ICP-OES is a very important instrumentation in our laboratory, the principle of ICP-OES, application areas, pre-treatment and common problems, take a quick look.
Inductively coupled plasma atomic emission spectrometry (ICP-OES), a spectroscopic analysis method using inductively coupled plasma moment as the excitation light source, has the advantages of high accuracy and precision, low detection limit, rapid determination, wide linear range, and simultaneous determination of multiple elements, etc. It has been widely used for the determination of dozens of elements in environmental samples and samples of rocks, minerals and metals.
ICP-OES working principle
ICP-OES is a common method to determine the elemental content of a sample. It works as follows: the sample to be tested enters the central channel of the quartz torch tube plasma through the aerosol formed by the spray, and the spectral lines radiated after excitation by the light source, through the incident slit to the dispersion system grating, and the spectral lines of the element to be measured are projected onto the CCD after spectroscopy, and then processed by the circuit, and the data processing is performed by the computer to determine the elemental content.
Background
ICP-AES is known as Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES), also known as Inductively Coupled Plasma-Emission Spectroscopy (ICP-OES). It is mainly used for qualitative (presence or absence) and quantitative (how much) analysis of elements in samples, and can analyze more than 70 elements in the periodic table of elements.
The powerful quantitative functions of ICP-AES are widely used in the analysis of sample elements in the fields of nano, catalysis, energy, chemical, biological, geology, environmental protection, medicine, food, metallurgy, agriculture, etc.
Instrument Principle
Inductively coupled plasma emission spectrometer (ICP-OES/AES):
The plasma excitation light source is used to vaporize the specimen and dissociate or decompose it into atomic states, which can be further ionized into ionic states, and the atoms and ions are excited to emit light in the light source. The light emitted from the light source is decomposed into spectra arranged by wavelength using a spectroscopic system, and the spectra are later detected using photoelectric devices. The specimen is analyzed qualitatively according to the measured spectral wavelength and quantitatively according to the intensity of the emitted light.
Works as follow:
The sample to be tested enters the central channel of the quartz torch tube plasma through the aerosol formed by the sprayer, and the light is radiated by the heating and excitation of the light source, which is diffracted by the grating, and the characteristic spectral line of the element is accurately located at the exit slit by the stepping motor rotating the grating, and the photomultiplier tube transforms the intensity of the spectral line into the photocurrent, which is then processed by the circuit and processed by the computer for data processing to determine the content of the element.
The injection system and ion source of ICP-MS are essentially the same as those of ICP-OES and the light source. Only after most of the atoms are converted into ions, the ions are separated according to the charge to mass ratio and the number of various ions is counted.
The ICP-OES method is mainly composed of two parts: sample pre-treatment and on-board testing, of which the workload of sample pre-treatment accounts for 90%-95% and on-board testing accounts for 5%-10%. This shows that the main difficulty of the method lies in the sample pre-treatment. Here, we will share the tips and precautions of sample pre-treatment process with you, taking soil samples as an example.
ICP-OES pre-treatment
Handling containers
Nowadays, we usually use 30mL PTFE crucibles as containers for dissolving samples. Before use, it is first scrubbed with decontamination powder and then placed in a solution of hot nitric acid with a concentration of 20-30% for 2-3 hours. Next, it is soaked in slightly boiling water for 2 hours. Finally, take it out and wash it 3 times with secondary deionized water. After the above operations, the cleanliness of the PTFE crucible is ensured to avoid sample contamination.
Weighing samples
Number the crucible before weighing the sample. When weighing the sample, weigh it accurately according to the method, paying attention to the order in which the samples are arranged and remembering not to reverse or tamper with the numbers. After weighing, rinse the crucible walls with a wash bottle (rinse the sample that has stuck to the crucible walls during weighing to the bottom of the crucible to avoid sample loss).
Digestion samples
We detect copper, lead, zinc, manganese, vanadium, titanium, chromium, cobalt, nickel and other elements in the soil, generally using the “four acids” dissolution method, the so-called “four acids” is nitric acid, hydrofluoric acid, perchloric acid and hydrochloric acid.
Usually, nitric acid, hydrofluoric acid and perchloric acid are added first in the amounts of 5 mL, 5 mL and 2 mL. After the acid is added, the crucible lid is covered and the temperature of the electric heating plate is set to 180°C. The electric heat is placed to start heating from low temperature.
Care needs to be taken here to heat from a low temperature, as the temperature of the hotplate is too high and the confusion in the crucible is consumed too quickly for the sample to be fully digested. Add the lid to ablate for about 2 hours, close the electric hot plate and leave it overnight.
After that, the lid needs to be opened and the open mouth is heated for digestion until the mixed acid solution bubbles dry.
Then add 10 mL of aqua regia at a concentration of 1:1, and after the salts in the sample are dissolved and the solution is clear, the volume is fixed.
When fixing the volume, rinse the crucible 2-3 times with deionized water.
Resting samples
After the samples are fixed, shake them well so that the components to be measured are uniformly distributed in the solution. The samples are allowed to stand for 3-4 hours before the measurement is carried out on the machine. The purpose of standing is to allow the salts to settle to the bottom of the solution to be measured and to avoid clogging of the ICP-OES injection system during the test. If there are individual samples that need to be tested urgently, they can be filtered and measured directly on the machine after the resting period.
Pre-treatment is the most tedious and time-consuming step in the analysis of a sample, which directly affects the test results. Therefore, we have to master and optimize the sample pre-treatment process in the actual analytical testing work, so as to improve the production speed and ensure the quality requirements.