The Measurement of pH is one of the most common analytical techiques used in chemistry to measure a solutions degree of acidity or alkalinity. pH is measured on a scale of 0 to 14. The term "pH" is derived from "p", the mathematical symbol of the negative logarithm, and "H", the chemical sysmbol of Hydrogen. The formal definition of pH is the negative logarithm of the Hydrogen ion activity expressed as;

pH = -log[H⁺]

pH provides the needed quantitative information by expressing the degree of the activity of an acid or a base in terms of the hydrogen ion activity. The pH value of water is directly related to the ratio of the hydrogen ion [H⁺] and the hydroxyl ion [OH^-] concentrations. If the H⁺ concentration is greater than the OH^-, the water is acidic ( the pH value is < 7.0). If the H⁺ concentration is less than the OH^-, the water is basic ( the pH value is > 7.0). If the H⁺ concentration is equal to the the OH^-, the water is nuetral ( the pH value = 7.0)

A rough indication of pH can be obtained using pH papers or indicators, which change color as the pH level varies. These indicators have limitations on their accuracy, and can be difficult to interpret correctly in murky samples. More accurate pH measurements are obtained with a pH meter. The AAS pH Measurement System consist of three parts: (1) a pH measuring electrode with a reference electrode, (2) a pH Pre-amplifier, and (3) a high input impedance mVDC 7018 Input Module. The pH electrode can be thought of as a battery, with a voltage that varies with the pH of the measured solution. The pH electrode is a hydrogen ion sensitive glass bulb, with a millivolt output that varies with the changes in the relative hydrogen ion concentration inside and outside of the bulb itself. The reference electrode ouput does not vary with the activity of the hydrogen ion. The pH Pre-amplifier has a high input impedance that can accurately measure the minute electrode voltages and with its low output impedance drive the mV DC Input within the DP7000 Distribution Panel where the values are converted and then transfered over the RS485 serial I/O bus to the PC and displayed using the AMACS Software.