High-sensitivity Determination Relationship of Sample Volume to Peak Height

6 HIGH-SENSITIVITY DETERMINATION RELATIONSHIP OF SAMPLE VOLUME TO PEAK HEIGHT 

Manifold Fig. 6.4a, where the injection valve is the type furnished with an external, interchangeable sample loop (Section 5.1). The following sample volumes are used (the number in parantheses denoting the corresponding lengths in cm of 1.14 mm tubing except for the smallest volume, where a 0.7-mm-ID tube is used) 23 xL (6.0) 70 fxL (6.9) 115 xL (11.3) 180 p.L (17.6) and 320 p.L (31.3). 

Reagents Molybdate solution 0.0025 M ammonium heptamolybdate (3.0897 g/liter) in 0.2 M nitric acid. Ascorbic acid solution 0.25% (w/v) in 10% (v/v) aqueous glycerine solution. 

Standard Solutions Standard solutions in the range 0-2 ppm P-PO4 are prepared by successive dilutions of the 100 ppm stock solution described in the preceding exercise. 

Exercise The analytical procedure is identical to that described in Section 6.5. However, as the manifold here is designed for high-sensitivity measurements of phosphate, large sample volumes are injected. Therefore, a manifold such as that shown in Fig. 63a cannot be used, as this would result in insufficient mixing and formation of double peaks (see Fig. 6.6).  

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