A photoelectric colorimeter is an optical device that is designed to accurately measure the concentration of various substances in solutions.
The principle of operation of the installation is based on the ability of colored liquids to absorb the light beam passing through them. Moreover, the more coloring components are in the solution, the stronger the absorption occurs. The result fixes the device, passing the final data to the laboratory assistant.
Classification and features
In addition to the fact that all models are assigned their own price due to the peculiarities of the pricing policy of each brand, there are several other options for classifying according to professional criteria. We are talking about the division of aggregates into visual and objective types. The second option is still occasionally called photovoltaic.
Visual modifications differ from analogues in the angle of light penetration. Here, the beam passing through the studied liquid illuminates only one part in the field of view. Light only falls on the second half, which is caused by the passage through the solution of the same agent that was evaluated earlier, and its concentration is thoroughly known.
In such a scenario, a comparative result is taken as the basis, which is achieved by analyzing the thickness of the first layer when compared with the intensity of the light flux. After the laboratory assistant successfully achieves a generalization of the color tones of both parts of the visual field, it turns out to derive a schematic relationship. The result will please with relatively accurate information regarding the percentage of concentration in the test solution.
Depending on whether a digital device or its more primitive versions were involved in the study, the level of accuracy will fluctuate. But on an industrial scale, fairly accurate installations are used, which have proven themselves well, taking into account the connection of high-quality light filters. We are talking about modern analogues of classical visual colorimeters – photoelectric colorimeters.
Their work will please with increased accuracy in relation to outdated mechanisms, for which innovative photocells should be thanked. Most often, the manufacturer uses selenium and vacuum radiation detectors for such purposes. With their help, it turns out to achieve almost the same accuracy that the first spectrophotometer offered, but at the same time not spend money on more expensive purchases. Also, the technical data sheet of such advanced equipment for laboratory research provides for the following improved items:
- photoelectronic format multipliers;
- photoresistors;
- photodiodes.
To determine the strength of a particular photocurrent, it is necessary to use the intensity values of the light radiation incident on them. So the specialist measures the degree of absorption of light by the dissolving particles, which indicates the percentage value of the concentration of the test solution.
In addition to standard photoelectric colorimeters with conventional current readings, compensation class colorimeters are widely represented on the medical equipment market. Their optical design is somewhat different due to the difference in signals that correspond to the standard and the studied solution. The local mark is reduced to zero, which was achieved using an electric or optical compensator. The beginning of measurements in this scenario is made with a compensation scale.
It is believed that the presented technique helps to conduct a better analysis, since the error indicators do not respond to:
- conditions of environmental changes such as temperature fluctuations;
- unstable properties of the elements of the technology itself.
But for increased detail, you have to “pay” with the fact that the tool does not provide results directly. Instead, you have to verify the information received by switching to graduated graphs. They are obtained by measuring solutions with already studied concentration properties.
Areas of use
Instructions for using the different categories of colorimeter are quite simple for experienced clinical or research diagnosticians. It does not take much time to install the main nodes with the proper skills. Even the accuracy provided by the latest modifications of the equipment will please with good results, no worse than the complex tactics of a full-fledged chemical analysis provide. The lower frames for measuring the concentration vary in a radius of 10−3 to 10−8 mol / l.
The generalized exploitation algorithm involves only a few steps. First, a cuvette filled with a control liquid with already known indications will need to be rearranged into the light beam. Then, in mechanical mode, it is necessary to rotate the handle of the existing circular photometric wedges. When the galvanometer pointer is set to zero, the movement stops.
A light beam is directed to the cuvette with the control agent. At the same time, the galvanometer needle begins to deviate from its usual position. The laboratory assistant will have to fix the specified value.
Then it remains only to turn off the apparatus and put the used cuvettes in order for the next test.
Against the background of such a simple scheme, it becomes clear why the device is in demand in various fields of industrial and clinical applications. The technique is one of the most indispensable formats of medical equipment that helps to carry out operational measurements of hemoglobin. It is also necessary to assess the current level of total and direct bilirubin, cholesterol, total protein, uric acid.
Its algorithm is readily used by medical laboratories involved in the processing of thymol samples, measurements of iron, creatine, glucose, and even lipoproteins.
The technology has found its application in agriculture. Here, without it, the chemical state of water and feed is not monitored. When you need to figure out whether the soil is suitable for crop or livestock production, you also have to involve a photoelectric colorimeter. He can easily determine whether there is an excess of potassium, nitrates, manganese, magnesium or phosphates in the taken sample.
For the same reason, the device is often used by environmental services, as well as control departments in the food processing and chemical industries. In rare cases, the assistance of the installation is required by geologists or biochemists during scientific experiments.
Some ordinary people, who are far from physical and chemical theories, do not always understand the first time why experts equally often use both photoelectrocolorimeters and spectophotometers. These two devices, although somewhat similar, still perform their tasks in somewhat different ways.
Spectral analysis is based on a beam in monochromatic light. In the second case, a polychromatic medium is taken as a basis, which is formed by a special filter. By changing the filters, it turns out to determine the concentration of various components in the same solution with a minimum error.
The factor of simplified operation and relatively low cost in relation to their direct “competitors” adds advantages to photographic equipment.