined. 

Nitrogen-phosphorus detection PC = Photoconductivity TEA = Thermal energy analyzer UV = Ultraviolet detector... 

The oldest chemiluminescent detector was the thermal energy analyzer (TEA), which was specific for N-nitroso compounds. N-nitroso compounds such as nitrosamines are catalytically pyrolyzed and produce nitric oxide which reacts with ozone to produce nitrogen dioxide in the excited ] state, which decays to the ground state with the emission of a photon. A photomultiplier in the reaction chamber measures the emission. Nitrosodi-methylamines have been detected to about 30-40 pg [108]. 

The components in a mixture separate in the column and exit from the column at different times (retention times). As they exit, the detector registers the event and causes the event to be recorded as a peak on the chromatogram. A wide range of detector types are available and include ultraviolet adsorption, refractive index, thermal conductivity, flame ionization, fluorescence, electrochemical, electron capture, thermal energy analyzer, nitrogen-phosphorus. Other less common detectors include infrared, mass spectrometry, nuclear magnetic resonance, atomic absorption, plasma emission. 

See Chromatography, Appendix BA.) Use a gas chromatograph equipped with a Thermal Energy Analyzer detector (Thermo Electron Corporation, or equivalent) and a 1.8-m x 3-mm (od) stainless steel column, or equivalent, packed with 20% Carbowax 20M, or equivalent, and 2% sodium hydroxide on 80- to 100-mesh, acid-washed Chromosorb P, or equivalent. Maintain the column at 170°. Set the injector port temperature to 220°. Use argon as the carrier gas, with a flow rate of 25 to 30 mL/min. Operate with a -110° to -130° slush bath. Adjust instrument parameters such as vacuum chamber pressure, oxygen flow, and calibration knob to obtain the proper sensitivity. 

Procedure (See Chromatography, Appendix IIA.) Set attenuation (usually 4) of the chromatograph s thermal energy analyzer detector so that an injection of 30 pg of NDMA gives a definite peak with acceptable background. Using this attenuation, analyze 5- to 6-pL aliquots, in duplicate, of NDMA Standard Solutions of 5, 10, 20, and 40 ng/mL. (Note the volume injected.)... 

Based on animal studies, A-nitrosamines are compounds with proven carcinogenic effect. The search for sources and reduction of human exposure to their action is now one of the most important research problems. Currently, a major problem is the presence of A-nitrosamines and their precursors in food. Determination of A-nitrosamines in food relies on isolating these compounds by vacuum distillation in a basic medium, in the presence of liquid paraffin, followed by extraction with dichloromethane, pre-concentration of the sample, and analysis using GC. A thermal energy analyzer coupled to a gas chromatograph can serve as an efficient detector for these compounds. 

Two other types of element-specific detector for nitrogen currently in use coupled to SFCs are the nitrogen phosphorus detector (NPD) and the thermal energy analyzer (TEA). The NPD uses a hot, catalytically active solid surface immersed in a layer of dissociated H2 and O2 to form electronegative N and P ions which are detected on a nearby electrode [2]. NPD has been shown to have broad application in SFC, especially in the agrochemical industry [3]. The TEA, as described by Fine et al. [4], uses low-temperature pyrolysis, followed by ozone-induced chemiluminescence, for the detection of compounds containing NO2 groups. The TEA has been used for the determination of tobacco-specific nitrosamines and explosives [5]. Both of these detectors require spedlic standards of the analytes of interest for quantitation... 

The choice of detector is critical to the specific types of chemicals to be analyzed. Some units will detect everything and the output will resemble noise some will detect only certain types of chemicals. The latter type is preferred, and in the case of nitrosamines, the thermal energy analyzer/detector is the method of choice. Because smoke condensate is filthy, the cheaper, packed column is invariably used. Generally it gives adequate separation of the nitrosamines. 

GC = Gas chromatography MS = mass spectrometry HRGC = High resolution gas chromatography TEA = thermal energy analyzer MPO = nitrogen-phosphorus detector HECD = Hall electrolytic conductivity detector AFID = alkali flame ionization detector EC = electron capture detector NG = not given... 

A sensitive and selective chemiluminescent detector that has made an appreciable impact on the analysis of nitrosamines in environmental samples in the last several years is the thermal energy analyzer or (TEA) (15-19). This detector utilizes an initial pyrolysis reaction that cleaves nitrosamines at the N-NO bond to produce nitric oxide. Although earlier instrumentation involved the use of a catalytic pyrolysis chamber (15,17,19), in current instruments, pyrolysis takes place in a heated quartz tube without a catalyst (20). The nitric oxide is then detected by its chemiluminescent ion react with ozone. The sequence of reactions can be depicted in Figure 1. A schematic of the TEA is shown in Figure 2 (17). Samples are introduced into the pyrolysis chamber by direct injection or by interfacing the detector with a gas chromatograph (15,17,21,22) or a liquid chromatograph (22-25). 

Another capillary method specific for nitrosated pyridine alkaloids utilizes a thermal energy analyzer (TEA) detector (Peng 1990). The procedure for a 1-g sample is similar to that described above using an NPD except for the following ... 

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

Various GC methods have also been developed for the determination of nitrate, but the ions must be derivatized to achieve suitable volatility before GC analysis. Nitrate is commonly determined as nitrobenzene, which can be detected with an electron-capture detector or a thermal energy analyzer at levels of 0.05 or O.lpgmH, respectively. 

GC is used for the detection and identification of explosives, whether they are found as pure materials or postblast residues. According to Yinon and Zitrin, GC detectors suitable for the determination of explosives are the F.I.D., mass spectrometer (MS), electron capture detector (ECD), nitrogen-phosphorus detector (NPD), and thermal energy analyzer (TEA). The most selective detector is the TEA, which detects only compounds that produce NO or NO2. 

Because of the very high toxicity of NDMA, sensitive analytical methods (suitable for levels in parts per 10 range) have been developed, all involving GC separation. Various mass spectrometric detection strategies have been employed to overcome the problem of possible direet interferences at the low m/z values employed (moleeular mass of NMDA is 74 Da), as described below. Earlier methods (e.g. BUledeau 1987 Tomkins 1995) used GC with detection by the so-called thermal energy analyzer , which is in fact a GC detector based on a chemiluminescent reaction of ozone with nitric oxide (NO) produced... 

SIM selected ion monitoring TCD thermal conductivity detector TD thermal desorption TEA thermal energy analyzer TID thermionic detector /m retention time of solvent /r retention time of analyte a mobile phase velocity WCOT wall-coated open tubular a separation factor... 

Two of the more recently developed detectors, namely, the Hall electrolytic conductivity detector (ELCD) and the photoionization detector (PID) are recommended by the EPA for the analysis of volatile and semivolatile halogenated organic compounds and low molar mass aromatics. Chemical emission based detectors, such as the thermal energy analyzer (TEA) for its determination of... 

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