A variety of automated or semi-automated chemical analyzers are known which utilize cuvettes for the chemical testing of samples placed therein. Generally, a predetermined amount of liquid sample, such as biological fluid is placed in the cuvette which is then transported through the instrument. As the cuvette is transported, the instrument dispenses a quantity of reagent into the sample and monitors the resulting chemical reaction. Such monitoring is generally accomplished through use of an optical means which views the fluid sample through optically transparent portions of the cuvette.
In order to simplify the loading of the cuvettes into the instrument and facilitate their handling by the instrument once so loaded, proposals have been made to provide the cuvettes in the form of a continuous integral strip. The individual cuvettes of the strip are designed to be relatively rigid but the strip itself is provided with sufficient flexibility to ease its transport through the instrument.
Furthermore, by making the cuvettes in a continuous strip form, they can be manufactured relatively inexpensively from suitable plastic material, thereby permitting their disposal after use. This is an important feature since it avoids the requirement for washing the cuvettes after use and avoids any possibility of cross-contamination of fluid samples which could cause erroneous test results. A proposed cuvette system designed to meet these requirements is proposed in U.S. Pat. No. 4,263,256.
In commonly owned copending U.S. patent application Ser. No. 284,842 filed July 20, 1981 and entitles "Cuvette System For Automated Chemical Analyzer", now abandoned, the disclosure of which is hereby incorporated by reference in its entirety herein, there is described a cuvette belt which comprises a matching pair of formed elongated plastic strips which are joined together along corresponding faces thereof to form an integral belt. A series of regularly spaced cavities or chamber halves is formed transversely in each of the corresponding strip faces which define open-topped cuvette receptacles when the belt halves are joined. As described, the cuvette belt is made by forming strip plastic material with a series of regularly spaced transverse (laterally extending) elongated pockets so as to define two integral side-by-side belt halves. The formed strip is then divided longitudinally to separate the belt halves and the belt halves brought into register and joined together to form a completed cuvette belt.
Using such manufacturing techniques, cuvettes may be obtained with superior optical characteristics and dimensional accuracy previously obtainable only through use of injection molding techniques. This is important when optically analyzing samples in the cuvettes for which a precisely defined optical path through the cuvette is required. It is pointed out that it is possible by utilizing cold forming techniques to avoid optical degradation of the material due to heat. Further an optical portion of the material may be restrained by clamping or other forming techniques during the pocket forming operation to avoid stretching or other deformation of portions of the pocket which form the sides of the cuvette. In this manner essentially all stretching of the material during forming is limited to the side walls of the pockets and optical portions thereof are maintained stress-free and with a uniform thickness.
Reference is also made to commonly owned copending U.S. patent application Ser. No. 746,231 filed June 18, 1985, and entitled "Cuvette Belt Manufacture and Process", the disclosure of which application is hereby incorporated by reference in its entirety herein. In that application is disclosed an alternative method for making cuvette belts where they comprise a matching pair of plastic strips, each of which is formed with chamber halves, and which are joined together to form an integral cuvette belt with the chamber halves aligned to form the cuvettes.
According to that method, two strips of plastic material are identically formed with a series of regularly spaced transverse elongated pockets so as to define two integral side-by-side belt halves. The two formed strips are brought into register and joined together to form a composite strip defining two integral mirror image cuvette belts joined by their cuvette mouth ends. The composite strip is then divided longitudinally to separate the cuvette belts.
The present invention is particularly concerned with techniques for joining the formed plastic strips by heat sealing during the manufacture of such cuvettes while retaining the aforesaid optical characteristics.