In the automated wet chemical analysis blog series, this post explicates the automated Photometric methods, Discrete Analyzers and Flow Analyzers. These techniques are based on final photometric detection, but the key difference is how the reagents are dispensed and mixed with the sample before the measurement. Both these photometric-based techniques are commonly used in food, beverage, environmental, drinking water and other industrial applications.
Automated discrete analyzers utilize colorimetric and enzymatic measurements of several analytes simultaneously from a single sample through photometric analysis. The discrete analyzer mimics the operation sequence of lab chemists, such as dispensing samples, mixing reagents, waiting for the reaction to complete, followed by photometric measurement, to provide fast and reproducible results. 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.
After the reagents and samples are prepared, they are loaded onto the instrument. Next, the individual cuvettes are loaded into the incubation chamber, samples and reagents are dispensed to the individual cuvettes and then mixed, and finally undergo photometric detection depending on the absorbance of specific wavelengths of light. Each measurement is done using single discrete cuvettes and this data is then interpreted through integrated software platforms.
Advanced discrete analyzers use disposable cuvettes that eliminates the carryover effect and reduces the reagent consumption substantially. The number of wet chemical parameters a discrete analyzer can perform is limited by the number of filter positions and the wavelength range.
A typical Flow Injection Analyzer (FIA), Continuous Flow Analyzer (CFA), or Continuous Segmented Flow Analyzer (SFA) system consists of an Autosampler, a peristaltic pump, a chemistry manifold, a photometric detector and data acquisition software. In contrast to Flow Injection Analyzer, a segmented flow analyzer employs a continuous flow of samples and reagent, segregated by air bubbles within tubing and mixing coils. Reagents and samples are carried by a multichannel peristaltic pump and mixed in a mixing coil manifold and detected at a specific wavelength.
This setup is commonly referred to as a channel or chemistry manifold. The number of wet chemical parameters a flow analyzer can handle is limited by the number of channels or chemistry manifold. Flow analyzers are ideal when a larger number of samples are to be analyzed for a smaller number of chemistries.
Flow analyzers, being modular, can add additional sample preparation blocks for difficult sample matrices. Some of the flow analyzers can perform inline heating, distillation, dialysis, filtration and digestion. Users could change the measuring pathlength to enhance detection limits. Flow analyzers are suitable for few parameters for many samples.
Major advantages of discrete analyzer overflow analyzers include the number of parameters per sample, lowest reagent and sample consumption, lower cost per analysis, very low or no carry-over, easy to use and maintain, stable calibration and walkaway solution.
Discrete analyzers typically have 5 to 12 filters, equivalent to channels in Flow analyzers and are suitable for multiparameter analysis. The Thermo Scientific™ Gallery™ discrete analyzers has 12 filter positions that allow up to 20 different wet chemical parameters per sample to be tested. The discrete, fully disposable, cuvette technology allows laboratories to measure multiple analytes simultaneously while reducing total analysis and operator time. The unique low-volume cuvette design accommodates small reagent volumes and minimizes reagent consumption compared to flow analyzers.
Integrated discrete analyzers, such as the Thermo Scientific™ Gallery™ discrete analyzers, can automate photometric (enzymatic, colorimetric, turbidimetric) and electrochemical (pH and conductivity) measurements providing fast, reproducible results in a compact, benchtop design.
The flow analyzers are batch analyzers, meaning they are particularly suitable for analyzing few parameters for a large number of samples. A specific channel or manifold requirement limits the number of wet chemical parameters they can test per sample. Typically, flow systems test two to max six different parameters per sample. Increasing the number of channels increases the cost of the equipment proportionately. If a laboratory is looking for an easy to use high throughput, expandable, multiparameter, wet chemistry analyzer for large numbers of samples, then integrated discrete analyzers are better suited than any type of flow analyzers.
In addition, apart from the technology type, wet chemical analyzers should be selected based on other factors, such as:
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