The Technicon Auto Analyzer II


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Introduction

The auto-analyzer (automated analyzer) is a set of modules connected in sequence to perform an automatic chemical analysis. It can replace the step-by-step time consuming procedure of manual analysis in research laboratories, hospitals and industry. The auto-analyzer can be used to analyze air, water, waste effluent, soil, metal, and samples of pharmaceutical, agricultural and biological materials. In agriculture, the auto-analyzer is generally used for determing levels of nitrates, nitrites, and ammonium in plant, soil, and water samples.

The operation of this instrument is based on the concept of continuous flow which allows for flexibility and versatility in chemical analyses. Using a combination of different modules makes it possible to automize a variety of wet-chemical procedures such as the following: mixing, coagulation, filtering, liquid-liquid extraction, incubation, concentration, homogenization, precipitation, decanting, dialysis, distillation, hydrolysis, column chromatography, and wet chemical pyrolysis.

The chemical reactions take place in a flow of liquid-air stream, which is controlled by the pump and sizes of plastic tubing from module to module. Different analytical functions such as sampling of unknowns and standards, metering of reagents, purification and filtration, heating and incubation, or detection and recording are carried out in each module. Specific analyses require particular sets of "manifold" tubing, glass connectors, mixing coils, pump tubing, etc., depending upon the procedure.


Theory

The colorimetric determination of the auto-analyzer is based on the Beer - Lambert's Law. This law states that the absorbance (optical density) of a substance is directly proportional to the concentration of that substance. This means that a change in concentration of a sample will cause a change in color intensity, changing the optical density of that substance. According to this law a graph of absorbance versus concentration is used to calculate the values of concentration for samples under analysis by the following equation:

Cu= Au/As * Cs

where:

A= log Io/I

Using absorptivity as a mode to express the relationship between light energy, sample concentration and sample thickness (ligth path length):

a=A/bc

The absorbance of all colored solutions is determined at different wavelengths. A wavelength is chosen in the substance analysis to give an optimum sensitivity (closest approximation to Beer - Lambert's Law ). However it is common and significant to have deviations from the Beer - Lambert's Law linearity because of several factors such as ambient light, improper filters and chemical errors (uncontrolled pH, temperature variation, presence of impurities and improper pre-set parameters).


Apparatus Constituents

The Technicon AutoAnalyzer II consists of the following components:

Sampler

The sampler consists of a sample tray and a metal probe. The sample tray holds the cups that the sample is poured into. The tray on this model can hold up to 40 cups. The loaded sample tray rotates and the metal probe dips into each cup and aspirates a portion (1ml or less) of the contents for a given time interval. The probe rapidly lifts out of the cup, aspirates air for approximately one second, and goes into a wash receptacle where diluent water (a rinse water consisting of 1 ml Brij-35 (a surfactant) to 1 liter of deionized water) is aspirated. Again after a preset time interval, the probe rises from the wash receptacle, aspirates air, and moves onto the next sample cup. This process is repeated until all the samples on the plate have entered the system. The sample tray has a peg which trips a trigger to stop the rotation of the tray and the probe. The sampler is also equipped with an alarm which can be set to sound when the last sample is done. Near the probe wash receptacle is a sampler wheel. The sampler wheel determines the speed of the sampler and the ratio of sample to rinse. The speed and ratio is different for various chemical determinations or assays.


Proportioning Pump

The pump consists of two parallel stainless steel roller chains that carry transverse steel rollers which bear continuously against a spring-loaded platen surface. The platen surface applies pressure to the tubes on the rollers which squeeze the various fluids ahead of them into the system in the exact proportions required by the test. The rate of reagent flow is determined by the diameter of the resilient plastic tubing, the distance between the rollers, and the speed of the rollers. The pump also has a high speed but it is only used for washing out the system after the samples are run if you are in a hurry.


Manifold

The manifold brings together samples and reagents so a reaction can occur and a desired analysis may be performed. Chemicals are mixed by segmented air bubbles in the manifold to form the color complexes necessary for the specific procedure or determination. If a cadmium column is used, air bubbles are introduced into the system then taken out before reaching the column and reintroduced after the column. Some manifolds also contain a heating element which aids in speeding up the reaction. The heating element is necessary for ammonium and TKN (Total Kjeldahl Nitrogen) assays. Each assay has a different flow diagram which shows the necessary tube sizes, coils, flow cell, and connections for the manifold tubing.


Photocolorimeter

The colorimeter measures the intensity and the amount of the light absorbed as the liquid phase flows along the optical path and the phototubes. The filter used also depends on which assay is run. The colorimeter measures absorbance by either direct or inverse operation. In the direct operation the analytical stream undergoes a color producing reaction and in the inverse operation the analytical stream undergoes a color reducing reaction. The absorbance is higher in the direct operation which also means the concentration of the sample is higher and vice versa for the indirect operation.


Recorder

The recorder graphs the absorbance of the liquid flowing past the photocell. The recorder has an on off switch and a paper feed switch, the recorder does need to warm up but the paper feed does not need to be running. The graph paper in the recorder is numbered as to how many feet of paper is left on the roll. The graph paper specifies 'to fit Technicon instrument' but an example of the scale is 0-100.




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