With so many options in Thermo Scientific’s Orion Star A line, it can be difficult to narrow down which meter will best fulfill a project’s needs. One easy way to rule out some meters is by considering application type. For projects that rely largely on collecting samples in the field, a portable meter is clearly the way to go. But there’s still a handful of meters to choose from.
To simplify making the right choice, we spoke with Ricki Hartwell, the global product manager for Thermo Scientific’s Orion Laboratory and Field Instruments. She recently shared her tips on choosing the right Thermo benchtop. Let’s take a look at her recommendations for selecting the right portable meter.
“For our portable Star A meter line, we have premium (Star A320 series), advanced (Star A220 series) and basic (Star A120 series) meters that offer customers the best match based on their required features, performance specifications and budget,” said Hartwell. “Our entire series of Star A portable meters are IP67, waterproof-rated for durable field measurements.”
The Star A120 series basic portable meters are economical field meters offering simplified, easy-to-read displays and user-friendly operation. They have basic, on-screen text prompts, emphasized measure keys and reading stability indicators that remove common complications from taking measurements.
“Orion Star A120 series portable meters are ideal for the academic / educational and municipal water utility markets because they are a great value with simpler operation,” said Hartwell.
The A120 series includes the A121 portable pH meter, the A122 portable conductivity meter and the A123 portable dissolved oxygen meter. All of the meters allow for immediate onsite spot measurements. This helps remove some of the errors involved with transporting samples back to the lab, which is especially important when taking dissolved oxygen measurements, says Hartwell.
Each A120 series meter can operate continuously for more than 2,000 hours on four AA batteries and all offer manual and automatic and calibration options. These are helped by an AUTO-READ function on each A120 meter that tells users when calibration readings are stable. Up to 50 GLP-compliant data points can be stored on each A120 and they all come with a 3-year warranty. Transferring data to a computer or printer is possible through USB or RS232 ports.
The Star A220 series advanced portable meters are easy to use, dependable, single-parameter meters for dedicated measurement needs. Like the A120 basic series, they offer an easy-to-read graphic display with backlight and intuitive operation. This is made possible by instructions that are presented on the screen and a keypad that includes menu-specific function and shortcut keys for quick meter navigation and control.
The A220 series includes the A221 portable pH meter, A222 portable conductivity meter, and the A223 portable RDO/DO meter. They offer slightly more robust performance when collecting data in a field setting, largely because of a few improvements. The A220 series meters have on-screen reading stability indicators like Thermo’s basic portables, but their memory is considerably enhanced, featuring a 1,000-point capacity for GLP-compliant readings.
Transferring data to a computer or printer is possible through each meter’s USB or RS232 ports. And Hartwell says that measurements can be obtained using both AUTO-READ and continuous read modes. Each A220 meter features a 3-year warranty and can operate continuously for more than 800 hours on four AA batteries.
Thermo’s A320 advanced series meters are the ones Hartwell most recommends for spot sampling applications. This is because they are the best performers all around. Still, their battery life isn’t as good as the A120 series (800 hours on 4 AA batteries) but the trade-off is worth it, she says.
The A320 series includes the A321 portable pH meter, A322 portable conductivity meter, A323 portable RDO/DO meter, A324 portable pH/ISE meter, A325 portable pH/conductivity meter, A326 portable pH/RDO/DO meter and the A329 portable pH/ISE/conductivity/RDO/DO meter.
She broke down her meter choices for some of the most common parameters that customers measure in the field, including dissolved oxygen, pH and conductivity.
For DO, she recommends the Orion Star A323 RDO/DO portable meter. It measures dissolved oxygen in percent saturation or milligrams per liter with temperature, using either Orion polarographic or RDO optical DO sensors with automatic sensor recognition and utilizes a built-in barometer that automatically adjusts DO readings for barometric pressure.
The A321 portable pH meter, she says, is most ideal for taking field measurements of pH, millivolts, relative millivolts or ORP with temperature measurements, she says.
“The meter can perform up to a five-point pH calibration with easy-to-follow onscreen instructions (and) automatic buffer recognition,” said Hartwell. It is possible to enter custom buffer values, as well, plus there’s an option for editing a calibration so that individual points can be fixed without the need to complete a new calibration.
For taking conductivity measurements, Hartwell says that the A322 portable conductivity meter has a lot of versatility, which is why it’s her top choice for spot sampling. It can measure conductivity, total dissolved solids, salinity or resistivity with temperature and also can perform up to a five-point calibration.
Other A320 meters are ideal if only a few things need to be tracked, says Hartwell.
“Select the Star A325 pH/conductivity portable meter, Star A326 pH/RDO/DO portable meter or Star A329 pH/ISE/Conductivity/RDO/DO portable meter to measure two to four main parameters with temperature simultaneously,” said Hartwell.
Data transfer is completed with the A320 series meters just like with other Thermo portables, and they feature 3-year warranties as well. But the A320 advanced meters offer a sizable memory advantage when compared to the others, with capacity for storing up to 5,000 GLP-compliant data points.
Durable electrodes are important for reliable field sampling, which is why most of those available with the Orion Star A portable meters have epoxy bodies that hold up well against corrosion and provide steady performance over time. Hartwell says that temperature compensation is another key factor in field applications and all of the meters incorporate that in some way. Since it’s not practical to fumble with refilling electrode reference solution on the go, picking electrodes that are gel-filled is more ideal.
For pH measurements, one electrode works with all Star A portable meters – the Orion ROSS Ultra pH/ATC Triode. Hartwell says that ROSS electrodes have a reversible reference system that’s quick to balance and remains soluble over a broad range of temperatures. The ROSS Ultra pH/ATC Triode has an epoxy body, a waterproof BNC connector and is filled with a low-maintenance gel.
“It has a very stable millivolt signal across a range of temperatures, so the reference potential does not shift significantly with temperature changes,” said Hartwell. “This reversible reference system can extend the useful life of ROSS pH electrodes, especially when the electrode is used at high temperatures.”
Conductivity measurements across the line are accomplished using Orion DuraProbe 4-electrode conductivity cells. These are available with different cable lengths and come with Mini-DIN connectors.
Lastly, most of the available attachments to measure dissolved oxygen with the Star A portable meters are Orion RDO optical DO sensors. These work through a low-maintenance and easy-to-change optical cap that is protected by a stainless steel guard. For readings at a short notice, these are the way to go. But there is also the Orion Polarographic Dissolved Oxygen Probe, which is a little less costly. It features temperature compensation, and membranes that aren’t difficult to change, but does require a short warm-up time before it’s ready to sense DO levels.
For customers measuring less-common parameters such as ammonia, fluoride or sodium, ion-selective electrodes are available. A ROSS sure-flow combination electrode is available for sodium measurements, which helps ensure movement of solution within it. The other ISEs, for ammonia and fluoride, are simple combination electrodes but don’t feature sure-flow technology.