大家的UV定期校准项目有哪些？下列有何异同？ 1. SPECTRAL SLIT WIDTH (if applicable) When using an instrument on which the slit-width is variable at the selected wavelength, the slit-width must be small compared with the half-width of the absorption band but it must be as large as possible to obtain a high value of I0. Therefore, a slit-width is chosen such that further reduction does not result in a change in absorbance reading.
5. PHOTOMETRIC LINEARITY Materials: A series of solutions of a suitable absorbing compound (e.g. potassium dichromate) spanning the concentration range of interest. The absorbing solutions need to be stable. The concentrations should be regularly spaced (1, 2, 3, 4, 5) rather than doubling (1, 2, 4, 8, 16) in order to reduce the leverage effects when fitting the line. Method: Measure the net absorbance of the solutions against a blank at 235, 313, 257 and 350 nm. Make 3 measurements for each solution. Calculate the mean value and the linearity of the concentration of each solution against the measured absorbance at the control wavelengths.
7. BASELINE NOISE For this test, 2 alternative methods are proposed. TEST 1 Method: Make 61 absorbance measurements with an integration time of 1 second at a wavelength of 500 nm, with no sample in the sample chamber, and calculate the mean. Limits: Mean ± 0.002 Absorbance units TEST 2 Method: Record the absorbance for 60 seconds at 200, 300 and 400 nm with a highly pure, synthetic Quartz block5. The measurement is made against air. Note: If commercial filters are used, the wavelengths and the exact absorption values with the corresponding tolerance limits will depend on the type of filters.
8. PHOTOMETRIC DRIFT Notes: - Photometric drift should be checked at both the Visible and UV region, at appropriate wavelengths. - The limits are in accordance with the user’s requirements (as defined in Level I) and with manufacturer’s specifications. For this test, 2 alternative examples are proposed. TEST 1 Method: As routine test, the drift is measured at 250 nm over a period of 2 hours by using the Time Scan mode of the instrument, with no sample in the sample chamber. Limits: ± 0.001 Absorbance units/h Note: In certain cases, for example when several samples are measured over a long period of time (or when using auto sampler) the drift can also be determined at the wavelength used for the analytical method, in the same way, before the measurement of the samples. TEST 2 Method: Record the baseline for 60 minutes at 500 nm and compare the absorbance with the initial value. Limits: ± 0.002 Absorbance units/h
10.ABSORPTION CELLS Method: The following method for checking cleanliness and gross differences in thickness or parallelism of the windows of optical cells is described in ASTM E275-01 (American society of Testing and Materials), “Standard Practice for Describing and Measuring Performance of UV, Visible, and Near Infrared Spectrophotometers”: Fill the cell with distilled water and measure its apparent absorbance against air at 240 nm for quartz cells and at 650 nm for glass cells. With recording instruments it is desirable to scan over the optical region of interest. The apparent absorbance should be not greater than 0.093 for 1 cm quartz cells (UV region) and 0.035 for 1 cm glass cells (Visible region). Rotate the cell in its holder (180°) and measure the apparent absorbance again. Limits: Rotating the cells should give an absorbance difference not greater than 0.005.
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