Carrier Scavenger Pulse internal Detector temperature Sample size Retention time
0.5 ml, 5.0 ml 02, 1.6 min; NO, 1.6 min; NO2, 2.3 min
Reproduced with permission from Chromatography of Environmental Hazards. Copyright 1973, Elsevier Science.
column, or preferentially by direct injection of NO2. Tables 9.4 and 9.5 give the experimental conditions required for NO and NOX analysis.
Phillips and Coyne108 separated NO and NO2 in a variety of nitrogen containing organic compounds using a 6-ft column packed with 25% dinonylphthlate on Chromosorb B at 110oC with a hydrogen flow of 60 ml/min. The nitric oxide was quantitatively scrubbed out of the sample gas by acidified ferrous sulfate and determined by difference from samples.
Nitrous oxide (N2O) usually occurs in low concentrations. It is a normal constituent of both unpolluted atmosphere as well as seawater. N2O is formed upon decomposition of nitrogen containing inorganic and organic substances, and is also found in tobacco smoke. It is also used as an anesthetic in dental practice and in surgery. Commercially, heating pure ammonium nitrate to a temp of 245 to 270°C and allowing dissociating exothermically produces nitrous oxide.
Von Oettingen109 and Parbrook110 have cited the toxicity of nitrous oxide. Nitrous acid has been shown to be lethal to chick embryos, and teratogenic in rat and chick embryos. The effect of N2O on RNA and DNA of rat bone marrow and thymus has also been described by Green.111 A method was described by Buford112 for quantitatively analyzing gaseous mixtures of N2, N2O, CO2, A, and 02 by gas chromatography using three columns of molecular sieve material at elevated ambient and subambient temperatures; with simple modifications, the analysis time of 5 min could be reduced, which is shown in Figure 9.19. The columns all of 3 mm i.d. were packed with Linde molecular sieves. The high temperature (HT) column contained molecular sieve 5 A flour (<270 mesh) with non-acid-washed 60 to 80 mesh Chromosorb,113 the medium temperature (MT) column molecular sieve 13 X (32 to 60 mesh). The HT, MT, and low temperature (LT) columns were 225, 38, and 75 cm long, respectively, and all packing were activated by drying in air at 1050C (16 h) and 350°C (40 h) after the columns had been packed. A Shimadzu GC-IC
gas chromatograph was used with a thermal conductivity detector operated at 220°C, a bridge current of 100 mA and a recorder of 1 mV range. The carrier gas was helium with an inlet pressure of 3 kg/cm2 and an outlet flow of 75 ml/min. Temperatures were controlled by using the column oven at 146°C (HT column), a water bath at 25°C (MT column), and freezing methanol bath at -98°C (LT column).
Gas absorption chromatography was used by Rozenberg et al.114 to determine nitrous oxide in a mixture with nitrogen or nitric oxide. Silica gel KSK-2.5 (0.25 to 0.5 mm) heated preliminarily for 3 h at 350°C was used as the adsorbent. The analysis was performed using a column 163 X 3 mm2, a valve that gave precise regulation of the gas flow, a monometer, flow meter, sampling apparatus, a katharometer, and automatic recorder. The flow rate of hydrogen gas was 30 ml/min.
Bock and Schutz115 analyzed N2O in air by an initial collection on molecular sieve 5 A at room temperature, desorption at reduced pressure at 250 and 300°C, and finally determination by gas chromatography. An F&M Model 720 gas chromatograph was used with a thermal conductivity detector and a 1 m X 4 mm column containing molecular sieve 5 A (Type 0.5 to 0.91, Perkin Elmer, Bodenserwerk) with helium carrier gas at 50 ml/min.
Bennett116 described the use of two columns in series to affect complete separation of oxygen, nitrogen, methane, CO2, and nitrous oxide. The first was packed with porous polymer beads and the second with molecular sieve 5 A. A length of copper tubing between the columns enabled the gases that were separated on column I to be eluted before any emerge from column II. Column I was a 2 ft 3 in. length of 0.25 in. o.d. copper tubing filled with 50 to 80 mesh Porapak Q. The delay coil was a 7 ft X 0.25-in. o.d. copper tubing housed in the detector oven. Column II was a 6 ft X 0.25-in. o.d. copper tubing packed with 30 to 60 mesh molecular sieves 5 A, which was activated prior to packing by heating at 2500 for 4 h under vacuum. A Gow-Mac type 9235 Thermal conductivity cell fitted with SS-W2 filaments was used in conjunction with a Gas Chromatography RY 100 bridge unit. The resolution of nitrogen oxides with other gas is shown in Figure 9.20. The resolution of mixtures of CO2 and N2O was effected by Degrazio117 using a two-column system. An I&M Model
figure 9.20 Gas chromatographic separation of methane, nitrogen, oxygen, nitrous oxide, and carbon dioxide obtained using Porapak Q and molecular sieve 5 A columns in series. (Reproduced with permission from Chromatography of Environmental Hazards. Copyright 1973, Elsevier Science.)
720 gas chromatograph with a thermal conductivity detector was used with a small 4 in. precolumn insert of Linde Molecular sieve 13X connected with a 0.25-in. Swagelock union to a 6 ft X 0.25-in. o.d. stainless steel column packed with 30 to 60 mesh silica gel. The chromatographic conditions used for the resolution of C02 and N2O were: column, detector, and injection port temperatures, respectively: helium carrier gas flow at 26 ml/min.
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