Thursday, April 26, 2012
Featured Article
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.)
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.
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).
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 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.
Few laboratories could function without the basic benchtop analytical balance for weighing chemical compounds, or any small lab item. Researchers can find balances with different ranges of measurements; therefore it is a good idea to consider not only what needs to be weighed now, but also potential future uses. Most models can read from 0.01 or 0.1 mg up to tens or hundreds of grams. The cost and accuracy of a balance are strongly influenced by the quality of its weighing sensor, which is inside the instrument and translates the item’s weight into a number. The better the weighing sensor, the faster and more reproducible the balance will be. It will also provide better protection from thermal fluctuations in measurements.
Because balances come in several varieties, it is beneficial for the user to envision potential applications before purchase. The ubiquitous benchtop analytical balance features different calibration options: manual or automatic (and, in some cases, programmable) and external or motor-driven. If a balance will be situated in a particularly dusty environment, the user should consider one that has been rated for ingress protection (IP); higher IP ratings indicate better resistance to solid and liquid contamination. Other enclosures need to be considered if biohazardous materials will be used.
It is also important to consider the weighing range that will be most needed, since models differ. For example, Precision Analytical Balances from Denville Scientific feature a capacity of 120–250 g, and Excellence Plus XP Analytical Balances from Mettler-Toledo have capacities of 120, 220, or 520 g. Many companies offer analytical balances, including Sartorius Group, Denville Scientific, Mettler-Toledo, Taylor Scientific, MIDSCI (St. Louis, MO), OHAUS (Parsippany, NJ), Scientech (Boulder, CO), Shimadzu (Columbia, MD), Tovatech (South Orange, NJ), A&D Weighing (San Jose, CA), Adam Equipment (Danbury, CT), BioMedical Solutions (Stafford, TX), Rice Lake Weighing Systems (Rice Lake, WI), and Spectrum Chemical (New Brunswick, NJ).
Researchers working in the field (or lab members whose experiments demand extra mobility) may prefer a portable analytical balance. Compared to other balances, a unique feature of portable units is their ruggedness for travel. They can offer many of the same features (perhaps sacrificing some degree of precision) as benchtop models, but with more durability. Portable balance vendors include Denville Scientific, Mettler-Toledo, OHAUS, Shimadzu, Adam Equipment, Rice Lake Weighing Systems, Spectrum Chemical, and Terra Universal (Fullerton, CA).
Those who do not need the higher accuracy and protection afforded by an analytical balance may choose a top-loading balance. Generally used for weighing larger amounts (i.e., with a 0.05-g margin of error), a top-loading balance is easy to use. However, top-loading balances provide no protection from drafts, dust, or other environmental contaminants. They do vary in their weighing capacities, though, and because of this researchers need to know what they will be used for. For example, the OHAUS Explorer Pro Precision Balance has a capacity of 210–32,000 g, while the Denville Scientific Precision Top Loading Laboratory Balance has a capacity of 150–4500 g. Top-loading balances are available from many companies, including Denville Scientific, Mettler-Toledo, MIDSCI, OHAUS, Sartorius Group, Scientech, Shimadzu, Terra Universal, Tovatech, A&D Weighing, Adam Equipment, Rice Lake Weighing Systems, Spectrum Chemical, and Taylor Scientific.
Conclusion
Electrochemistry equipment such as pH meters, conductivity meters, and balances provide essential, everyday measurements that researchers could not function without. Hopefully the considerations discussed here will help users find the right instrument to fit their needs. For other manufacturers and distributors, please visit www.labcompare.com
Caitlin Smith is a freelance science writer who has a Ph.D. in Neuroscience from Yale University and postdoctoral work in Electrophysiology and Synaptic Plasticity; e-mail: caitlin.smith@comcast.net .
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.
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