Nitrogen selectivity

Figure 8.62 shows the effect of temperature and of positive potential application on the reaction rates and on the nitrogen selectivity for the C3H6/N0/02 reaction.67,68 Electrochemical promotion significantly enhances both activity and N2 selectivity (e.g. from 58% to 92% at 350°C) and causes a pronounced (60°C) decrease in the light-off temperature of NO reduction in presence of 02. Positive potentials weaken the Rh=0 bond, decrease the O coverage and thus liberate surface sites for NO adsorption and dissociation. 

Figure 8.64. Transient effect of a constant negative applied potential on the on the rates of C02, N2 and N20 formation, on the NO conversion and nitrogen selectivity during NO reduction by CO on Rh/YSZ.69 Reprinted with permission from Elsevier Science.

Figure 8.67. Dependence of the nitrogen selectivity on the reaction temperature and on the catalyst potential for the chemically promoted Rh/YSZ catalyst C2.69 Reprinted with permission from Elsevier Science.

Auger electron spectroscopy Phosphorous/nitrogen-selective alkali/flame ionisation detector Atomic force microscopy Atomic fluorescence spectrometry All-glass heated inlet system... 

Marano RS, Levine SP, Harvey TM. 1978. Trace determination of subnanogram amounts of acrylonitrile in complex matrices by gas chromatography with a nitrogen-selective detector. Anal Chem 50 1948-1950. 

Thermal Energy Analysis and Nitrogen-Selective Detectors 381... 

Gas chromatography is one of the most powerful analytical techniques available for chemical analysis. Commercially available chemiluminescence detectors for GC include the FPD, the SCD, the thermal energy analysis (TEA) detector, and nitrogen-selective detectors. Highly sensitive detectors based on chemiluminescent reactions with F2 and active nitrogen also have been developed. 

The NO + 03 chemiluminescent reaction [Reactions (1-3)] is utilized in two commercially available GC detectors, the TEA detector, manufactured by Thermal Electric Corporation (Saddle Brook, NJ), and two nitrogen-selective detectors, manufactured by Thermal Electric Corporation and Antek Instruments, respectively. The TEA detector provides a highly sensitive and selective means of analyzing samples for A-nitrosamines, many of which are known carcinogens. These compounds can be found in such diverse matrices as foods, cosmetics, tobacco products, and environmental samples of soil and water. The TEA detector can also be used to quantify nitroaromatics. This class of compounds includes many explosives and various reactive intermediates used in the chemical industry [121]. Several nitroaromatics are known carcinogens, and are found as environmental contaminants. They have been repeatedly identified in organic aerosol particles, formed from the reaction of polycyclic aromatic hydrocarbons with atmospheric nitric acid at the particle surface [122-124], The TEA detector is extremely selective, which aids analyses in complex matrices, but also severely limits the number of potential applications for the detector [125-127],... 

Lehane, D.P. et al. 1976. Therapeutic drug monitoring Measurements of antiepileptic and barbiturate drug levels in blood by gas chromatography with nitrogen-selective detector. Ann Clin Lab Sci. 6 404. 

Af-methylation of the 3-amino-substituted THD 66 has been reported <2005JOC6230, 2005JMC2266>. Due to the calculated p-ATa s of the two nitrogens, selective methylation of the nitrogen attached to the THD nucleus is only possible for the synthesis of compound 214 via intermediate 213 in a two-step protocol (Scheme 13). 

Calverly and Denny [199] have described a rapid and sensitive procedure for the determination of residue levels of three uracil herbicides in soils. After addition of calcium hydroxide and Celite to the soil the herbicides are eluted from columns with water. After acidification of the eluate and partition into chloroform these herbicides are determined by gas chromatography using a nitrogen-selective detector. Recoveries from a range of soil types are better than 80%, with a sensitivity limit of 20pg kgy1. 

Carlsson H, Robertsson, G, Golmsjo. 2001. Response mechanisms of thermionic detectors with enhanced nitrogen selectivity. Anal Ghem 73 5698. 

Holt, R.F. Determination of hexazinone and metabolite residues using nitrogen-selective gas chromatography, J. Agric. Food CAem.,29(l) 165-172, 1981. 

An example of the use of GC with nitrogen selective detection is in the quantification of bupivacaine in plasma. Bupivacaine contains two nitrogen atoms in its structure which makes it a good candidate for this type of analysis. The limits of detection which can be achieved with a nitrogen selective detector for this compound are much better than methods based on flame ionisation detection, which are much less selective. 

Paputa-Peck, M. C., R. S. Marano, D. Schuetzle, T. L. Riley, C. V. Hampton, T. J. Prater, L. M. Skewes, T. E. Jensen, P. H. Ruehle, L. C. Bosch, and W. P. Duncan, Determination of Nitrated Polynuclear Aromatic Hydrocarbons in Particulate Extracts by Capillary Column Gas Chromatography with Nitrogen Selective Detection, Anal. Chem., 55, 1946-1954(1983). 

Figure 5. Glass capillary gas chromatogram of airborne aromatic amines in a film processing laboratory nitrogen selective detection. Peak identities 1, N,N-diethylaniline 2, 2,6-dimethylaniline (internal standard) 3, N,N-diethyl-1,4-di-aminobenzene 4, N,N -diisopropyl-1,4-diaminobenzene 5, not identified.

MS, Mass spectrometry El, electron impact Cl, chemical ionization MID, multiple ion detection PICI, positive-ion chemical ionization NICI, negative-ion chemical ionization SIM, selected ion nmonitoring TSP, thermospray PPINICI, pulsed positive ion-negative ion chemical ionization ECD, electron-capture detector NPD, nitrogen/phosphorous detector NSTD, nitrogen-selective thermionic detector FT-IR, Fourier transform infrared spectrometry. 

Gas chromatographic methods have been successfully used for the determination of penicillin molecules bearing neutral side-chains in milk and tissues (95, 97), but cannot be used for amphoteric -lactams. Gas chromatography of penicillin residues is further complicated by the necessity for derivatization with diazomethane. This derivatization step is particularly important because it not only leads to formation of the volatile penicillin methyl esters but also improves their chromatographic properties (thermal stability and decreased polarity). Using a fused-silica capillary column in connection with a thermionic nitrogen-selective detector, excellent separation and sensitivity figures were obtained. 

If the heterocyclic base contains several pyridine-type nitrogens select can also be observed. Indeno[l,2-b]quinoxalines, for example, are quaternized at the N-10 atom.110 The alkylation of heterocycles conta one pyrrole-type nitrogen and several pyridine-type nitrogens is appar selective (e.g., indolo[2,3-b]quinoxaline).201 The yields of quaternary however, are extremely low,201 even if phenacyl halides or a-halo ester used.207 Perhaps the resultant quaternary salts are dealkylated.200,207... 

The carboxin is extracted from the sample with acetone in a Soxhlet extraction apparatus and, after concentration of the extract, is determined via gas-liquid chromatography using a nitrogen-selective detector. The presence of carboxin is confirmed by the use of a sulfur flame photometric detector. Recoveries ranged from 73 to 80% (barley) and 73 to 78% (wheat). 

U.S. EPA Method TO7 describes the determination of N-nitrosodimethylamine in ambient air (U.S. EPA, 1986). The method is similar to the NIOSH method discussed above and uses Thermosorb/N as adsorbent. The air flow is 2 L/min and the sample volume recommended is 300 L air. The analyte is desorbed with methylene chloride and determined by GC/MS or an alternate selective GC system, such as TEA, HECD, or thermoionic nitrogen-selective detector. The latter detector and the TEA are more sensitive and selective than the other detectors. Therefore, the interference from other substances is minimal. Other nitrosamines in air may be determined in the same way. 

Figure 8.13 Calculated permeate vapor concentration for a vapor-permeable membrane with a vapor/nitrogen selectivity of 30 as a function of pressure ratio. The feed vapor concentration is 1 %. Below pressure ratios of about 10, separation is limited by the pressure ratio across the membrane. At pressure ratios above about 100, separation is limited by the membrane selectivity [36]...

---