YVCC teaching Winery Instructional Series
Measuring pH using the SevenGo pH Meter

Gather the following equipment: pH Meter; small plastic beakers (100mls), pH Buffer Solutions; a 1 L DI water bottle; one -- 250 mL waste container or beaker and a supply of Kimi wipes.

The pH meter is used to measure the acidity or alkalinity of a liquid through a probe by reading the reactivity of hydrogen ions.

The SevenGo SG2 pH meter allows you to perform 1, 2 and 3 point calibrations.

To calibrate the meter, obtain two or three pH buffer standards. When performing a two buffer calibration it should be buffer solutions of pH 4 and pH 7.
A three buffer calibration will also use ten. Any solutions dispensed into another container should be clearly marked and dated for the date dispensed.

To perform a 2 point calibration:

Power on the meter.

Rinse the electrode with deionized water and blot dry with a kimi wipe

Place the electrode in a calibration buffer solution and press the "Cal" button. After the reading has stabilized it will show a percentage value of the slope.

Rinse the electrode in deionized water.

Place the electrode in the next calibration buffer solution and press the "Cal" button.

The SG2 self calibrates after the signal from the probe has stabilized or after pressing the "Read" button. The meter displays and freezes the relevant buffer value, and updates the calibration adjustment on the display.

To accept the calibration and return to sample measurement, press the "Read" button.

To perform a 3 point calibration, perform the same steps as the 2 point calibration and repeat steps 3 and 4 for the third calibration point.

This electrode contains a temperature sensor and auto corrects for temperature variation. However, calibration buffers and liquid samples should fall between 20 and 25 degrees C for the most accurate results.

Rinse the electrode with DI water prior to placing it into the sample.

Place the electrode in the sample and press "Read" to start the measurement: the decimal point blinks.

The display will begin to show the pH of the sample. The automatic end point "A" is the default setting of the meter. When the signal has stabilized, the display freezes and ?? appears over the "A".

The stability criterion for pH and mV measurements will appear when the signal inputs have not changed by more than 0.1 mV in a 5 second period.

Continue to "Read" the sample after stabilization until the pH no longer varies by more than a value of +/- 0.01

The SevenGo meters do not require any maintenance other than a wipe with a damp cloth and occasional battery replacement. The two halves of the unit should never be disassembled.

Electrode Maintenance:

Always make sure the electrode is stored in an appropriate storage solution. Never allow the electrode to dry out. For maximum accuracy, any filling solution that has encrusted the outside of the electrode should be removed with DI water.

If the electrode slope falls rapidly, or if the response is sluggish, the following procedures may help.

If the sensor membrane has dried out, soak the tip of the electrode overnight in a 0.1 HCl solution.

If a protein build-up has occurred in the diaphragm, remove deposits by soaking the electrode in an HCl/pepsin solution (#51340068). 5e end

After treatment a new calibration should be performed.

The Sevengo pH meter continuously measure electrode condition. A bar indicator on the upper right of the meter display screen shows the current electrode condition. When the graphic displays three bars the unit is on good condition. At two bars the electrode is in need of cleaning. One bar indicates the electrode is faulty and in need of replacement.

Note: Cleaning and filling solutions should be handled with the same care as that given to toxic or corrosive substances.

pH buffer solutions that have been dispensed into containers for calibration should be dated when dispensed.

Dispensed pH buffer solutions should be replaced weekly with fresh solution.

Expired pH buffer solution should be neutralized prior to disposal.

A pH of seven is considered neutral.