Nitrogen detection mode

Nitrophenols in fog and atmospheric particles were determined by GC of the underiva-tized compounds and their corresponding acetate esters. Four fused-silica columns were used with three alternative detection modes, namely mass-selective detection, nitrogen-specific detection and ECD. GC-ECD of the acetate derivatives gave the best results501. A capillary GC-UVD method was developed for the determination of small amounts of nitrophenols present in the environment. The method was compared with HPLC-UVD from the point of view of selectivity and sensitivity. LOD for GC were about one-tenth of those for HPLC502. 

Gas chromatography The AOAC method for the analysis of caffeine by GC uses a packed glass column, 6 ft ( 180 cm) in length by 4 mm ID, packed with 10% DC-200 oil on 80-100 mesh Gas Chrom Q, using nitrogen carrier gas and a thermionic potassium chloride detector. The injector temperature is 220°C, the column temperature is 190°C, and the detector temperature is 220°C. A wide variety of column-packing materials and detection modes can be used. For example, separation of caffeine, theophylline, and theobromine can be achieved with... 

There are three principal detection modes in commercial detectors halogen mode to detect HX, sulfur mode for delecting SO2 or SO3, and nitrogen mode for detecting NH3. The detector response depends on the reaction conditions, the solvent, the pH, and the use of a postreaction scrubber. A schematic representation of a commercially available detector unit is shown in Figure 6.28. 

As microwave sample preparation has evolved, standard microwave procedures have been developed and approved by numerous standard methods organisations (ASTM, AOAC International, EPA, etc.), see ref. [64]. Examples are standard test methods for carbon black/ash content (ASTM Method D 1506-97), lead analysis in direct paint samples (ASTM Method E 1645-94), etc. Table 8.15 shows some microwave ashing references (detection weight). A French AFNOR method utilises the atmospheric pressure single-mode microwave method as an alternative sample preparation procedure for Kjeldahl nitrogen determination [84], The performance of a microwave-assisted decomposition for rapid determination of glass fibre content in plastics for QC has been described [85]. 

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