Precautions for correct selection and use of cuvettes

It has recently been found that the inability to measure or cause measurement errors due to improper selection or use of cuvettes often occurs in experiments, and this problem is easily overlooked by the experimenter. Now let's talk about the correct choices, use and precautions of the cuvette.

1, the correct choice of cuvette

The light transmissive surface of the cuvette is made of a material that is permeable to light in the wavelength range used. Cuvettes operating at 200-350 nm are suitable for the UV region, and quartz or fused silica must be used to make a translucent quartz cuvette. (Note: The fused silica has never been seen before. Only quartz has been used. If there is any oil, you must let it look and open your eyes.) The quartz cuvette can be used in the ultraviolet region. Can be used in the visible area, but the price is generally more expensive, so choose the cuvette according to the wavelength of use, if you do not use the ultraviolet area, use ordinary glass cuvette on the line, one waste is not necessary, two, hey, broken I don't feel bad, haha. The translucent cuvette made of ordinary silicate optical glass can only be used in the visible region of 350 nm to 1000 nm. (It seems to be able to reach 2000nm, but I won't discuss it here).

2, the correct use of cuvettes and precautions

When using a cuvette, the two translucent surfaces should be completely parallel and placed vertically in the cuvette holder to ensure that the incident light is perpendicular to the transmissive surface during measurement, avoiding the reflection loss of light and ensuring optical path fixation. .

The cuvette is generally a rectangular parallelepiped, and the bottom and sides are frosted glass, and the other two sides are bonded by a light-transmissive surface made of optical glass. Therefore, you should pay attention to the following points when using:

2.1 When taking the cuvette, only touch the frosted glass on both sides with your fingers to avoid contact with the optical surface.

2.2 Do not touch the optical surface with hard objects or dirt. When the solution is contained, the height is 2/3 of the cuvette. If there is residual liquid on the optical surface, it can be gently absorbed by the filter paper, and then wiped with lens paper or silk.

2.3 Solutions containing substances containing corrosive glass shall not be placed in cuvettes for long periods of time.

2.4 The cuvette should be rinsed off immediately after use. If necessary, soak in 1:1 hydrochloric acid and rinse off with water.

2.5 Do not place the cuvette on a flame or electric stove for heating or drying in a dry box.

2.6 If there is any doubt in the comparison of the color dish during the measurement, it can be detected by itself. The user can set the wavelength to the actual wavelength used, inject a set of cuvettes into distilled water, adjust the transmittance of one of them to 95% (100% of the digital display), and measure the other transmissions. For example, if the difference between the transmittances is not more than 0.5%, it can be used together.

2.7 Someone used experience:

2.7.1 Soak the cuvette in a 2% nitric acid solution for 24 hours before use, then rinse with water and distilled water, and dry.

2.7.2 Before the colorimetry, put each cuvette into distilled water and compare it at the colorimetric wavelength. 4-8 of the cuvettes with an error of ±0.001 absorbance are selected for colorimetric determination, which avoids colorimetry. The difference in the dish causes measurement errors.

2.7.3 The liquid in the cuvette should be inclined along the rough surface and slowly poured off. Do not flip the cuvette, place the mouth directly on a clean filter paper, blot the remaining liquid, and then rinse the inside of the cuvette with distilled water. Pour off (operating as above) to avoid outflow of liquid, so that the second measurement does not need to wipe the cuvette, so as not to cause errors due to wiping.

3. Washing method of cuvette

3.1 The cleanliness of the cuvette in spectrophotometry is one of the factors affecting the accuracy of the measurement. Therefore, we must pay attention to the choice of the correct cleaning method.

The experience of cockroaches is: If you measure the solution is acid, if it is not clean, wash it with a weak alkaline solution. If you measure the solution is alkali, if it is not clean, wash it with a weak acid solution. If you measure the solution is organic, if not Clean, use organic solvents such as alcohol to wash.

3.2 Look at the literature:

The principle of selecting a cuvette washing solution is that the decontamination effect is good, and the cuvette is not damaged, and the measurement is not affected.

3.2.1 Analysis Commonly used chromic acid washing liquids are not suitable for washing cuvettes. This is because the water-carrying cuvettes sometimes locally heat up in the washing liquid, causing the cuvette bonding surface to crack and be damaged. At the same time, the cuvette washed by the washing liquid is likely to retain traces of chromium, which is absorbed in the ultraviolet region, thus affecting the determination of chromium and other related elements.

It is generally recommended to use a mixed solution of nitric acid and hydrogen peroxide (5:1) for soaking, and then rinse with water. For cuvettes that are difficult to clean in general, the following two methods can be used.

3.2.2 First, the cuvette is invaded into a solution of sodium carbonate (20 g/L) containing a small amount of anionic surfactant, washed with water, and then inoculated in a mixed solution of hydrogen peroxide and nitric acid (5:1). half an hour.

3.2.3 Wash in a fume hood with a mixture of hydrochloric acid, water and methanol (1:3:4).

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