SOP: Determination of Inorganic Constituents in Sugar (Lead, Copper and Arsenic)

GIFSQ — Global Institute for Food Safety & Quality

Principle

Lead, copper and arsenic in sugar are determined after sugar-specific sample preparation; the final estimation of each element is carried out by the method given in Chapter 6 of the book. For refined sugar, lead is separated directly from the dissolved sample; for raw or low-grade sugar the organic matter is first eliminated by ashing with magnesium nitrate. Copper is determined by the diethyldithiocarbamate method, and arsenic, after wet digestion, by the molybdenum-blue colorimetric method (the CAC/RS 4-1969 recommended method is the AOAC colorimetric method using silver diethyldithiocarbamate reagent).

Apparatus required

• 100-ml separating funnel
• 250-ml separating funnel
• Beaker
• Water bath

Reagents

a. Lead-free water.

b. Concentrated hydrochloric acid.

c. 10% solution of AR magnesium nitrate (for ashing raw or low-grade sugar).

Procedure — Lead in refined sugar

Weigh 10 g of sugar, dissolve in 20 ml of lead-free water in a beaker, and transfer to a 100-ml separating funnel using 5 ml of water

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Acidify with 2.5 ml of concentrated HCl

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Prepare a blank by adding 2.5 ml of concentrated HCl to 25 ml of water

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Estimate the lead by the method given in Chapter 6 of the book, using separation method I

Procedure — Lead in raw or low-grade sugar

To 5 g of sample add 10 ml of 10% solution of AR magnesium nitrate; evaporate to dryness and ash at a temperature not exceeding 500°C (ashing eliminates the organic matter)

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Dissolve the ash in 1 ml of concentrated HCl, add 25 ml of lead-free water, and heat on a water bath for 15 min

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Proceed for the estimation of lead as for refined sugar

Procedure — Copper

Weigh accurately 25 g of refined sugar, or 5–15 g of raw sugar

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Transfer quantitatively to a 250-ml separating funnel

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Proceed for the estimation of copper by the diethyldithiocarbamate method given in Chapter 6 of the book

Procedure — Arsenic

Digest the sample by wet digestion

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Determine the arsenic by the molybdenum-blue colorimetric method given in Chapter 6 of the book (according to CAC/RS 4-1969, the recommended method is the AOAC colorimetric method using silver diethyldithiocarbamate reagent)

Calculation

Report the lead, copper and arsenic contents as determined by the respective Chapter 6 methods, expressed in ppm.

Note: the full estimation procedures are given in Chapter 6 of the book (lead: pages 137 and 157, separation method I; copper: page 131, diethyldithiocarbamate method); this SOP documents the sugar-specific sample preparation exactly as the book gives it.

Precautions

• Use lead-free water for the lead determination.
• Do not exceed 500°C when ashing the raw or low-grade sugar sample for lead.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.

Recommended International Standards for White Sugar CAC/RS 4-1969, Joint FAO/WHO Food Standards Programme, Rome — cited in the book.

Official Methods of Analysis, Association of the Official Analytical Chemists, 12th edn, 1975 — cited in the book.