Calibration and maintenance of ICP spectrometer

Inductively coupled plasma optical emission spectroscopy (ICP-OES) is an important method for the analysis and detection of inorganic components in the laboratory. It has become a geological, metallurgical, environmental and other sectors due to its wide linear range, sensitivity separation, and simultaneous determination of multiple elements. In the past two years, the new models of ICP-OES have been characterized by miniaturization, integration, humanization and intelligence. Because it is a precision instrument, it should be especially careful in the correction of the use of the instrument and the maintenance of peacetime.

1 , ICP spectrometer calibration method

(1) Wavelength correction and analysis correction

The wavelength correction is to match the actual wavelength to the detected wavelength of the detector. It can be roughly divided into two parts: firstly, the instrument is calibrated by adjusting the instrument, and then drift compensation is used to reduce the displacement of the line due to environmental changes. Spectral correction is the correction of the deviation between the actual measured wavelength and the theoretical wavelength of the instrument. It is generally corrected by testing the wavelengths of a series of elements. The corrected data is the corrected data for correcting the spectrum. The drift compensation is because there is a nonlinear function relationship between the spectral line displacement of the optical spectrum and the wavelength, temperature, humidity, and pressure changes. This functional relationship has universal applicability. Among them, the zero-order spectral line has the largest displacement due to wavelength and temperature changes. Drift compensation is a routine monitoring process. The principle is to monitor multiple hydrogen wavelengths during the injection interval, compare the actual value with the theoretical value, and compensate for the error.

(2) Analytical correction

The analytical correction is to establish the relationship between the measured element concentration and the light intensity detected by the instrument. It is often said that the standard curve is used, and the standard value of the standard is pre-configured, and then the instrument is tested to allow detection. A relationship curve is established between the value and the concentration, and the unknown sample concentration is obtained according to the curve and the concentration; In the middle of the bifurcation of ICP-OES, there is a linear relationship between the measured value and the concentration. In actual work, when there are other element peaks that interfere with the measured element peaks, the error can be reduced by adjusting the calculation method and the flame observation method to improve the linear correlation coefficient. Here we need to explain the necessary and insufficient conditions for the linear correlation coefficient to be accurate.

2 , ICP spectrometer maintenance

(1) ICP spectrometer use environment

As with other large precision instruments, the operation of ICP spectrometers also needs to be carried out under certain circumstances. These conditions are not met, not only the use of the instrument is not good, but also the detection performance of the instrument, and even damage to the instrument. Affect the life of the use. As mentioned above, when drift compensation is mentioned, there is a nonlinear function relationship between the spectral line displacement of the spectrometer and the wavelength, temperature, humidity, and pressure changes. Therefore, if the temperature changes too much, it will result; the data is unstable, we generally require The room temperature is maintained at 2a ° C and the temperature change should be less than ± 1 ° C. Excessive humidity in the studio can also damage optical components, especially gratings, which are susceptible to moisture damage or performance degradation. Humidity is also very important for some electronic and electronic components, especially for high-frequency generators. If the humidity is too large, it may cause the plasma to be difficult to ignite, or even high-voltage power supply and discharge destroying components of high-voltage circuits, such as impedance matching of the output circuit. The variable capacitor in the network discharges, and the power tube is blocked by a straight ceramic capacitor. The instrument description indicates that the humidity should be no more than 70%. In actual work, we have kept the instrument working humidity at 50%.

(2) Power supply for ICP spectrometer

In order to ensure the safe operation of ICP-OES, the power supply line of the instrument should have sufficient capacity to ensure that the instrument will not operate due to excessive voltage drop, which will cause damage to the instrument and affect the life of the instrument. By installing an automatic voltage regulator or a magnetic saturation regulator to achieve the voltage requirements of the instrument, the supply voltage is generally required to vary by no more than +5V. The power supply line of the ICP spectrometer can be pulled up separately, as far as possible without a large fan. Large electric equipment such as air conditioners, large motors, muffles, etc. share a power supply line, so as to avoid excessive fluctuation of the power supply line voltage when these equipments start, resulting in unstable instrument operation. Ground the instrument with a current greater than 30 amps.

(3) Maintenance of the gas control system of the ICP spectrometer

First, do a gas test, turn on the gas switch of the gas control system, put the solenoid valve in working condition, then open the gas cylinder and pressure reducing valve, so that the gas pressure is indicated at the rated value, then close the gas cylinder and observe the pressure reducing valve. The pointer of the pressure gauge should not fall or fall very little within a few hours, otherwise there will be air leakage in the airway, which needs to be checked and eliminated. At the beginning, the carrier gas flow rate is increased, the injection volume is increased, the amount of entering the ICP is naturally large, the intensity of the line is increased, and the letter-to-back ratio is increased. However, after a certain value has passed, the carrier gas is increased again, and the speed is too fast, so that the particles entering the ICP are not excited and rushed out of the ICP, and the carrier gas having a large flow rate also lowers the ICP temperature. In this way, the emission intensity will also decrease, and the letter-to-back ratio will also deteriorate. It is worth mentioning that the carrier gas flow also affects the best observation height. In general, an increase in flow will increase the optimal height of observation, for the same reason as before. The air compressor, the air filter drains, and the filter and air tube are placed in a cold place to reduce the chance of failure.

(4) Nebulizer and optical system maintenance

The nebulizer is the most precise and critical part of the injection system and requires excellent maintenance and use. After the sample is measured, especially after the high salt solution is measured, the top of the atomizer and the torch nozzle will have a salt accumulation, which will result in a poor passage of the aerosol, and the intensity of the detected element will generally decrease. Generally, we remove the atomizer and immerse it in concentrated nitric acid for one night. Pay attention to the atomizer, the b capillary is completely immersed in the acid solution, and there is no air, then use the water in the injection direction. Wash thoroughly and dry. Be careful not to use an ultrasonic cleaner. Optical initialization is an important guarantee to ensure the sensitivity of the analysis and the stability of the reading. Before the quantitative analysis, when the instrument prompts to run the optical initialization, optical initialization must be done first.

(5) Others

Before each start-up, you should plan the experimental plan in advance, and prepare for it to avoid repeated start-up during a period of time. ICP-OES is a -T- cake, and frequent startup can cause damage to the instrument, because each time it is turned on. The current that passes through it instantaneously is much larger than the current during normal operation, which may cause premature aging of some components. Even if there is no sample to do, you should ensure that you open the week-- Times. After each experiment, be sure to keep the sample and other solutions away from the instrument to reduce the corrosion caused by the evaporation of the solution. The cooled circulating water is preferably distilled water to prevent fouling.

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