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The constants (K(s)) and enthalpies (DeltaH(s)) for stacking interactions between purine nucleoside monophosphates were determined by calorimetry; the values thus obtained were guanosine as follows: K(s) = 2.1 +/- 0.3 M(-)(1) and DeltaH(s) = -41.8 +/- 0.8 kJ/mol for adenosine 5'-monophosphate (5'AMP); K(s) = 1.5 +/- 0.3 M(-1) and DeltaH(s) = -42.0 +/- 1.5 kJ/mol for guanosine 5'-monophosphate (5'GMP); and K(s) = 1.0 +/- 0.2 M(-1) and DeltaH(s) = -42.3 +/- 1.1 kJ/mol for inosine 5'-monophosphate (5'IMP). The interaction of nickel(II) with purine nucleoside monophosphates was studied using potentiometric and calorimetric methods, with 0.1 M tetramethylammonium bromide as the background electrolyte, at 25 degrees C. The presence in solution of the complexes [Ni(5'GMP)(2)](2)(-) and [Ni(5'IMP)(2)](2)(-) was observed. The thermodynamic parameters obtained were log K(ML) = 3.04 +/- 0.02, log K(ML2) = 2.33 +/- 0.02, DeltaH(ML) = -18.4 +/- 0.9 kJ/mol and DeltaH(ML2) = -9.0 +/- 1.9 kJ/mol for 5'GMP; and log K(ML) = 2.91 +/- 0.01, log K(ML2) = 1.92 +/- 0.01, DeltaH(ML) = -16.2 +/- 0.9 kJ/mol and DeltaH(ML2) = -0.1 +/- 2.3 kJ/mol for 5'IMP. The relationships between complex enthalpies and the degree of macrochelation, as well as the stacking interaction between purine bases in the complexes are discussed in relation to previously reported calorimetric data.

A new way of implementing sequential injection analysis involving the use of the sample as a carrier is proposed. These systems are especially suitable for constructing continuous monitoring set-ups with no restrictions regarding the amount of sample which can be processed. A new standard addition methodology was used to calibrate the proposed system. The methodology was applied to the determination of Fe II with ophenanthroline (a reaction which involves a single reagent) and that of phosphorus by formation of a blue heteropolyacid (a reaction involving two reagents). The analysis rate is 8 min per sample (3 standard additions). The manifold design together with an adequate programme of aspiration-impulsion movements avoids the memory effects between samples. Determination of Fe II is linear between 0.25 and 6 mg l 21 Fe II . In the analysis of a sample containing 2.3 mg l 21 Fe II (n = 10) a relative standard deviation of 1.7% has been obtained. The detection limit (3s) is 0.06 mg l 21 Fe II and the determination limit (10s) 0.2 mg l 21 Fe II . Determination of P is linear between 0.1 and 1 mg l 21 P and in the analysis of a sample containing 0.75 mg l 21 P (n = 10) a relative standard deviation of 4.1% has been obtained. The detection limit is 0.02 mg l 21 P and the determination limit 0.1 mg l 21 . Both methods have been applied to the determination of Fe and P in spiked waters. The use of the methodology based on the standard addition has been evaluated in the case of P determination in order to eliminate interferences of the multiplicative type.