Optical cuvettes, cleaning

With some modifications as described below, the detailed procedure of Beers and Sizer follows closely the methods we have used and is to be recommended, particularly their method of carefully cleaning the cuvettes to avoid bubble formation, and the method of tracking the optical density changes (for more details see (18)). 

Cuvette material Optically clean glass Electrode cell material Organic glass... 

Never clean cuvettes or any optically polished glassware with ethanolic KOH or other strong base, as this will cause etching. All cuvettes should be cleaned carefully with 0.5% detergent solution, in a sonicator bath, or in a cuvette washer. 

Fig. 85. Precision turbidity photometer TK 3 1) = Outlet 2) = Lamp 3) = Optical system 4) = Tubular cuvette 5) = Cleaning access cap 6) = Reference cell 7) = Interference filter 8) = Measuring cell 9) = Inlet...

The importance of clean cuvettes is self-evident. Routinely, all non-disposable cuvettes should be emptied immediately after use, rinsed repeatedly in the solvent (e.g. water), then with clean ethanol or acetone and dried with low pressure air or nitrogen from a cylinder. It is prudent to install a filter (such as those with pore sizes of 0.45 pm used in filter sterilization) in the gas line. Cuvette washers (e.g. Aldrich) wash, rinse, and dry cuvettes. Cotton wool buds can also be usefiil for dislodging interior, stubborn marks and for drying. The outside optical surfoces should be polished with clean lens tissue. Note that plastic squeety bottles generally used for solvents contain plasticizers such as butyl phthalate, which can interfere with critical UV spectra. 

Adsorption Kinetics of the PLL- -PEG Monolayer by Optical Waveguide Lightinode Spectroscopy (OWLS). The protocol for in situ study of PLL-g -PEG adsorption kinetics by OWLS was as follows Clean waveguides were initially placed in 10 mM HEPES buffer solution for 5 h. Prior to assembly of the flow-through cuvette in the OWLS instrument, the samples were rinsed with water and dried under nitrogen. These presoaked samples equilibrated and reached a flat basehne in HEPES solution in less than 1 h. The samples were then exposed in situ to the PLL-g-PEG solution (1 mg/mL in HEPES buffer solution). The adsorption was subsequently monitored for 1 h. Then the PLL- -PEG solution was replaced with HEPES solution, and surface coverage was monitored for another 30 min. 

First of aU, it is necessary to carefully handle the cells to avoid to scratch or even only to touch the optical surfaces since any imperfection, including an imperceptible fingerprint, can absorb or diffuse light. It is therefore important to always accurately clean the outside of the cells with specific tissues or papers suitable to clean photographic instrumentation components and, in case, with some ethanol for glass or quartz cells, so as the stopper and the hole cone, if present. Moreover, when successive measurements are needed the cell must be placed in the holder always in the same direction, to be sure that the intrinsic optical effects of the cuvette influence all the measurements to the same exact extent. 

There is a large range of optical cells available for spectroscopy measurements and they vary in materials, size, shape, and spectral transmission characteristics. The most commonly used sample holder in fluorescence spectroscopy is a 10 mm x 10 mm x 45 mm volume cuvette made from fused silica (for UV to near-lR operation), glass (visible), or a plastic that is often polycarbonate and disposable. Of course, it is essential that the cuvette chosen is suitable for the application and experiment and that it is clean, and handled with maximum care. 

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