Membrane sampler for interference-free flow injection NO determination in biological fluids with chemiluminescence detection

Abstract The development of a chemiluminescence (CL) method based on the perm-selective properties of a Nafion-cellulose acetate (CA) composite membrane for the monitoring of nitric oxide (NO) in biological fluids is described. Horseradish peroxidase (HRP) was used as NO trapping solution, forming the stable compound HRP-NO. The HRP was denatured and the trapped NO was released and detected by using the luminol-H 2 O 2 system. Using a mixed (size-exclusion and polar-based) transport control, the interference effects of various compounds were minimized. The method was used for NO monitoring in simulated samples, by using a blood specimen as sample matrix. The 3σ detection limit is 0.9 × 10 −6 mol and linear semi-log calibration plot in the range 1.8 × 10 −6 to 2.7 × 10 −3 mol NO was constructed. The applied methodology was further used to prolong the NO lifetime in order to increase the sensitivity of its determination. This was based on the increase of the response in the presence of certain reductive species, which act as NO preservatives in biological fluid samples

Reagentless enzyme electrode for malate based on modified polymeric membranes

Abstract A series of polymeric membranes have been employed as outer barriers in an amperometric malate dehydrogenase (MDH)/diaphorase (DI) or MDH/DI/NAD + /mediator enzyme electrode for the determination of malate in undiluted neutral or acidic media. MDH/DI were physically entrapped with NAD + and mediator in a mixed ester cellulose membrane. Outer membranes such as non-anionic surfactant-modified cellulose acetate/Tween-80 and unplasticised spin coated PVC/polycarbonate (PC) resin in conjunction with an ascorbate oxidase (AOD) layer were utilised. Mechanical strength, thickness studies and diffusional properties of the membranes were investigated. Hexacyanoferrate(III), 2,4-dichlorophenolindophenol (DCPI) and naphthoquinone (NQ) were tested as mediators for enzymatically produced NADH using cyclic voltammetry. Analytical utility of the sensors is demonstrated

Construction of a Triphenyltetrazolium Liquid Membrane Ion Selective Electrode and its Analytical Application to the Assay of Vitamin C

Abstract. The construction of a liquid triphenyltetrazolium cation (TT ) ion-selective electrode (ISE) based on [TT ] 3 [P(W 3 O 10 ) 4 ] salt dissolved in 2-nitrotoluene is described. The liquid membrane electrode exhibits a rapid and almost Nernstian response to triphenyltetrazolium cations in the concentration range from 2 Â 10 À4 to 1 Â 10 À2 mol l À1 . The Nernstian slope is 56±58 mV decade À1 which remains constant for at least two months. The response is virtually unaffected by pH changes in the range 3±12. Major interferents are periodate and malate. Deviation from linearity is also observed in the presence of bromide, iodide and thiocyanate, due to their precipitation with triphenyltetrazolium cations. Analytical applications such as direct potentiometry for the determination of TT in aqueous solutions and indirect potentiometry for the assay of ascorbic acid (vitamin C) in pharmaceutical preparations are described. Ascorbic acid in the range of 150±500 mg l À1 , under speci®ed experimental conditions, can be determined with mean relative error of 1.9%