Ionselective minielectrode determination of ionic and total calcium concentrations in mixed saliva

A minielectrode suitable for determination of ionized and total calcium in small volumes (5 microliters or less) of biological fluids without loss of carbon dioxide from the sample, was evaluated. The relative standard deviation ranged from 4.5-7.1%, and analytical recovery from 97-101%. Interference by hydrogen, sodium and magnesium was negligible. Small differences in ionic strength between standards and samples caused only minor analytical errors. Freezing the sample prior to analysis significantly affected the readings for ionized calcium concentration. Compared to determination by atomic absorption spectrophotometry, there was no statistical difference in the total calcium concentration of mixed saliva determined by the electrode at approximately pH 4 after addition of a known volume of hydrogen chloride. This minielectrode method evaluated allows accurate calcium analysis of fluids such as secretion from minor salivary glands or the fluid in the dental integument, with subsequent recovery of the sample for further analysis.