Hydrogen trace analysis

Ultra-trace analysis, hydrogen peroxide determination, 638 Ultraviolet see UV Uncatalyzed sulfoxidations, 472-4 Uncertainty, analytical methods, 624 UN Environment Programme (UNEP) chemicals safety, 745, 747 SIDS database, 622 UnfunctionaUzed olefins... 

Tolg, G., and K, Ballschmiler Studies on Ultramicro- and Trace Analysis of Organic Substances. VI. Determination of Hydrogen in Nonvolatile Organic Compounds with 10—40 p.g of Substance. Microchem. J. 9, 257 (1965). 

When first put into use—and every few months thereafter— the flow conditions for optimum response of the FID should be determined. This can be done by the time-honored method of repeated injections while varying the flow rate of air and especially of hydrogen or by a faster method recently publicized (18). This test takes but a few minutes to execute but can improve analytical results considerably. To even mention FID optimization may well be redundant. It has been my experience, however, that most gas chromatographs equipped with flame ionization detectors are run under less than ideal flow conditions. In trace analysis, this oversight may be crucial. 

The sulfide generated by the first two reactions can be detected with a high degree of sensitivity, making this approach particularly valuable for trace analysis. Many laboratories do not like to use hydrogen or to work with relatively toxic H2S and therefore the reduction procedures are not widely used. 

Note that direct elution analysis of carbon dioxide even in large samples (25 ml) fails to determine trace hydrocarbons without concentration. The method may be recommended for the trace analysis of other acid gases (e.g., hydrogen sulphide, hydrocyanic acid). A chemical concentration method based on removal of unsaturated gaseous hydrocarbons (main component) for determination of trace amounts of hydrogen and carbon dioxide was developed by Alekseeva and co-workers [56, 57]. For absorption of olefins use was made of a column containing a solution of silver nitrate and mercury salts. 

Phase-transfer-catalyzed alkylation provides an excellent analytical approach for many polar active hydrogen compounds. The perceived advantages of the method for the trace analysis of polar CYA are the relative simplicity, the low detection limits, and the absence of interferences. Furthermore, the reaction conditions, although harsh, leave the molecule intact during the analysis, providing convenient identification by gas chromatography/mass spectrometry (GC/MS). It was seen that the detection limits for CYA between MS-SIM and FTD differed by 2 orders of... 

Jacobsson and Falk [56] suggested determination of low (ng/ml) concentrations of hydrogen sulfide in aqueous solutions with ALOT column (PoraPLOT Q). The detection limit is about 1 ng/ml (see Fig. 2-11 [56]). If greater sensitivity is needed stripping analysis in combination with a cryogenic focusing device should be used. A prerequisite of such a method, however, is that water has to be removed prior to the trap (for example, by calcium chloride [57]) in order to prevent plugging of the cold trap. Thus, ALOT columns can be recommended for trace analysis of polar compounds. 

Figure 10.146 Trace analysis of anions in 35% hydrogen peroxide solution after matrix elimination. Separator column lonPac ASH eluent (A) SOmmol/L NaOH and (B) water gradient 3% A for 3 min isocratic and then linearly to 80% A in 13 min flow rate ...

A chromatogram illustrating the use of a longer O C silicone oil column (40 feet) for trace analysis of hydrogen chloride in diborane is given in Figure 33. 

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