Inductively Coupled Plasma Mass Spectrometry(ICP-MS), is an analytical technique for analyzing the chemical properties of elements in materials, and became a mature analytical method in the 1990s. It can accurately qualitatively and quantitatively determine almost all elements in the periodic table, including refractory elements, and has a wide range of analysis.
It can analyze multiple elements at the same time and effectively provide elemental composition information. It can also be used for isotope analysis of analyte elements, widely used in isotope dilution quantification and stable isotope display.
It can determine the analyte elements at extremely low concentrations, and the lower limit of quantification reaches 1~10ng/L. Response sensitivity is higher than most other modern analytical instruments.
The sample introduction system is an important part of ICP-MS, which has a great influence on the analysis performance. However, ICP-MS has high sensitivity and most analysis schemes analyze a wide range of trace elements, so special attention should be paid to contamination loss during sample preparation.
Sample preparation processes such as sampling, storage, sample preparation, decomposition, separation, pre-precipitation, contamination or loss of analyte elements are the most important systematic errors. The lower the concentration of the element to be measured, such as as low as mg·kg-1 or even ng·kg-1, the more obvious the impact of pollution and loss.
The primary sources of pollution include the materials of the utensils and tools used, the reagents and the experimental air environment. The material of the utensils and tools used in the experiment is extremely important in trace analysis. Contaminants may leach from vessels or tools, or impurities from their surfaces may desorb into the sample solution.
Materials recommended for use in trace analysis fall into the following categories:
1. Silica glass, especially artificial quartz, has high purity and is one of the best materials for trace analysis. The main advantages are: not easy to be polluted, smooth surface and poor adsorption, can withstand high temperature of 1200 ℃, and can withstand most inorganic acids, except HF and H3PO4.
2. Polyfluoride, PTFE, PFA and TFM are preferred in the digestion process. Due to the non-polarization of the surface, the adsorption of polar ions is minimal, so the pollution and loss caused by adsorption or desorption are very small. The maximum temperature resistance is 260°C. The advantage is that these materials are resistant to almost all inorganic acids and can therefore be used for HF digested samples. PFA and PTFE have the same excellent physical and mechanical properties, electrical properties, chemical stability, non-stickiness, flame retardancy and atmospheric aging resistance. Although the melting point of PFA is lower than that of PTFE, its long-term use temperature is the same as that of PTFE, and its mechanical strength at high temperature is better than that of PTFE. And the outstanding feature of PFA is that it has good thermoplasticity and has no processing difficulties like PTFE, so it is called meltable polytetrafluoroethylene. PFA can be processed by molding, extrusion, and injection molding. Here, it is more recommended that the container made of PFA is used as the digestion container for sample pretreatment.
The same container made of PFA, due to different production and processing methods, will lead to a long or short service life of the product; different grades of raw materials selected will also lead to different degrees of impurity precipitation during long-term storage of reagents; due to the good processing performance of PFA, it is recommended to choose When using PFA containers, it is also necessary to check whether they are made of recycled materials. Once PFA products made of recycled materials are accidentally purchased and used, the consequences of contamination to the sample will be immeasurable.
All PFA products produced by our company not only resolutely eliminate the use of recycled materials, but also ensure the use of the highest grade raw materials. Even if various highly corrosive reagents and samples are stored for a long time, or samples are digested, there will be no impurities.
Another significant source of contamination is surface-adsorbed impurities. It is usually necessary to fully clean the used container before using it. For example, an acid countercurrent cleaner uses acid vapor (usually HNO3) to clean quartz material containers, borosilicate glass, PTFE, PFA, TFM and other material containers.
Another example is the cleaning of polymer material containers:
① Removal of polymer surface residues;
② Rinse with deionized water;
③ Put it in a PFA large-capacity cleaning tank, fill it up with 1:4 HCl, soak it, and leave it for at least 1 week
④ Rinse with deionized water;
⑤ Put it in a PFA large-capacity cleaning tank (representative product: Nanjing Binzhenghong 4L large-capacity PFA cleaning tank), fill it with 1:4HNO3, soak it, and leave it for at least 1 week
⑥ Rinse with deionized water;
⑦ Dry. The cleaning process of polytetrafluoroethylene containers is similar to that of polymer containers, except that the concentrations of HCl and HNO3 used are 1:1 and kept at 80-90°C for at least 4 hours.
Appropriate utensils and correct cleaning methods can minimize the interference of pollution on ICP-MS and obtain ideal analysis results!