The Shindingen Isfet pH meter is a simple unit, measuring just 142 x 28 x 15 mm and powered by two 3V lithium batteries. Designed for both laboratory and field work, the meter is supplied in a hard carrying case with room for two small bottles of calibration buffers (pH 6.9 and 4.0). The unit is shaped like a pen, with the electrode at one end, and an LCD display and rubber control buttons at the opposite end. Specific error messages are displayed for calibration errors or when batteries need to be replaced. The semiconductor electrode can also be replaced, a simple and not too expensive exercise. The meter functions in the pH range 2.0 – 12.0, with the digital display showing the pH to one decimal place. The meter functions in the temperature range of 5 – 40ºC, and has an automatic temperature compensation. An automatic power-off function helps to prolong battery life and a cap prevents the electrode from drying out.
As expected from a basic unit, operation is straightforward and the calibration routine is easy to commit to memory. To use the 2–point calibration system, the electrode is washed with water and wiped clean. The first buffer (pH 6.9) is applied to the electrode, and the CAL1 button depressed. A flashing sign indicates the calibration process is underway. The electrode in then cleaned again, the second buffer (pH 4.0) applied and the CAL2 button depressed. The whole process requires no more than 1-2 minutes. Samples are measured in the same way, with a careful wash and wipe of the electrode between each one.
Large volumes can be measured with the meter either placed or held in the sample so that the electrode is covered. As the electronics are located at the opposite end to the electrode, chances of water damage are minimized. When measuring large volumes, it is recommended that the pH meter is placed in a stand to prevent accidental immersion. A particularly useful feature is the ability to measure just a few drops of a sample when the unit is placed horizontally on the bench. This function allows small volumes of precious or sterile liquids to be tested. Unfortunately, the shape of the pH meter means small volumes in standard 10, 15 or 50 ml plastic tubes cannot be measured.
I have used this Shindingen pH meter for general laboratory use for the past 5 years, and have found it extremely reliable. Battery and electrode replacements have been minimal, and the padded hard case has protected the pH meter from both spills and knocks.
Research Scholar
School of Molecular and Microbial Sciences
The University of Queensland