Uses of nitrate ion sensitive electrodes

Usos de eletrodos sensíveis a íons nitrato

Uses of nitrate ion sensitive electrodes

Rubén DEL TÓRO DÉNIS^*

Ana María PEÓN ESPINOSA^*

Hubert DANDIE MARSHALLECK^*

Andres BROCAR ESTEVEZ^*

ABSTRACT: Some models of ion-selective electrodes (ISE) and other methods have been elaborated, to quantify nitrate levels in environmental samples (water, fruits, vegetables and others), using direct potentiometry

KEYWORDS: Ion-selective electrods; direct potentiometry; nitrate concentration.

Introduction

The world wide specialized literature has reported in the last few years a human's life injure due to nitrate contamination.^1,6

Such dangerous effect has been revealed in different environmental samples, such as fruits, vegetables and other food.³

It's kown for example, that water well is quite often one of the more contaminated source in the field, causing serious health problems mainly in the infant population.^2,5,8

Our Department has been assigned the task of determining the ion nitrate concentration by using Ion-Selective Electrodes (ISE).

To this end, we have elaborated some models of Ion-Selective Electrodes and other methods in order to quantify nitrate level in environmental samples.

Experimental

For the determination of nitrate contents in various environmental samples (waters, fruits, vegetables, and other), it has been developed a nitrate sensitive electrode with a plastificated membrane (PVC-Membrane): Direct Contact, electrodes with internal reference solution and other different electrode variants and their methodologies.^4,7,9,10

It has been used as electrode active substance a high weight molecular quaternary ammonium nitrate inmovilized in PVC-Matrix with adequate plastificant.

The measurements system used is formed by an ion selective indicator electrode and the Ag/AgCl reference electrode linked to a milivolt-meter, pH-meter, ionometer (digital or analogical one), reflecting the dependence of pNO₃ vs E(mv) in correspondence with the Nernst Equation. In the practical use of the electrode, it's necessary the use of a buffer solution for the ionic strength regulation. It could be shown as the most notable interference the HCO₃, Cl, Br, anions of organic acids; I, MnO₄ and other.

Results and discussions

These electrodes show a lineal dependence between 0.1 and 1.10^-5 mol L^-1 with a slope of 56 + 3 mV next to the teoric value at 298 + 1 K being the electrode response practically instant. The minimum limit of detection is approximately 8.10^-6 mol L^-1. The probable interference was studied and the value of the potentiometric selectibility coefficient respect to Cl^–, HCO₃^– , B_r^–, NO₂, ClO₄, is quite similar to the values reported by foreign firms.

The error in the determination of nitrates by direct potentiometry was compared with Brucine Method and UV (Table 1, 2). The interference effect of the Cl^– and HCO₃ ions present frequently in water was deeply studied, showing how in the practical fulfillment of the analysis, it should have been avoided first by the elimination of the hydrogen carbonate at pH 3, and the subsequent increment by the addition on nitrate to the sample (Figure 1).

Electrodes made at the Chemistry Department in the University of Camagüey have been employed in the determination of nitrates in potatoes, onions, carrots and green tomatoes. The statistical analysis was carried out. Test of Hypothesis between two media sample with unknown (p = 95%) using different methodologies has been done (Table 3).

Conclusions

We have elaborated electrodes of different variants for determination of nitrate concentration by direct potentiometry. The effectivity of these dispositives is demonstrated in the control of content of nitrates in diverse surrounding samples, which allows its diffusion in different branches of economy public health and high education.

DEL TÓRO DÉNIZ, R., PEÓN ESPINOSA, A. M., DANDIE MARSHALLECK, H., BROCAR ESTEVEZ, A. Usos de eletrodos sensíveis a íons nitrato. Ecl. Quím. (São Paulo), v.22, p.205-210, 1997.

RESUMO: Alguns modelos de eletrodos de íon seletivo e outros métodos foram elaborados para determinar os níveis de nitrato em amostras de água, frutas, vegetais e outros, usando potenciometria direta.

PALAVRAS-CHAVE: Eletrodos de íon seletivo; potenciometria direta; concentração de nitrato.

Recebido em 10.6.1996.

Aceito em 25.9.1996.

• 1 FAN, A. M., WILLHIPE, C. C., BOOKS, S. A. Evaluation of the nitrate drinking water standard with reference to infant methemoglobinemia an potential reproductive toxicity. Regul. Toxicolog. and Pharmacology, v.7, p.135-48, 1987.
• 2 GARCÍA, D. P. Thesis. Department of Chemistry. University of Camagüey. Cuba, 1985
• 3 HOTCHKISS, J. H, CANSSENS , R. G. Nitrite, nitrate and nitroso compouns in foods. Food technology, v.41, p.127-35, 1987.
• 4 IGOROF, V. E. I. S. Conference University of Camagüey, Cuba, 1990.
• 5 KEATING J. P. et al. Infantile methemoglobinemia caused by carrot juice. Eng. J. Med., n.288, p.824-6, 1973.
• 6 LUCA, D. Cytogenetic changes induced in vivo by exposure to sodium nitrate. Rev. Med. Chin., v.41, n.2, p.305-7, 1987.
• 7 RAJMANKO, E. M., GULIEBICH, A. L. Potentiometry Minsk, Bielorrus, 1989. p.80.
• 8 SINIUS, V. A. Spinach toxicity in children.  Med. Wochenschv (Deutsch), n.90, p.1856-63, 1965.
• 9 SOLSHY, R. L. Analitical Chemistry, v.60, p.106-12, 1988.
• 10 WILLARD, H., MERRITT, L., DEANS, J. Instrumental methods of analisys Mexico: CECSA, 1987, p.600-25.

*

Department of Chemistry - University of Camagüey - Apdo 5372 - Zona Postal 3 - Camagüey - Cuba.

Publication Dates

• Publication in this collection
  22 May 2000
• Date of issue
  1997

History

• Accepted
  25 Sept 1996
• Received
  10 June 1996