Laboratory pH Electrode Selection Guide

Introduction

pH is one of the most fundamental parameters measured in nearly every application. Different electrode requirements exist for different applications. Due to these various requirements, YSI offers a suite of laboratory combination pH electrodes to ensure selection of an electrode that meets application demands. This guide provides a description of each component of a pH electrode, an overview of each YSI lab electrode family, and specifications for each YSI electrode. For additional assistance in selecting a pH electrode, consult the YSI Laboratory pH Electrode Application Guide, and for practical guidance regarding pH measurement, refer to the YSI pH Handbook.

pH Electrode Design

Choosing the right electrode for your needs begins with an understanding of the different structures that make up a pH electrode.

Temperature sensor (optional)

Some electrodes feature an integrated temperature sensor. pH values are dependent on temperature, so pH measurements should always be completed with an accurate temperature sensor.

Reference electrolyte

The electrolyte has connection to the sample through the junction. Potassium chloride (KCl) is the most common electrolyte used and can be in the form of liquid or gel. Liquid electrolyte provides faster measurement results and decreases the possibility of measurement errors due to diffusion potentials.

Electrode body

Plastic body electrodes are more rugged, less likely to crack, and commonly feature gel electrolyte. Glass body electrodes have a wider range of operating temperatures and many are refillable.

Glass membrane

Specialized glass that is sensitive to hydrogen ion activity. Filled with buffer of known pH, creating an environment of constant binding of hydrogen ions on the inside while the sample outside has a variable amount of hydrogen ions. This difference in hydrogen ions creates an electrical potential. The shape of the membrane can vary in order to ensure optimal moistening. Unique applications may require a specialized membrane shape.

Refill opening (optional)

Since electrolyte escapes through the reference junction, electrodes that can be refilled with liquid electrolyte tend to have a longer life than non-refillable electrodes.

Reference electrode

Designed to maintain a constant electrical potential. The difference in electrical potential between the reference and sensing electrode results in a voltage that is used to calculate a pH value. The silver/silver chloride reference system is the most common, although the iodine/iodide system has many advantages.

Reference junction

Allows for electrical contact between the reference electrode and the solution. Slightly permeable to prevent electrolyte from escaping too quickly. Different junctions are available, each with unique characteristics.

YSI pH Electrode Families

YSI has three different families of combination pH electrodes from which to choose, each with unique characteristics. The IDS electrodes are designed for use with the YSI MultiLab, a multiparameter digital lab instrument. TruLine and Science electrodes feature BNC connection and are designed for use with the YSI TruLab, although they can be connected to the MultiLab via a BNC adapter.

MultiLab IDS

• Intelligent digital sensors (IDS) for the YSI MultiLab
• Store calibration status and serial number, even if disconnected from the meter
• Double-junction with Ag/AgCl reference system
• All electrodes have an integrated temperature sensor
• Available in gel-filled or liquid electrolyte versions; glass or plastic body

Science

• Designed for use in unique applications that require a particular junction
• Features the Silamid reference system, a unique construction of the Ag/AgCl reference system resulting in a more stable and longer lasting electrode with a fast response
• Double-junction reference and integrated temperature sensor
• Ground-joint junction with a fast electrolyte outflow is specifically designed for samples high in solids or with low ionic strength
• Platinum junction for applications that do not require a rate of electrolyte outflow as fast as the ground-joint
• BNC connector; compatible with any pH meter that has a BNC input

TruLine

• Designed for use in typical laboratory applications
• Single-junction electrodes with Ag/AgCl reference system
• Integrated temperature sensor option
• Durable electrodes with gel electrolyte for general use; liquid electrolyte sensors for more critical measurements
• Electrodes with special membranes for unique applications
• BNC connector; compatible with any pH meter that has a BNC input

YSI pH Electrode Comparison

The following comparison is designed to assist in selecting the electrode that best fits your needs. For additional information, the manual for each electrode can be found on YSI.com.

Electrode Characteristics

Membrane Shape Properties

Detailed Electrode Specifications

* Minimum immersion depth is the distance from the tip of the membrane to the outer junction. The junction must always be completely immersed when taking a measurement.

Calibration Buffers and Solutions

YSI calibration buffers are available in pH values of 4, 7, and 10. The following are available:

• 003821: pH 4 Buffer (box of 6 pints)
• 003822: pH 7 Buffer (box of 6 pints)
• 003822: pH 10 Buffer (box of 6 pints)
• 603824: Assorted Case (2 pints each of pH 4, 7, and 10 buffers)

Potassium chloride (3 M KCl) solution is available (109 705Y) for refillable electrodes. 3 M KCl is also the recommended storage solution for all YSI lab pH electrodes.

Temperature Sensors

External temperature sensors are available for electrodes that do not have an integrated temperature sensor. Examples include ScienceLine Temp 135 and ScienceLine Temp 136 Sensors.

YSI Instruments

YSI MultiLab

IDS (Intelligent Digital Sensor) pH electrodes feature a digital connector and are designed for use with the YSI MultiLab, a multiparameter digital instrument. A BNC adapter (108132Y) also allows these electrodes to be connected to the MultiLab 4010-2W and 4010-3W.

YSI TruLab

The TruLine and Science pH electrodes feature BNC connection and are compatible with any pH meter that has a BNC input, such as YSI TruLab meters. The YSI TruLab can also make use of analogue ISE (Ion Selective Electrode) probes with a BNC connector.

*There is an integrated printer option for the MultiLab 4010-1, TruLab 1310, and TruLab 1320.