title: FIA-potentiometry in the sub-Nernstian response region for rapid and direct chloride assays in milk and in coconut water.
abstract: A simple and reliable FIA-potentiometric system for rapid assays of chloride in certain food samples is described and evaluated. The system is constituted by an aquarium air pump to propel the carrier solution, a manually operated injector, a homemade dialysis flow cell, a solid-state chloride detector (Ag/AgCl), a reference electrode and a multimeter connected to a microcomputer for data acquisition. The dialysis unit enables direct analysis of liquid food samples without any other previous treatment. The principal novelties are the precision (R.S.D. of 1.2% for whole milk) and rapidity (90 determinations/h) of FIA measurements near and below the lower end of the linear (Nernstian) response region of the chloride ion-selective electrode (ISE), with an estimated detection limit (3s) of 0.4mgL(-1) Cl(-) in the sample injected in donor stream. Data of peak potential versus sample chloride concentration (donor stream) was accurately fitted with a quadratic polynomial over the range between 4 and 1000mgL(-1) (r(2)=0.9999) and used as a calibration curve. The method was applied to the determination of chloride in milk and in coconut water samples. The validation of the results was done by comparison with a NIST reference material (milk) or by capillary electrophoresis (coconut water). For all analysis, no significant difference at a 95% confidence level was observed.
authors.affiliation: Departamento de Química, CCET, Universidade Federal do Maranhão, São Luís, MA, Brazil.
authors.forename: Iranaldo Santos
authors.initials: IS
authors.lastname: da Silva
authors.forename: Eduardo Mathias
authors.initials: EM
authors.lastname: Richter
authors.forename: Claudimir Lúcio
authors.initials: CL
authors.lastname: do Lago
authors.forename: Ivano G R
authors.initials: IG
authors.lastname: Gutz
authors.forename: Auro Atsushi
authors.initials: AA
authors.lastname: Tanaka
authors.forename: Lúcio
authors.initials: L
authors.lastname: Angnes