Flow injection analysis sample volume influence

The injected sample volume is by far the most important parameter affecting dispersion in flow injection analysis, as it has a pronounced influence on the height, width and area of the recorded peak (Fig. 5.11). 

FIGURE 5.17 Influence of the site of confluent stream addition, x = distance between injection port and confluence site A = peak height absorbance a, b = 25 and 1250 pL sample injected volumes. Other experimental conditions as in Ref. [84]. Adapted from Anal. Chim. Acta 198 (1987) 153, E.A.G. Zagatto, B.F. Reis, M. Martinelli, F.J. Krug, H. Bergamin-Filho, M.F. Gine, Confluent streams in flow injection analysis, with permission from Elsevier. 

The attractive features of splitless injection techniques are that they allow the analysis of dilute samples without preconcentration (trace analysis) and the analysis of dirty samples, since the injector is easily dismantled for cleaning. Success with individual samples, however, depends on the selection of experimental variables of which the most important sample size, sample solvent, syringe position, sampling time, initial column temperature, injection temperature and carrier gas flow rate, often must be optimized by trial and error. These conditions, once established, are not necessarily transferable to another splitless injector of a different design. Also, the absolute accuracy of retention times in splitless injection is generally less than that found for split injection. For splitless injection the reproducibility of retention times depends not only on chromatographic interactions but also on the reproducibility of the sampling period and the evaporation time of the solvent in the column inlet, if solvent effects (section 3.5.6.2) are employed. The choice of solvent, volume injected and the constancy of thermal zones will all influence retention time precision beyond those for split injection. For quantitative analysis the precision of repeated sample injections is normally acceptable but the method is subject to numerous systematic errors that may... 

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