pH Meters

pH – MORE THAN AT A GLANCE

pH is a measure of the alkalinity or acidity of a nutrient solution. A neutral solution is numerically equal pH 7; as the solution gets more acidic, the numbers decrease and increase as it becomes more alkaline or basic. Pure water is neither alkaline nor acidic, rather it is neutral.

This sounds quite simple until we begin to evaluate which meter we should use because this evaluation requires close scrutiny not only of the product we choose, but also we must make our selection of the meter select based on:

ACCURACY – typically from pH +/-0.1 to pH+/-0.01

ATC – AUTOMATIC TEMPERATURE COMPENSATION – When there is an increase or decrease in the temperature of a solution, the pH of the solution can change. With ATC, the meter signals the sensor and corrects the pH reading for changes in the electrodes sensitivity at that temperature. (Oakton pH meters – www.southernlabware.com)

CALIBRATION – Your pH meter is calibrated using buffers of a known pH by immersing the electrode and adjusting the meter accordingly. The electrode should always be rinsed with distilled water after each calibration point is established. For example, in some cases a 5-point calibration may be recommended. (pH Buffers –

ELECTRODE – A solution is like a battery and can generate an amount of voltage depending on the concentration of Hydrogen (H+) ion present. pH electrodes measure the voltage or potential difference of the solution in which it is dipped. Glass electrodes are the most popular and successful electrochemical sensors. It consists of a glass bulb membrane, hence its name, and a tubular body which separates an internal solution and a silver/silver chloride electrode from the tested solution. This is hooked up to a pH meter which is in reality a voltmeter which measures the potential difference and its changes across the glass membrane. There are single junction and double junction electrodes as well as stainless steel, single junction and double junction electrodes that may be replaceable or non-replaceable. (Electrodes available at Buy Electrodes from ph meters and testers ).   

RESOLUTION – This term should not be confused with ACCURACY. The resolution is the smallest value that is shown on the instruments display. Thus an instrument that has a 0.01 pH means that it will read to the nearest 0.01 pH; for example 8.06 pH. The better the resolution, the better is the measurement display capability of the meter. This may not mean that this is a more accurate pH meter, however it does usually indicate a superior instrument. (Waterproof, double-junction pH Testr 30 by Oakton at (Buy Electrodes and Waterproof, double-junction pH Testr 30 by oakton at ph meters and testers).

When choosing which pH meter is best for your application, price may be a factor and a meter that costs twice what another one costs does not always mean it will deliver results that are twice as good. Always compare specifications to get the best value and, important too, compare the replacement costs of the electrodes or other probes for your meter. Remember, first determine your application needs, then compare these factors: ACCURACY, ATC, CALIBRATION, ELECTRODES, RESOLUTION.