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Don't underestimate the sample processing of the medium, be careful that the experiment is full! -Huaqiang Electronic Network
In the research report on the culture medium of Shanghai Jinma Laboratory, it is noted that various methods exist for introducing analytical instruments to samples of different states. While many techniques are effective for specific sample requirements, the most widely used and prioritized method involves the introduction of liquid samples into analytical instruments such as atomic absorption spectrometers, atomic fluorescence spectrometers, and plasma emission spectrometers. Proper sample preparation is crucial—don’t overlook its importance, as it plays a vital role in ensuring accurate experimental results.
Liquid introduction offers several advantages when it comes to analytical instrumentation:
1) Solid samples, after processing and decomposition, are converted into a liquid form where elements exist in an ionic state. This eliminates measurement errors caused by the element’s original state and physical properties.
2) During analysis, 0.1–1 g of solid samples are typically weighed and chemically treated, providing good sampling representativeness.
3) Liquid analysis minimizes the evaporation fractionation of elements from solid samples, leading to more uniform evaporation behavior and improved accuracy and precision.
4) The consistent evaporation behavior of elements allows for simultaneous determination of multiple elements.
5) Standard solutions and matrix-matched solutions can be easily prepared using high-purity compounds of each element.
6) Solution atomization enables the measurement of up to 70 elements, while plasma emission spectrometers allow for multi-element analysis at primary, secondary, and trace levels without changing conditions.
However, there are challenges associated with converting solid samples into liquids:
1) Chemical pretreatment increases labor, cost, and resource usage, requiring dedicated chemical treatment chambers.
2) Some chemical treatments demand specialized knowledge and skill.
3) Sample dilution after decomposition (often over 50 times) reduces the absolute sensitivity of elements.
4) Contaminants or salts introduced during chemical treatment may interfere with measurements.
Sample Preparation and Decomposition Requirements
Despite these challenges, liquid introduction remains the preferred method in most laboratories due to its numerous benefits. When preparing solid samples for analysis, the following should be considered:
1) Ensure the solid sample is processed according to specifications (e.g., crushing, sampling) to maintain uniformity and representativeness.
2) The measured elements must be fully dissolved in the solution. Choose a chemical treatment method that is efficient, easy to implement, and suitable for large-scale sample processing.
3) When applying chemical methods, elements can be separated as needed. The goal is to remove interfering matrix components and improve measurement accuracy, but the target elements must not be lost.
4) Avoid contamination throughout the entire process, including sample preparation, laboratory environment, reagents, and vessels.
5) Monitor the total dissolved solids content in the test solution. Excessive levels can cause matrix effects, spectral interference, and background issues. Ideally, the total dissolved solids should be kept below 1 mg/ml (0.1%) to prevent system blockage.
6) For certain samples like corundum, chromite, and zircon, which cannot be dissolved by acids under normal pressure, alkali fusion (dry method) may be necessary. Alternatively, pressurized wet digestion in a closed container is often used, especially with microwave technology, which enhances safety and efficiency.
Common sample preparation methods include acid decomposition (open or closed containers), alkali fusion, and microwave digestion.
Acid decomposition in open containers is the most common method in labs. It is simple and cost-effective but may lead to the loss of volatile elements like As, Hg, Se, and Cd. For plant or animal samples, nitric acid or sulfuric acid is often added before ashing. However, some minerals like corundum and zircon require alkali fusion for complete dissolution.
Microwave digestion has revolutionized sample decomposition, offering faster and more efficient results in a closed system. It reduces reagent use, minimizes contamination, and improves recovery rates.
Alkali metal melt decomposition is commonly used in geological and ceramic samples. Fluxes like lithium metaborate and sodium peroxide help dissolve difficult materials, followed by water extraction and acidification.
Separation and enrichment are essential steps in sample preparation. They reduce matrix interference and improve detection limits. Techniques include volatile compound generation, solvent extraction, ion exchange, and coprecipitation.
In summary, proper sample preparation is critical for accurate analytical results. At Shanghai Jinma Bio, we specialize in optimizing these processes. Contact us for expert guidance and support in your sample preparation needs.