FIA-potentiometry in the sub-Nernstian response region for rapid and direct chloride assays in milk and in coconut water |
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Authors: | da Silva Iranaldo Santos Richter Eduardo Mathias do Lago Claudimir Lúcio Gutz Ivano G R Tanaka Auro Atsushi Angnes Lúcio |
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Institution: | a Departamento de Química, CCET, Universidade Federal do Maranhão, São Luís, MA, Brazil b Departamento de Química Fundamental, IQ, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, 05508900 Sao Paulo, SP, Brazil |
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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 (3 s) of 0.4 mg L−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 1000 mg L−1 (r2 = 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. |
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Keywords: | Chloride ISE FIA In-line dialysis Sub-Nernstian response Milk analysis Coconut water analysis |
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