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Slit Lamp Improve Signal To Noise Ratio, Increase Stability
Jun 14, 2017

There are many variables that affect the measurement conditions in the atomic absorption spectrometric analysis. When measuring the various measurement conditions of the same kind of samples, the accuracy and sensitivity of the measurement results have great influence. Choose the best working conditions, can effectively eliminate the interference factors, can get the best measurement results and sensitivity.

1. Selection of absorption wavelength (analytical line)

Usually use the resonance absorption line for the analysis line, measuring high content elements, the choice of low sensitivity non-resonance line for the analysis line. Zn is often selected for the most sensitive 213.9nm wavelength, but when the high content of Zn, in order to ensure the linear range of the working curve, can be changed to sub-sensitive line 307.5nm wavelength measurement. As, Se and other resonance absorption line is located in the 200nm below the far ultraviolet region, the flame composition of its obvious absorption, so the flame atomic absorption spectrometry determination of these elements, should not use the resonance absorption line as the analysis line. Measurement of Hg due to resonance line 184.9nm will be strongly absorbed by the air, can only switch to this sensitive line 253.7nm determination.

2. Light collimation in analysis

It is necessary to adjust the emission position of the hollow cathode light to the optimum position of the detector and ensure the maximum measurement energy.

3. Selection of Slit Lamp width

The Slit Lamp width affects the spectral passband width and the energy received by the detector. Adjust the width of the Slit Lamp, the measured absorbance changes with the Slit Lamp width, when there are other lines or non-absorption of light into the spectral passband, the absorbance will be immediately reduced. Does not cause the maximum Slit Lamp width of the absorbance reduction, that is, should be selected to fit the Slit Lamp width. For the simple elements of the line, such as alkali metal, alkaline earth metal can be used to narrow the wide slot to reduce the lamp current and photomultiplier tube to improve the high signal to noise ratio, increase stability. For complex elements such as iron, cobalt, nickel, etc., need to choose a smaller Slit Lamp, to prevent non-absorption line into the detector, to improve the sensitivity and improve the linear relationship between the standard curve.

4. The height of the burner and the angle with the optical axis

The light source of the light through the different parts of the flame on the determination of the sensitivity and stability of a certain impact, in order to ensure the determination of the high sensitivity should be made by the light source of light through the flame in the ground state atomic density of the largest " The The flame of this area is relatively stable, less interference, about 20mm-30mm above the mouth of the burner slot. The appropriate burner height is selected by experimentation by spraying with a fixed concentration of solution and slowly moving the burner up and down until the absorbance reaches its maximum, where the position is the optimum burner height. In addition, the burner can also be rotated, when its seam coincides with the optical axis (0) by the highest sensitivity. When the sample concentration is to be measured, the burner can be rotated to the appropriate angle to reduce the length of the absorption to reduce the sensitivity.

5. Selection of working conditions for hollow cathode lamps

Warm-up time: After the lamp is lit, the atomic vapor of the radiation is generated by the evaporation of the cathode by the evaporation of the cathode. In order to stabilize the transmitted resonant line, it is necessary to preheat the lamp so that the distribution of the vapor layer in the lamp and the vapor thickness are constant. This will stabilize the intensity of the self-absorbing and emitted resonant lines produced by the atomic vapor in the lamp The Usually for single-beam instruments, the lamp warm-up time should be more than 30 minutes in order to achieve sharp radiation light stability. For a two-beam instrument, the ratio of the reference beam and the measured beam changes at the same time, and the ratio is constant, allowing the baseline to stabilize quickly. Before using the hollow cathode lamp, if the preheat 0.5-1.0h in the case of applying 1/3 of the working current, and regular activation, can increase the service life.

6. Selection of the operating conditions of the photomultiplier tube

Daily operating in the photomultiplier tube operating voltage must be selected in the maximum operating voltage of 1 / 3-2 / 3 range. Increasing the high voltage can reduce the sensitivity, improve the signal to noise ratio, improve the stability of the measurement, and extend the service life of the photomultiplier tube.

7. Flame burner operating conditions of choice

Injection volume: select the adjustable volume of the atomizer, according to the viscosity of the sample to select the injection volume, improve the sensitivity of the measurement. Injection volume is small, the absorption signal is weak, not easy to measure; injection volume is too large, in the flame atomization method, the flame cooling effect, in the graphite furnace atomization method, will increase the difficulty of removing the residue. In the actual work, should be measured with the amount of absorbance changes, to achieve the most satisfactory absorbance of the injection volume, that is, the amount of injection should be selected.





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