Benchtop Basics: Tips for Buying pH Meters and Balances

Featured Article

110504-187x140.jpg

Please check out our Laboratory Balances, Portable pH Meter / Hand Held pH Meter and Benchtop pH Meter sections for more information or to find manufacturers that sell these products.

Most laboratories would grind to a halt without the fundamental measurements provided by instruments for electrochemistry and weighing instruments. Basic equipment like pH meters and conductivity meters are based on, or are closely related to, the heart of electrochemistry—when charged particles, such as ions or electrons, traverse an interface between two phases of matter. This interface is usually a metal (such as an electrode) and a conductive solution or electrolyte. Researchers now have many options among which to choose electrochemistry equipment. This article aims to help introduce the types of electrochemistry tools available today. (See box for tips on choosing an analytical balance.)

pH meters

A pH meter is an irreplaceable piece of equipment for measuring the acidity or alkalinity of a solution (or a semisolid). Usually a measuring electrode and a reference electrode are connected by a meter for comparison. The hydrogen ion-sensitive measuring electrode measures a small voltage that changes depending on the concentration of hydrogen ions in solution. The pH meter then displays the measurement in pH units (and in some cases, also in mV or conductivity). Because the pH reading is sensitive to temperature, some pH meters offer a temperature compensation feature (automatic or manual) that can correct this potential source of variation.

Benchtop pH meter options

Another variable feature of pH meters is the measurement range. For example, the SevenEasy™ S20 pH Meter from Mettler-Toledo (Columbus, OH) has a pH range of 0.00–14.00. The HI 4521 pH/Conductivity (USP) Bench Meter from Hanna Instruments (Smithfield, RI) has a pH range from –2.000 to 20.000 pH (as do other Mettler-Toledo models). Many models of benchtop pH meters are available, including those offered by Hanna Instruments, Mettler-Toledo, Denville Scientific (Metuchen, NJ), Sartorius Group (Goettingen, Germany), and OMEGA Engineering (Stamford, CT).

Handheld pH meter range

While many researchers use a benchtop pH meter, others can benefit from a handheld or portable model. Since some may use them outdoors, portable models also come in sturdy, weather-resistant designs, such as the HI 9026 Rugged Waterproof pH Meter from Hanna Instruments. Other vendors of portable pH meters include Mettler-Toledo, Sartorius Group, and OMEGA Engineering. As with any portable electronic laboratory instrument, it is a good idea to know in advance how long the battery will last (especially if out in the field), and the method of data transfer from the instrument to the laboratory computer.

Conductivity meters

Like pH meters, conductivity meters serve a fundamental purpose in many laboratories. The main function of conductivity meters is to measure the electrical conductivity of aqueous solutions (in units of mS/cm), but they can also measure other quantities, such as the amount of total dissolved solid (TDS), the pH, the percentage of sodium chloride in solution, resistance, and temperature. Conductivity is also temperature-dependent; thus most meters offer some type of temperature compensation, whether automatic or manual. Besides giving various types of readouts, conductivity meters also vary in their ranges of measured conductivity. For example, the EC 215R Multi-range Conductivity Meter with Automatic Temperature Compensation and Analog Output (Hanna Instruments) has a range of 0.0–199.9 mS/cm, while theSevenMulti S70 Luxury Conductivity Meter (Mettler-Toledo) has a range of 0.001–1000 mS/cm.

Benchtop conductivity meter and portable conductivity meter choices

Benchtop conductivity meters can be obtained from many vendors, including some who also make pH meters, such as Hanna Instruments, Mettler-Toledo, Sartorius Group, OMEGA Engineering, Metrohm USA (Riverview, FL), and Taylor Scientific (St. Louis, MO). Similar to pH meters, conductivity meters also come in portable or handheld models and include all the extra features of their benchtop cousins. They also feature a range of measurement capabilities: Portable Conductivity Meters from Sartorius measure 0.0–199.0 mS/cm, and the HI 98188 Waterproof Portable EC/Resistivity/TDS/NaCl and Temperature Meter from Hanna Instruments measures 0–1000 mS/cm. As mentioned above, for portable pH meters, it is important for the user to learn about expected battery lifetimes, and the means of data transfer from the conductivity meter to the lab computer. Portable units can be found from Hanna Instruments, Mettler-Toledo, Sartorius Group, OMEGA Engineering, and PID Analyzers (Pembroke, MA), among others.

Comments