Quantitative Analysis Using Flow Injection Technique

6 Quantitative Analysis Using Flow Injection Technique [13] 

The complete system can be controlled by a computer with special software designed for this type of analysis and is available from PS Analytical (UK) as a Touchstone Package (PSA 30.0). The carrier liquid and sample plug is transported using a multiroller peristaltic pump at a rate predetermined to suit the analysis of interest. Silicone tubing of 0.8 to 1.0 mm internal diameter is normally used and is found to be best for most organic solvents. A sample loop used for injection is usually in the volume range of 150 to 500 pi with an internal diameter 0.8-1.0 mm and is made of solvent resistant plastic. The best volume of loop is predetermined for a particular sample and analyte concentration. 

A precision-controlled flow injection valve is necessary to keep the dispersion to a minimum and to keep the volume low and constant. A Teflon six port valve (obtained from PS Analytical, Orpington, UK, Cat No. PSA 60.00) was found to be the best. The ports are used for the loop, carrier stream, plasma supply and waste. The valve is controlled by the Touchstone Package . 

The FI valve is connected after the pump and as near possible to the nebuliser to reduce as much of the dispersion of the sample as possible. In normal analysis 15-20 s washout times should be sufficient between each injection to minimise memory effects, particularly for elements such as Mo, Ag, B and W. 

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Up to this point, the detection Unfit and sensitivity comparisons of the different sources have focused primarily on compoimds that ionize efficiently with all the techniques. It is important to understand the coverage or scope of an ionization technique across the chemical space of general interest, particularly when confronted with unknown compounds, or compounds whose structures are known but whose ionization properties have not been tested, and there is no time to assess a variety of options. This situation occurs in many drug discovery laboratories measuring in vitro ADME properties (administration, distribution, metabolism, excretion) where many different chemical species need to be assayed quickly. The data used to generate the relative efficiency values within a source in Tables 1-3 were used to calculate the relative MRM efficiency between the three sources and are shown in Table 13.4. The MALDI data were acquired in the most practical fashion to obtain a quantitative measurement where only a small percentage of the sample spot was ablated with a single raster. The ESI and APCI data were obtained by flow injection analysis at 200 and lOOOpL/min, respectively. Electrospray is the most sensitive ion source in nearly all... 

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