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Single component quantification example - infrared determination of free silica content in dust
Date: 2025-11-24Read: 1
The harmfulness of dust in production environment and SiO in dust2The content of free silica is closely related. Countries around the world consider the content of free silica in dust as one of the important indicators for establishing dust hygiene standards. Dust with a free silica content greater than 10% in the workplace is called silica dust. Long term exposure to silica dust can lead to silicosis, which is one of the most serious occupational diseases in China. In 2014, the State Administration of Work Safety stipulated in Article 14 (2) of the "Work Standards for Occupational Health Technical Service Institutions" (Safety Supervision Department Anjian [2014] No. 39) that for dust with unknown silica composition or dust containing free silica, the content of free silica should be measured to determine the nature of the dust.
Free silica refers to silica that is in a free state without binding to metals or metal oxides. Free silica can be classified into three types based on its crystal structure: crystalline, cryptocrystalline, and amorphous. The determination of free silica content in workplace dust is carried out in accordance with GBZ/T 192.4-2007 "Determination of Dust in Workplace Air Part 4: Free Silica Content", which includes the pyrophosphate method, infrared spectrophotometer, and X-ray diffraction method. The pyrophosphate method is a manual operation that greatly tests the proficiency of experimenters in basic chemical operations. Therefore, it has high requirements for personnel, is time-consuming and cumbersome, and the experimental results are greatly affected by the proficiency of experimenters; The X-ray diffraction method is too expensive and has poor universality for the base layer; Infrared spectroscopy method is easy to operate, fast to test, and accurate in results. The entire process only used a small amount of potassium bromide reagent, which is environmentally friendly and efficient, and currently has strong popularity at the grassroots level.
Experimental Procedure
1. Standard sample preparation: Take approximately 10, 20, 30, 40, 50, and 100 milligrams of alpha SiO2Mix 240, 230, 220, 220, 210, 190, and 150 milligrams of potassium bromide powder (200 mesh) evenly. Then use the mixed powder as a standard sample for sampling.
2. Standard sample spectrum acquisition: Place the uniformly mixed sample and potassium bromide mixture in a compression mold to achieve a transfer rate of over 98%. Stack the mixture transferred to the mold into small mountain samples and then proceed with compression. Take out the prepared sample pieces and place them on the transmission bracket of the infrared spectrometer for absorbance testing. The spectrum is shown in Figure 1.
Figure 1 Infrared absorption spectrum of free silica
3. Establish standard curve: Import the obtained standard curve into the software, select the appropriate absorption peak to establish the model, as shown in Figure 2, α-SiO2At 800, 780, and 694cm-1There are absorption peaks nearby, and we modeled these three peaks separately as shown in Figure 3, Figure 4, and Figure 5, with correlation factors above 0.998. Note that the actual sample may interfere with the absorption peaks, and we should select a suitable absorption peak model to calculate the sample absorption. If the dust contains components such as clay, mica, amphibole, feldspar, etc., 694cm should be selected-1The standard curve of the absorption peak.
Figure 2 Modeling of Free Silicon Dioxide
Figure 3: 800cm-1Standard curve of nearby free silica
Figure 4 780cm-1Standard curve of nearby free silica
Figure 5 694cm-1Standard curve of nearby free silica
4. Quantification of samples with unknown content: Mix the sample and potassium bromide into tablets, and then place them on the transmission bracket of an infrared spectrometer for absorbance testing to obtain the sample spectrum. Then, the standard curve will be retrieved to calculate the content of the unknown sample, as shown in Figure 6.
Figure 6: Using the standard curve to calculate the free silica content of the sample
Summary:
The use of infrared spectroscopy can quickly and accurately detect the content of free silica in dust, safeguarding our health. Welcome to followIRInfrared Cloud Academy, learn more infrared knowledge together. Making more people aware of infrared, knowing how to use infrared, and making good use of infrared are our constant efforts!