Determination of chloride, nitrate and calcium ions in sugar with ion selective‐electrodes

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Abstract
Chloride, nitrate, and calcium ion‐selective electrodes were tested and found satisfactory for the determination of the corresponding ions in highly refined white sugar, molasses and other impure sugar samples at different stages of sugar manufacturing or refining. The interferences by Br− and I− ions in Cl− determination were eliminated by oxidation with 3 M HNO3 and passing air to remove the free Br2 and I2 formed. The Cl− concentration was then determined with a chloride‐selective electrode against a calibration curve. Chloride should not be determined by ashing sugar, since this causes high losses of Cl−. It was found that NO3− and free Ca2+ ions could be determined directly in the sugar solution against corresponding calibration curves. Total calcium was determined after ashing of sugar samples. The ash was dissolved in 0.1 M HCl and passed through an anion exchange resin to remove PO3−4 and SiO2−3 ions, and Ca2+ was determined as before. Bound calcium was obtained by subtracting values of free from total calcium. Determination of bound calcium was useful to monitor the process of liming. For comparison, the three ions were also determined with acceptable precision without removing interfering ions using the method of standard addition and Gran's plot. The errors of determination for both direct and standard addition techniques were 3% for Cl− and NO−3 and 1–5% for Ca2+.

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