Ionized calcium in human milk determined with a calcium-selective electrode

Area of Science:

• Biochemistry
• Human Nutrition
• Analytical Chemistry

Background:

• Accurate measurement of ionized calcium (Ca2+) in human milk is essential for understanding infant nutrition.
• Standard methods for Ca2+ analysis are often optimized for blood plasma, necessitating adjustments for the unique composition of milk.

Purpose of the Study:

• To determine the concentration of ionized calcium (Ca2+) in human milk.
• To establish a reliable method for measuring Ca2+ in human milk, accounting for its distinct properties compared to plasma.

Main Methods:

• Utilized a Radiometer ionized calcium analyzer calibrated for the specific pH and ionic strength of human milk.
• Employed glass capillaries to minimize carbon dioxide (CO2) loss from samples during measurement.
• Verified that no other milk constituents interfered with the calcium ion-selective electrode response.

Main Results:

• The ionized calcium (Ca2+) concentration in human milk samples was measured at 2.84 (SD 0.56) mmol/L at pH 6.98.
• Observed that loss of CO2 from milk samples led to decreased Ca2+ concentration and increased pH.
• Demonstrated the critical role of maintaining physiological CO2 levels for accurate Ca2+ determination.

Conclusions:

• The study highlights the importance of controlling for CO2 levels and adjusting for pH when measuring ionized calcium (Ca2+) in human milk.
• The developed calibration method provides a more accurate assessment of Ca2+ in human milk.
• Maintaining physiological CO2 concentrations is vital for reliable Ca2+ analysis in milk samples.