The mineral composition of apples. XI. An extraction technique suitable for the rapid determination of calcium, but not potassium and magnesium, in the fruit

Practically all the calcium could be extracted from apple tissue, provided that particle size was reduced initially by a blending procedure, by heating with 6 N‐hydrochloric acid for 10 min. Tests with commercial samples indicated that including the time required to remove the seeds, a determination of calcium could be completed within 45 min of receiving a sample of 20 apples. Potassium, phosphorus and hydrochloric acid were the main factors interfering with the determination of 0.25 to 1.25 parts/million of calcium in solutions similar to those of apple ash or extracts by emission in a flame spectrophotometer. Average proportions of these and the other main constituents of the ash were added to standard calcium solutions to overcome interferences in routine analyses after dry ashing or extraction with hydrochloric acid. Recoveries of potassium and magnesium were low when the extraction procedure was used.