Abstract: A method and device to predict ovulation in a female human by measuring changes in the concentration of a number of ions in eccrine sweat is disclosed. The concentration, or changes in concentration, of one or more ions are determined throughout the day and analyzed against predetermined patterns in order to predict ovulation one to five days in advance. This permits the user to more accurately determine commencement of the fertile phase, which for female humans is generally considered to be about four days prior to ovulation to one day after ovulation. The concentration of the ions measured include sodium (Na+), potassium (K+), ammonium (NH4+), calcium (Ca2+), chloride (Cl?) and nitrate (NO3?). To further increase the accuracy of the reading, a large number of readings can be obtained throughout a day and statistically analyzed to determine the change over time. In addition, the concentration of two or more ions can be obtained to increase accuracy.

Abstract: Reference electrodes for potentiometric measurement of pH and ion concentration typically use mercury calomel or silver/silver chloride element combined with a saturated solution of potassium chloride (KCl) for the development of a stable potential with respect to a sensing electrode when immersed in solution. The salt KCl is preferred because of it is almost equitransferent and thus minimizes the diffusion potential set up between the reference solution and the solution being tested. However, reference electrodes using concentrated solutions of KCl suffer a drawback, which is its propensity to develop a creeping salt discharge that rapidly covers surfaces with KCl crystals. This “salt creep” phenomenon appears to be unique to KCl; Salt creep is a major nuisance, particularly for reference electrodes used on semi-dry surfaces such as skin.