1、 The importance of stray light

Scattered light isultravioletVisible spectrophotometerVery important key technical indicators. It isUV visible spectrophotometerThe main source of analysis error directly limits the upper limit of the concentration of the analyzed test sample. When the stray light of a UV visible spectrophotometer is constant, the higher the concentration of the analyzed sample, the greater the analysis error. ASTM believes that "stray light may be the main source of error in spectral measurements. Especially for high concentration analysis and testing, stray light is even more important. There are literature reports that in absorption spectroscopy analysis in the UV visible region, if the instrument has 1% stray light, it will affect 2 When testing samples of 0A, if there is a 2% analysis error, it indicates the presence of this stray light in the instrument. However, it must be noted that when there is a zero point error in the instrument, it may cause confusion. If white is applied to opaque samples, it can increase the reflection and scattering effects of the sample itself, and improve measurement sensitivity. The second form refers to light that deviates from the normal optical path and reaches the photoelectric converter beyond the testing wavelength. It is usually caused by certain defects in the optical system. Such as scratches on the surface of optical components, poor design of the instrument's optical system, poor processing of mechanical components, and displacement of the optical path position.

The impact of stray light on the error of analytical test results increases with the increase of absorbance values. Therefore, the larger the absorbance value, the greater the impact on the error.


2、 The source of stray light

There are many reasons for the generation of stray light, and the main reasons are roughly as follows:

① Dust stains optical components such as gratings, prisms, lenses, reflectors, filters, etc.

② Damage to optical components or other defects generated by optical components (such as gratings, lenses, mirrors, bubbles in prism materials, etc.).

③ Reflection inside the collimation system or related to the edge of the partition.

④ The optical system has poor shielding.

⑤ Secondary electron emission caused by thermal radiation or fluorescence.

⑥ Defects in narrow slits.

⑦ The aperture of the beam does not match.

⑧ Aberrations in optical systems.

⑨ Improper blackening treatment of the inner wall of the monochromator.

Among the above 9 aspects, gratings are the main source of stray light. The stray light it generates accounts for over 80% of the total stray light.

3、 Testing method for stray light

At present, the commonly used method for testing stray light is the so-called't he cut off filter method 'or the' filter r method '. The main method is to use filters or filter solutions to test the stray light of UV visible spectrophotometers. Sometimes the 632.8nm wavelength of He Ne laser is also used to test stray light. The specific method is to conduct the test at a distance of 632.8nm ± 5nm, and the measured values are consistent with 632 Compared to 8nm, it is stray light. The specific testing method for the "cut-off filter method" is to turn on the instrument in a cold state and preheat it to 0 5h , If using the "filter method" for testing, the reference is air; If using filter solution for testing, the reference is solvent (if using nai or nano2 aqueous solution, the reference is distilled water). Set the vertical axis of the instrument to% t and the horizontal axis to wavelength nm. When using a filter solution, fill the sample cuvette with the filter solution and the reference cuvette with the dissolution solution. Adjust the wavelength to the corresponding wavelength (nai is 220nm, nano2 is 340nm) for testing.

The instruments developed and produced by Shanghai Spectral Analysis Instrument use high-performance UV coated lenses,

TU-1901 TU-1901plus TU-1810 TU-1810plus Stray can be controlled within 0.03% T