Method for increasing the scratch resistance of plastic cuvettes

Abstract

In the field of consumable materials for automatic analytical instruments, a method for producing transparent plastic cuvettes with increased scratch resistance includes contacting exclusively an outer surface of the transparent plastic cuvette with a liquid comprising at least one surfactant or with a triglyceride and subsequently drying the outer surface such that scattered-light optical properties of the transparent plastic are not adversely affected.

Claims

1. A method for increasing the scratch resistance of a measuring cuvette consisting of transparent plastic, the method comprising: contacting exclusively to an outer surface of the measuring cuvette a liquid consisting of water and at least one surfactant; and subsequently drying the outer surface.

2. The method as claimed in claim 1, wherein the surfactant is selected from at least one non-ionic, one anionic, one cationic, or one amphoteric surfactant.

3. The method as claimed in claim 2, wherein the non-ionic surfactant is a fatty alcohol alkoxylate selected from the group consisting of polyoxyethylene(20) sorbitan monolaurate (Tween 20) and polyoxyethylene(20) sorbitan monooleate (Tween 80).

4. The method as claimed in claim 2, wherein the non-ionic surfactant is an alkylphenol ethoxylate selected from the group consisting of 4-(1,1,3,3-tetramethylbutyl) phenyl-polyethylene glycol (Triton X-45), octoxynol 9 (Triton X-100), and nonylphenol polyethylene glycol ether (Tergitol NP-9).

5. The method as claimed in claim 2, wherein the non-ionic surfactant is an alkyl polyglycoside selected from the group consisting of benzyl-polyethylene glycol (1,1,3,3-tetramethylbutylphenyl) ether (Triton CF-10) and polyoxyethylene polyoxypropylene tert-C12-13-alkyl amine (Triton CF-32).

6. The method as claimed in claim 2, wherein the anionic surfactant is sodium dodecylsulfate or sodium stearate.

7. The method as claimed in claim 2, wherein the cationic surfactant is distearyldimethylammonium chloride or an ester quat.

8. The method as claimed in claim 2, wherein the amphoteric surfactant is lauryl sulfobetaine.

9. The method as claimed in claim 1, wherein the liquid comprises two or more surfactants including at least one alkyl polyglycoside and at least one fatty alcohol alkoxylate.

10. The method as claimed in claim 1, wherein the measuring cuvette consists of a plastic selected from the group consisting of polystyrene and polymethyl methacrylate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a flowchart of a method for increasing the scratch resistance of a measuring cuvette according to embodiments of the invention.

(2) FIG. 2 illustrates a flowchart of a method for providing a bulk good consisting of a multiplicity of measuring cuvettes according to embodiments of the invention.

(3) FIG. 3 illustrates a flowchart of a method for the optical analysis of a liquid in an automatic analytical instrument having a stock container comprising a multiplicity of measuring cuvettes in the form of a bulk good according to embodiments of the invention.

(4) FIG. 4 illustrates an automatic analytical instrument according to embodiments of the invention.

DETAILED DESCRIPTION

(5) The following working examples are intended to illustrate the invention by way of example and are not to be understood as limiting.

Example 1: Preparation of Measuring Cuvettes According to the Invention

(6) To prepare the surfactant-containing liquids, the surfactants according to Table 1 were used.

(7) TABLE-US-00001 TABLE 1 Surfactants used Trade or Surfactant trivial name Manufacturer non-ionic: Polyoxyethylene(20) sorbitan Tween 20 BASF monolaurate Polyoxyethylene(20) sorbitan Tween 80 BASF monooleate 4-(1,1,3,3-tetramethylbutyl) Triton X-45 Sigma-Aldrich phenyl-polyethylene glycol Chemie GmbH Octoxynol 9 Triton X-100 Sigma-Aldrich Chemie GmbH Nonylphenol polyethylene glycol Tergitol NP-9 Sigma-Aldrich ether Chemie GmbH Benzyl-polyethylene glycol Triton CF-10 Stockmeier (1,1,3,3-tetramethylbutylphenyl) Chemie GmbH ether Polyoxyethylene polyoxypropylene Triton CF-32 Stockmeier tert-C12-13-alkyl amine Chemie GmbH amphoteric: Lauryl sulfobetaine Sigma-Aldrich Chemie GmbH anionic: Sodium dodecylsulfate BASF Sodium stearate Sigma-Aldrich Chemie GmbH cationic: Distearyldimethylammonium Sigma-Aldrich chloride Chemie GmbH

(8) Defined amounts of the surfactants in solid form were weighed out and defined amounts of the surfactants in liquid form were taken up using a metering pipette and in each case dissolved in distilled water such that aqueous solutions were obtained with defined surfactant concentrations (percent by volume [% (v/v)] or percent by weight [% (w/w)].

(9) Commercially available tubular measuring cuvettes (circular cross section, internal diameter 7 mm, wall thickness 0.7 mm, height 30.5 mm) consisting of polystyrene or polymethyl methacrylate were each briefly dipped in a surfactant-containing liquid (for ca. 0.5-2 seconds) with the opening facing upwards such that the outer surface was wetted with liquid to just below the upper edge of the cuvette and no liquid was able to enter the interior of the measuring cuvette. After withdrawal from the liquid, the cuvettes were placed on an absorbent piece of blotting paper with the opening facing downwards and dried at room temperature for at least 20-40 minutes.

Example 2: Determination of the Scratch Resistance of Measuring Cuvettes According to the Invention

(10) The measuring cuvettes prepared according to Example 1 were investigated in abrasion experiments. For this purpose, two identically coated cuvettes, i.e., treated with the same surfactant-containing solution, were each fixed tension-free in two holders of a testing device and arranged one on top of the other so that the surfaces of the cuvettes came to lie plane-parallel in the abrasion test. The holder for the upper cuvette is designed to be stationary; the holder for the lower cuvette is arranged on a horizontally movable sample table. During the abrasion test, the upper cuvette was lowered onto the lower cuvette and a test force of 20 N was generated (from an estimate of the practical loading, appearance of scratches can be expected from a force of ca. 1 N). For the sample table on which the lower cuvette had been arranged, a travel path of ca. 10 mm was set and the upper cuvette was traversed by the lower cuvette in one direction twice with a test force of 20 N. The friction traces thereby generated on the surfaces of the upper and the lower cuvette were examined by light microscopy and the increased scratch resistance and resulting improved wear resistance compared to uncoated cuvettes was assessed by the investigator.

(11) It was observed that layered smeared areas with extensive diffusion resulted on the surface of the upper stationary cuvette due to the friction contact, whereas in the lower moving cuvette on the other hand, line-shaped signs of wear formed in the direction of travel which ranged from fine lines up to extensive streak-like damage to the surface. Based on these features, the qualitative estimation of the improvement to the wear resistance (scratch resistance) compared to uncoated cuvettes was undertaken. The following quality evaluations were used: +++ for very good improvement to the wear resistance; ++ forgood improvement to the wear resistance; + formoderate improvement to the wear resistance; forno improvement to the wear resistance.

(12) The results of the qualitative evaluation of the wear resistance of the variously coated polystyrene or polymethyl methacrylate cuvettes are shown in Tables 2 and 3.

(13) TABLE-US-00002 TABLE 2 Qualitative evaluation of the wear resistance of coated polymethyl methacrylate cuvettes Surfactant concentration of the Wear resistance surfactant-containing solution upper cuvette lower cuvette Tween 20, 0.5% (v/v) ++ ++ Tween 20, 1% (v/v) ++ ++ Tween 80, 0.5% (v/v) ++ +++ Triton X-45, 0.5% (v/v) ++ ++ Triton X-100, 0.5% (v/v) ++ +++ Tergitol NP-9, 0.5% (v/v) ++ +++ Triton CF-10, 0.5% (v/v) ++ +++ Triton CF-32, 0.5% (v/v) ++ +++ Lauryl sulfobetaine, 1% (w/w) ++ ++ Distearyldimethylammonium ++ ++ chloride, 0.5% (w/w) Sodium dodecylsulfate, 0.5% (w/w) + ++ Sodium stearate, 0.5% (w/w) + +

(14) Table 2 indicates that with every surfactant-containing liquid tested an improvement in the scratch resistance of the surface of polymethyl methacrylate cuvettes is achieved.

(15) TABLE-US-00003 TABLE 3 Qualitative evaluation of the wear resistance of coated polystyrene cuvettes Surfactant concentration of the Wear resistance surfactant-containing solution upper cuvette lower cuvette Tween 20, 1% (v/v) + + Tween 20, 2% (v/v) + + Tween 80, 1% (v/v) ++ ++ Triton X-45, 3.34% (v/v) + + Triton X-100, 1% (v/v) + + Tergitol NP-9, 1.43 % (v/v) + + Triton CF-10, 0.5% (v/v) + ++ Triton CF-32, 1% (v/v) + ++ Lauryl sulfobetaine, 3.34% + + (w/w) Distearyldimethylammonium + ++ chloride, 1% (w/w) Sodium dodecylsulfate, 1% (w/w) + ++ Sodium stearate, 1% (w/w) + +

(16) Table 3 indicates that with every surfactant-containing liquid tested an improvement in the scratch resistance of the surface of polystyrene cuvettes is achieved.

LIST OF REFERENCES

(17) 100, 200, 300 methods 102, 104 method steps 202, 204, 206, 208 method steps 302, 304, 306, 308, 310 method steps 400 automatic analytical instrument 402 optical measuring unit 404 stock container 406 measuring cuvette 408 device for automatic withdrawal of an individual measuring cuvette 410 receiving position