The pH meter is an essential piece of equipment in most laboratories, vital for many analytical and synthetic processes. Typical pH meters consist of a glass electrode connected to an electronic meter. The electrode produces a small voltage, which is converted to and displayed in pH units by the meter.
pH meters are used in many industries: chemical, biological, environmental, forensics, consumer products, foods, and many others for which acidity measurements are required. A significant application is monitoring titration, a lab method that quantifies the concentration of an analyte in solution. Acid-base titrations measure concentrations of an acidic or alkaline substance. From the quantity of neutralizing species (acid or base) – added at the point where pH is 7, or neutral – one can calculate the original concentration of the acid or base in the solution.
Like many laboratory instruments, pH meters have evolved beyond all recognition over the last several decades. However, experts predict a gradual evolution rather than a revolution in the design of pH meters during the coming years. It seems likely that the product hardware will continue its trend towards miniaturization, while software will undoubtedly become easier to develop and use. Although its form and function may change little in the immediate future, it seems certain that the pH meter will continue to enjoy its status as one of the most ubiquitous pieces of laboratory equipment.
Close to 90 percent of the respondents have either a benchtop or portable handheld pH meter. Benchtop pH meters offer the greatest versatility and, depending on which one you choose, there are flexible models that can provide the option to add built-in printers, data loggers, many different probe arms, and accessories. Portable handheld pH meters in the past lacked some of the sophisticated features of their benchtop counterparts, but many of the portable models on the market today are nearly as advanced. The new generation of portable meters can be a very attractive, if not required, option for lab or field use.
Type of pH meter respondents are using or planning to purchase.
|Benchtop pH meter||58%|
|Handheld pH meter||29%|
|Tester pH meter||6%|
|In-line pH meter||6%|
A team at Oxford University in the UK patented a revolutionary type of pH meter – the solid state sensor pH meter. This pH meter replaces sensitive glass electrodes with a solid-state sensor that is insensitive to temperature changes and may be sterilized. According to respondents who purchased this pH meter, the device provides robustness and miniaturization and never requires calibration.
Twenty four percent of the respondents have or are planning to purchase a solid state sensor pH meter.
|No, but planning to purchase||13%|
|No, and no plans to purchase||76%|
The methods for measuring pH fall roughly into the following categories: glass-electrode methods; indicator methods; metalelectrode methods (including the hydrogen-electrode method, quinhydron-electrode method, and antimony-electrode method).
Over 50 percent of the respondents use the glass-electrode method. In this method, the known pH of a reference solution is determined by using two electrodes, a glass electrode and a reference electrode, and measuring the voltage (difference in potential) generated between the two electrodes. The difference in pH between solutions inside and outside the thin glass membrane creates electromotive force in proportion to this difference in pH. This thin membrane is called the electrode membrane.
Measuring pH using an indicator includes two methods: one involves comparing the standard color corresponding to a known pH with the color of an indicator immersed in the test liquid using buffer solution; the other method involves preparing pH test paper that is soaked in the indicator, then immersing the paper in the test liquid and comparing its color with the standard color. This method is simple, but prone to error. A high degree of accuracy cannot be expected.
Metal-electrode methods – A hydrogen electrode is made by adding platinum black to platinum wire or a platinum plate. It is immersed in the test solution and an electric charge is applied to the solution and platinum black with hydrogen gas. The hydrogen-electrode method is a standard among the various methods for measuring pH. However, this method is not appropriate for daily use because of the effort and expense involved, with the inconvenience of handling hydrogen gas and the great influence of highly oxidizing or reducing substances in the test solution.
Over the years, lab workers have come to expect more from instrumentation and pH meters are no exception. There are many different features of a laboratory pH meter to take into account before making your purchase, including accuracy, calibration type and number of calibration points, intuitive operation, expandability, reliability, and value. There are three main selection criteria respondents recommend purchasers to consider before buying a pH meter: look at where you will be using your pH meter – in the field, around your lab, or sitting on your benchtop; pH detection range; and pH resolution. Other factors to take into consideration in purchasing a pH meter are the instrument’s resolution and accuracy, probe type (detachable or integrated), electrode type (sealed or longer-lived refillable), auto-calibration with temperature compensation, automated uploading, and operational modes for specific industries or situations. Users are also looking for broader functionality, such as conductivity and ion selectivity in one instrument.
The number one feature is ease of use with auto calibration a close second. Respondents recommend that purchasers take a hard look at ease of calibration, because there’s a wide spectrum of technical astuteness among users. Some methods, particularly in regulated industries or engineering, may call for a three-, four-, or five-point calibration; others are conducted in extreme environments. Hence, end users are looking for a pH meter they can calibrate easily within their application’s operating range.
Top 10 factors/features that influence the buying process.
|Ease of use||95%|
|Auto calibration with temperature compensation||93%|
|Low maintenance/easy to clean||92%|
|Resolution and accuracy of the meter||89%|
|Availability of supplies and accessories||82%|
|Detachable electrode probe||79%|
|Service and support||71%|
|Longer-lived refillable electrode type||70%|
|Multi-level LCD display; display the current measurement simultaneously with the current temperature.||68%|
|Heavy-duty and waterproof||54%|
Completed Surveys: 354
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