Cuvette

A cuvette ( cuvette from French ) is a vessel with plane- parallel faces, which is used for optical studies (UV / VIS spectroscopy) used, for example as a resonator in dye lasers. Cuvettes are available in different qualities, depending on its purpose. Usually they consist of glass or plastic. For wavelengths below 200 nm cuvettes made ​​of quartz glass are needed. A special form of the cell is the Fotoküvette used in the aquarium hobby. The simplest cell consists only of two sheets of glass - no spacers - allows layer thicknesses in the micrometer range, without dilution and is responsible for the visual comparison of strongly light absorbing liquids such as blood, cosmetics or heavy fuel oil suitable.

Classification

Cells are classified according to:

• The glass ( depending on the desired transmittance and resistance )
• The layer thickness (for example, normal and microcells with or without spacer)
• The construction ( in collapsible, compact and disposable cuvettes )
• The physical state of the sample ( in liquid and gas cells )
• Of sample feed ( in flow-through cells and cuvettes for manual sample introduction )
• The measurement accuracy ( in routine and precision cuvettes )

Cell

As Cell analysis methods are referred to, with which chemical parameters of solutions can be measured photometrically. The solution is caused by specific for the parameter of interest reagents for reaction. By this reaction is a modification of the color or other optical properties of the solution. These changes can then be measured photometrically. They are directly related to the concentration of the investigated substance in the solution and therefore allow quantitative statements.

Often so-called disposable cuvettes are used, which already contain the necessary reagents in the right amount. It only a defined amount of the test liquid is then introduced (e.g., water ) to the cuvette, and after mixing, the reaction begins. Depending on parameters surveyed, the reaction time is a few minutes to several hours, sometimes heated (e.g., when COD ) or the addition of other reagents in the course of the reaction is necessary. After completion of the reaction, the photometric measurement can be performed. Commercial providers of cell tests offer this photometer devices with microprocessors, convert the measured absorbance immediately at this concentration value and show what digital.

Cell tests are used because of their speed and ease of use, inter alia, in water analysis. Examples are environmental and food processing plants, such as sewage treatment plants, water plants, breweries and dairies. Another area is the HB- rapid test for blood donations.

Flow-

In flow cells, the sample is not pipetted and removed after the measurement. Rather, the sample through a tube in the cuvette is performed by the measuring chamber and back out of the cell also. As long as the connected pump is running, the sample constantly the name flows through the cell, therefore flow cell. These are commonly used for tablet dissolution testing. These tablets dissolution test is examined, when the active ingredient of a tablet in the course of the dissolution release in the stomach.

Blistering

Air bubbles, which are located throughout the measurement in the measuring chamber, can lead to incorrect measurements. This is observed predominantly in cells with large layer thickness and round aperture.

Flow rate (flow rate )

The flow rate depends on the cross section of the feed hose, the smallest cross section in the cuvette of the performance of the attached pump, and not least the nature of the sample itself ( viscosity).

Beam cross section

Especially at very small apertures is to ensure that the light beam cross-section is in the center of the measuring chamber. It should be smaller than the measuring chamber, so that neither the bottom nor the side walls to be touched.

Measuring chamber

The cross section of the measuring chamber is either rectangular or round in flow cells. Through the use of black glass or black quartz glass in the measuring chamber to ensure that no foreign or false light affects the measurement. The black frame around the measuring chamber takes over the function of a diaphragm.

Cleaning

Flow-through should also be cleaned only in the flow. To the inlet of the cell is connected via a pump to a reservoir with special Küvettenreinigungsmedium. The hose from the drain it also leads in the reservoir. From ultrasonic cleaning must advise against it, since the ultrasonic waves destroy the highly precise window or even able to bring the entire cell to burst.