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Photometric noise is an important indicator affecting the UV-Vis spectrophotometer
Key words: photometric noise; UV-visible spectrophotometer; US instrumentation ; UV-1800
First, the impact of photometric noise on analytical test error In photometric analysis, especially in UV-Vis analysis, photo-meta noise (Photomet ricNoise) is one of the most important factors affecting the deviation from Beer's law, and is the source of the main analysis error. If the photometric noise is known to be N, the calculation formula proposed by AJ Owen can be used: Noise error (%) = N × 100 / A, and the relative error ΔA / A of the absorbance in the case of different N is calculated (ΔA is the absolute absorbance) Error, A is the true value of absorbance) and A. Or find the relationship between ΔA/ A and N in the case of different A. At present, some instrument manufacturers and users at home and abroad do not pay attention to the influence of the luminosity noise of the instrument on the analysis test results. Some manufacturers do not give the important indicator of luminosity noise even on the sample. Some manufacturers (technicians) only measure 15min or 30min when testing luminosity noise. These are not correct and are important issues worth noting. The luminosity noise of the UV-Vis spectrophotometer is one of the main sources of analysis error, and it mainly affects or limits the lower limit of the concentration of the sample to be tested. At present, the illuminance noise of the most advanced UV-Vis spectrophotometer in the world is ±0. 0002Abs (peak-to-peak, such as Ca ry5 of Va rian, USA). When the lower limit of measurement is 0.02Abs, the measurement error can reach 1%. There are many high-end UV-Vis spectrophotometers in the country with luminosity noise of ±0. 0002Ab s (peak-to-peak, such as the US company's Lambda900, etc.). These UV-visible spectrophotometers, which have very low photometric noise, are very useful in the research of marine biology and life sciences, or in the analysis of small samples. At present, the domestic UV-visible spectrophotometer has relatively large luminosity noise. Only a very small number of instruments have very small luminosity noise, such as TU-1901 of Beijing Pu's General Motors Co., Ltd., whose luminosity noise is ±0. 0004Abs (peak-to-peak). When the lower limit of the noise limit is 0. 04Abs, the measurement error caused by noise can reach 1%. Therefore, manufacturers of UV-Vis spectrophotometers in China have to work hard to reduce the luminosity noise of the instrument. At present, many manufacturers at home and abroad do not give the luminosity noise of the instrument in the sample, which is not appropriate. Because the luminosity noise of the instrument is not given, the user cannot judge whether the instrument is suitable at low concentration, and whether the sensitivity and accuracy can meet the requirements for use, it is difficult to judge the applicability and reliability of the instrument, and the user will be brought It is a big trouble. Therefore, whether it is a low-end UV-visible spectrophotometer or a high-grade UV-visible spectrophotometer, it should provide users with extremely important key technical indicators of luminosity noise. The luminosity noise of the UV-Vis spectrophotometer is highly dependent on the scanning speed. In general, the noise of an ultraviolet-visible spectrophotometer with a fast scanning speed is certainly large. Conversely, if the noise of an UV-Vis spectrophotometer is small, its scanning speed will not be too fast. Therefore, many manufacturers of high-grade UV-visible spectrophotometers in the world have designed the relationship between scanning speed and photometric noise, and do not make the scanning speed very fast, but make the luminosity noise very large. On the contrary, they will not make the luminosity noise very small, and the scanning speed will be very slow. But at present, some manufacturers in foreign countries have made the scanning speed of their UV-visible spectrophotometer very fast, and ignore the luminosity noise, which is wrong. Because, in general, the scanning speed of the UV-Vis spectrophotometer is not as important as luminosity noise. At least the scanning speed has no effect on the analysis test error. Noise is one of the main sources of analysis error. Second, the representation of luminosity noise Photometric noise is an output signal of the instrument that changes with time, but is random. It is one of the main sources of analysis error of UV-visible spectrophotometer, which directly affects the signal-to-noise ratio and detection limit of the instrument. At present, there are two ways to express photometric noise in the world: one is expressed by absorbance (Abs); the other is expressed by transmittance (%T). Manufacturers of UV-Vis spectrophotometers in Japan and China use transmission ratio (%T), and manufacturers of UV-Vis spectrophotometers in Europe and the United States use absorbance (Abs). It should be said that both can be used. . But it is better to use absorbance (Abs). Because most users use the UV-Vis spectrophotometer, they basically use absorbance instead of transmittance. If the luminosity noise of the instrument is expressed by the transmittance (% T ), when the error is calculated, the transmittance is also converted into the absorbance, which causes unnecessary trouble to the user. Third, the test method of photometric noise UV-visible spectrophotometer photometric noise test, the current international test method is: The instrument is cold-started, preheated 0. 5h, the sample and the reference cuvette are air, set the absorbance It is 0 Abs, the spectral bandwidth is 2 nm, and the wavelength is 500 nm. The instrument was scanned from long wave to short wave for 1 h. Within 1 h, take 10 min of test data, and in the 10 min test data, the maximum peak-to-peak value within that 10 min is used as noise at 500 nm. Key words: photometric noise; UV-visible spectrophotometer; US instrumentation ; UV-1800
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