Characterization and in vitro sensitivity of cholinesterases of gilthead seabream (Sparus aurata) to organophosphate pesticides.

The characterization of cholinesterase activity in brain and muscle of gilthead seabream was carried out using four specific substrates and three selective inhibitors. In addition, K m and V max were calculated from the Michaelis-Menten equation for ASCh and BSCh substrates. Finally, the in vitro sensitivity of brain and muscle cholinesterases to three organophosphates (OPs) was also investigated by estimating inhibition kinetics. The results indicate that AChE is the enzyme present in the brain, whereas in muscle, a typical AChE form is present along with an atypical form of BChE. Very low ChE activity was found in plasma with all substrates used. The inhibitory potency of the studied OPs on brain and muscle AChEs based on bimolecular inhibition constants (k i ) was: omethoate < dichlorvos < azinphosmethyl-oxon. Furthermore, muscle BChE was found to be several orders of magnitude (from 2 to 4) more sensitive than brain and muscle AChE inhibition by dichlorvos and omethoate.

Reverse flow-injection manifold for spectrofluorimetric determination of aluminum in drinking water.

A simple reverse flow-injection (rFIA) manifold for the direct determination of aluminum in drinking water is proposed. This rapid and sensitive method is based on the formation of an Al(3+) complex with salicylaldehyde picolinoylhydrazone (SAPH), which shows a maximum blue-green fluorescence (lambda(ex)=384 nm, lambda(em)= 468 nm) at pH 5.4. Operative conditions both for batch and rFIA procedures were investigated including reagent concentration, buffer solutions, injection loop, reacting coil and wavelengths used for the fluorimetric detection. The tolerance limits of foreign ions have been also evaluated, before and after the addition of masking agents. The reverse flow-injection procedure allows determination of Al(3+) at ppb level (LOD: 1.9 mug l(-1)) within a working range of 5-30 mug l(-1). The proposed method was successfully employed for the determination of Al(3+) in several commercial drinking, soft drinking (as certified reference material), and tap water samples.

Fluorimetric determination traces of aluminium in soil extracts.

Salicylaldehyde picolinoylhydrazone (SAPH) form a fluorescent complex with aluminium (lambda(ex) = 384 nm, lambda(em) = 468 nm) in acidic medium (stoichiometry 1:3, Al:SAPH). Two procedures based on the direct or standard additions methods has been proposed for the determination of concentrations down to 1-2 mug/dm(3) of Al(III). The effects of 72 ions in the method has been evaluated and different masking agent reactions have been tested. The method has been used satisfactorily for the determination of aluminium at a level of mug/dm(3) in acetate extracts of several agricultural soils. The method has been compared favourably with ICP spectroscopy emission.