Use of a Ca-selective electrode in the determination of total Ca in the production of crude sugar. Preliminary studies

Uso de um eletrodo seletivo de cálcio na determinação do total de cálcio na produção de açúcar cristal. Estudos preliminares

Abstracts

The determination of the total calcium in juice, syrups, and other products of the sugar industry is investigated. Total calcium and free calcium is determinated by AAS and employing Ca-selective electrode respectively. A coefficient is obtained for the relation of total calcium with respect to free calcium. The coefficient is employed to determine the content of total calcium in accordance with the following equation.<img src="http:/img/fbpe/eq/v22/15e.gif" alt="15e.gif (673 bytes)" align="middle">

Ion-selective electrode; Ca-selective electrode; Atomic Absorption Spectrometry; sugar juice

Foi investigada a determinação do total de cálcio em sucos, melaços, xaropes e outros produtos da indústria açucareira. O cálcio total eo cálcio livre foram determinados, respectivamente, por espectroscopia de absorção atômica (AAS) e empregado eletrodo seletivo de cálcio. Foi obtido no coeficiente para relação entre o cálcio total e o cálcio livre. Este coeficiente foi utilizado na determinação do conteúdo total de cálcio, segundo equação:<img src="http:/img/fbpe/eq/v22/15p.gif" alt="15p.gif (761 bytes)" align="middle">

Eletrodo de íon seletivo; espectroscopia de absorção atômica; caldo de cana

Use of a Ca-selective electrode in the determination of total Ca in the production of crude sugar. Preliminary studies.

Jorge GONZÁLEZ GARCÍA^*

V.V EGONOV^**

Rubén DEL TÓRO DÉNIS^***

E. DEL TÓRO DÉNIS^***

S. MARTINÉZ SÁEZ^*

A. RAMOS VEGA^*

ABSTRACT: The determination of the total calcium in juice, syrups, and other products of the sugar industry is investigated. Total calcium and free calcium is determinated by AAS and employing Ca-selective electrode respectively. A coefficient is obtained for the relation of total calcium with respect to free calcium. The coefficient is employed to determine the content of total calcium in accordance with the following equation.

Ca (tot)

= K

Ca (free)

Relative error is less than 5 %.

KEYWORDS: Ion-selective electrode; Ca-selective electrode; Atomic Absorption Spectrometry; sugar juice.

Introduction

The use of a massive form of the Calcium ion-selective electrode in the sugar production process is limited by the existence in the sugared fluids, of other products not only free calcium, but also different compounds which contain calcium, eg. phosphates, organic acids, aminoacids and proteins.¹ This makes it impossible to give values of total calcium in juice, molasses in the sugar industry.⁵ The express analysis of the content of calcium by an ion-selective electrode (ISE) would be able to control the considerable presence of this element in different stages of the sugar production² process and so avoid scaling in equipment and apparatus and the loss of sugar in final molasses.^1,3

In our work we determine the relation between free calcium and total calcium in juices, molasses and crude sugar. We employ this relation to determine total content of calcium in the sample by ISE.

Materials and methods

In the realization of this study a calcium ion-selective electrode was prepared using an ether derivative of 1,2,3 trihydroxysulfonic acid mixed with polyvinylchloride and dissolved in cyclohexanone to make up a laminated matrix which is fixed to a plastic tube. The experiments were carried out at 298 ± 1K using a Ag/AgCl electrode as a reference electrode, which was to a digital milivoltmeter MV-88, whose error in measuring does not exceed 0.1 mV. The reagents used where CaCl₂, MgCl₂, Cyclohexanone, SnCl₂, all analytical grade and polyvinylchloride chromatographic grade.

The determination of the total calcium in the samples and model solutions were done in an atomic absorption spectrometer AAS-3 at a wavelenght of 422.7 nm.

Results and discussions

The elaborated calcium ion-selective electrode presented a electrochemical behavior in correspondence with Nernst relationships, can be used for describing electrode potentials ranging from 0.1 mol/L to 3.10^-6 mol/L with an average slope of 27.4 mV/decade close to the theoretical value for divalent ions. The electrode response was instantaneous with a maximum permissible potential deviation of ± 1mV.

For the determination of calcium in the samples taken from Panama sugar factory these were: Some juices of purifier, mixed juice, clarified juice, molasses and crude sugar. In the case of the concentrated syrup (molasses) and the crude sugar, the respective dilution of the solutions were made (5 and 10% w/r respectively).

The results were as follow:

The value of the average coefficient for juices and syrups is :

(1)

K_av = 1.497

This coefficient can serve as a base for calculation in the determination of the total calcium:

Ca _tot = K_av. Ca(free) (2)

By employing equation (2) the following results are obtained.

It can be clearly seen that between the average calculated values and the average values of total calcium (AAS), the relative error does not surpass 4%.

In the case of crude sugar the results calculated and those obtained by AAS, maintained the following correspondence.

Conclusions

The preliminary results obtained in our work permit in a very quick way to determine the concentration of total calcium in the production process of sugar by using an ion-selective electrode sensitive to calcium. Total concentration can be determined in an indirect manner based on the fact that it is possible to find a correlation coefficient that can be employed in the calculation of Ca(tot).

It’s necessary to reaffirm more than ever the validity of the methology used by increasing the determination in different stages of the year where the raw material changes its calcium compositions in dependence of characteristic of the juice.

GONZÁLEZ GARCÍA, J., EGONOV, V. V., DEL TÓRO DÉNIZ, E., MARTINÉZ SÁEZ, S., RAMOS VEGA, A. Uso de um eletrodo seletivo de cálcio na determinação do total de cálcio na produção de açúcar cristal. Estudos preliminares. Ecl. Quím (São Paulo), v.22, p.193-197, 1997.

RESUMO: Foi investigada a determinação do total de cálcio em sucos, melaços, xaropes e outros produtos da indústria açucareira. O cálcio total eo cálcio livre foram determinados, respectivamente, por espectroscopia de absorção atômica (AAS) e empregado eletrodo seletivo de cálcio. Foi obtido no coeficiente para relação entre o cálcio total e o cálcio livre. Este coeficiente foi utilizado na determinação do conteúdo total de cálcio, segundo equação:

Ca (total)

= K

Ca (livre)

Com um erro relativo menor que 5%.

PALAVRAS-CHAVE: Eletrodo de íon seletivo; espectroscopia de absorção atômica; caldo de cana.

Recebido em 17.5.1996.

Aceito em 12.9.1996.

** Bielorrussian University - Belarus.

*** Chemistry of Sugar Industry.

Average

• 1 DOBZHITZKI, Ya. Jimicheeski analiz V caxanroka proizrodstvie Moscow: Agropromizdat, 1985.
• 2 HONIG, P. Principios de técnología azucarera. CECSA, 1969, v.1.
• 3 KORYTA, J. Stulik en iontove-selektivni electrody. Moscow: MIR, 1989. p.221-6.
• 4 NOCEDO, A. G. Estudio preliminar de la desclarificación de jugos clarificados con zeolitas en el CAI Bolivia Camagüey, 1993. Thesis. Deparment of Chemistry. The University of Camagüey, Cuba.
• 5 RUZICKA, J. F. Glow injection analysis. Anal. Chem., v.55, n.11, p.1040-53 A, 1983.

*

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

Publication Dates

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

History

• Accepted
  12 Sept 1996
• Received
  17 May 1996