In this blog post I continue to discuss the selection criteria for discrete analyzers. To learn what a discreet analyzer is and how it works, read my previous blog post.
Discrete analyzers consist of four components: a photometer with a specific number of filter positions, dispensing probes, an incubator to control the reaction temperature, and a mixer. In discrete analysis, each individual reaction cell is isolated and the temperature is stabilized, enabling highly controlled reaction conditions.
Photometric setup in a discrete analyzer
Every discrete analyzer has a photometric measurement setup with finite numbers of filters of specific wavelengths. The number of filters and wavelength of filters are important technical features to evaluate during the purchase phase as it can directly affect the lab’s current and future application capability.
The number and the type of chemical parameters that a discrete analyzer can perform simultaneously are directly dependent on the number of filters and their wavelengths. Discrete analyzers typically have five to 12 filters — equivalent to channels in flow analyzers — and are suitable for multiparameter analysis. Many of the entry level discrete analyzers have five to six onboard filters with limited wavelength coverage. Advanced discrete analyzers like the Thermo Scientific Gallery and the Gallery Plus Discrete Analyzers have 12 filter positions. And, depending on the configuration, have nine to 11 onboard filters. The high number of onboard filters allows the Gallery discrete analyzers to perform up to 20 different chemistries simultaneously, depending on the applications.
Discrete analyzer – source lamp type and lifespan
A source lamp is an important part of the discrete analyzer’s photometric hardware setup. Spectrophotometer design, more specifically the type of lamp and internal optical configuration used, contributes to varying performance characteristics that can influence the efficiency of a discrete analyzer. The source lamp ideally should cover a wide wavelength range, long service life, and low cost. Most of the discrete analyzers are equipped with tungsten lamps as the source lamp and can cover only the visible range. Any measurement below 340 nm is not possible with a discrete analyzer that uses tungsten as the source lamp. To cover the ultraviolet (UV) range, a deuterium lamp is needed and is not used in discrete analyzers, meaning an application like bitterness in beer, which is done at 275 nm, is not possible with this type of discrete analyzer.
Discrete analyzers that use tungsten source lamps are considerably less efficient, as they cover only the visible range. Furthermore, they must continue to operate during the entire instrument up-time. This contributes to shorter lifetimes and higher instrument maintenance costs. Depending on the usage, the tungsten source lamp requires replacement every six months, which can cost hundreds of dollars. Over the instrument’s lifetime, which is typically 10 years, cumulative replacement expenses can be very high, assuming they are user-replaceable and no associated service cost is involved.
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Modern discrete analyzers use xenon source lamps that cover the ultraviolet-visible (UV-VIS) spectral range. In this case, a xenon flash lamp operates only for the duration of the actual measurement, it boosts the lifetime of the lamp and improves the total cost of ownership.
Discrete analyzer – simultaneous and parallel analysis
The option to perform simultaneous and parallel measurements of pH, conductivity, or bitterness of beer considerably improves the lab’s throughput. Entry-level discrete analyzers provide only photometric measurements. Advanced integrated discrete analyzers like the Gallery and the Gallery Plus systems provide the option to expand with electrochemistry unit (ECM) for parallel pH and conductivity measurements. pH is a critical parameter for wine, beer, and other beverages, as well as drinking water and sewage water. The ECM unit can measure 67 samples per hour for pH and conductivity in parallel and simultaneously with other photometric measurements. Simultaneous and parallel pH and conductivity measurements help to consolidate the overall wet chemical analytical needs and enhances the lab’s productivity.