Thermal energy analyzer analysis

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. 

D. H. Fine, D. Lieb and F. Rufeh, Principle of operation of the thermal energy analyzer for the trace analysis of volatile and nonvolatile N-nitroso compounds. Journal of Chromatography, 1975,107(2), 351-357. 

Nitrosamines (Method 607). The nitrosamines are extracted with methylene chloride, treated with HC1, concentrated, and solvent exchanged to methanol for direct nitrogen-phosphorus or thermal energy analyzer (TEA) detection. Provision is made for Florisil or aluminum oxide column cleanup prior to GC analysis. The GC column liquid phase is 10 Carbowax 20 M plus 2 KOH. N-Nitrosodiphenylamine thermally degrades to diphenylamine in the GC and is measured as diphenylamine after prior removal of any diphenylamine occurring, as... 

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. 

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

Adams, J.D., K.D. Brunnemann, and D. Hoffmann Chemical studies on tobacco smoke. LXXV. Rapid method for the analysis of tobacco-specific A-nitrosamines by gas-liquid chromatography with a thermal energy analyzer J. Chromatography 256 (1983) 347-351. 

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

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). 

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. 

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... 

The classical nitrosamine analysis was performed for many years by gas chromatography using a thermal energy analyzer (TEA) as detector. This special TEA detector was used due to its selectivity for nitrosamines based on the specific chemiluminescent reaction of ozone with the detector generated NO from nitrosamines. Today, with increased sensitivity requirements, the detection limits of the TEA, and also its complex operation, do not comply any more with the required needs for low detection limits and sample throughput. Mass spectrometric methods have increasingly replaced the TEA. 

Fig. 1.5. Experimental setup of the high-frequency laser vaporization cluster ion source driven by a 100-Hz Nd Yag laser for the production of ion clusters, ion optics with a quadrupole deflector, and quadrupole mass Alter for size-selection and deposition the analysis chamber with a mass spectrometer for thermal desorption spectroscopy (TDS), a Fourier transform infrared spectrometer, a spherical electron energy analyzer for Auger electron spectroscopy (AES) for in situ characterization of the clusters [73]...

Krull et al (30) recently described rapid and reliable confirmatory methods for the thermal energy determination of N-nitroso compounds at trace levels. These approaches utilize minor modifications in the normal operation of the analyzer, GC and HPLC interfaced with the analyzer, UV irradiation of the sample and wet chemical procedures. Comparisons were made between these analyzer associated methods of confirmation and other approaches for the determination of N-nitroso compounds at trace levels. Figure 5 illustrates the analysis scheme by Krull et al (30) to distinguish N-NO compounds from C-NO, O-NO, N-NO2, C-NO2, and O-NO compounds utilizing the TEA analyzer. 

The use of GC for the analysis of GSR is limited due to the incompatibility of many of the analytes, such as the nitrate esters, and the lack of volatility of nitrocellulose, the major component of smokeless propellant. Despite this, GSR has been successfully analyzed using GC employing a variety of detectors including flame ionization, electron capture, and thermal energy analysis. Thermal energy analysis has been found to be particularly useful as it is selective for the nitro-containing compounds present in GSR. Recent attempts have been made to individualize GSR to a particular class of firearm and/or ammunition using chemometric techniques. 

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