Analysis of trace sulfur
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The classical method for analyzing trace total sulfur in liquids or gases is undoubtedly the microcoulometry method; however, it is rather complicated to use and its reproducibility is not particularly good； The ultraviolet fluorescence flow measurement technique is more advanced than the microcoulomb method and is also easier to use; however, it is unknown what the analytical accuracy of this instrument is and whether it can replace the coulomb method. I hope friends who have used it can discuss it. Additionally, analyze the total sulfur in gases – which method is more reliable?
There are many methods for analyzing the total sulfur content in petroleum products, but each method has its own characteristics and, of course, its limitations. The total sulfur is determined by the Coulomb method, on the premise that all sulfides are quantitatively or proportionally converted into sulfur dioxide, which is then accurately measured by iodometry in a Coulomb cell. In principle, the Coulomb method is the most accurate, as it is based on the fundamental principles of electrochemical methods; however, due to the numerous factors that can affect its results, it is necessary to use standard samples for calibration. The ultraviolet fluorescence method also requires that the sulfides in the sample be converted into sulfur dioxide in a quantitative or proportional manner; photometric detection is then carried out based on the ultraviolet fluorescence properties of sulfur dioxide. This is a property that is highly dependent on the detection conditions, so the conditions of the instrument or the experiment certainly have a significant impact on the results. These two methods are generally used to determine the trace sulfur content in organic samples, and both require verification and calibration using standard samples; their accuracy is expected to be quite good. The determination of total sulfur in gases is similar, but attention should be paid to the impact of the accuracy and repeatability of gas sampling on the measurement results. Additionally, for liquid samples, particularly the total sulfur content in petroleum products, X-ray fluorescence analysis can also be used, with a sensitivity of up to 1 ppm. If you need information in this area, feel free to contact me.
Chromatography can also be used. Using an FPD detector
Reply to 3# qchgao: I would like to ask you again – are you currently using such an analysis method to determine the total sulfur content in liquefied gas? If so, please share the specific analysis conditions and instrument setup. Another issue is whether chromatographic analysis is still possible if the sulfur content in the liquefied gas is relatively high (around 500) ? I heard them say that it is harmful to the chromatography column and the detector ； If the sulfur content is very low, adsorption becomes more severe, making it difficult to obtain accurate results
The coulombic method is generally used to determine total sulfur, while chromatography is employed for determining the form of sulfur. The FPD detector in chromatography is an appropriate choice; it will not be damaged even when sulfur levels are high. The FPD is a detector specifically designed for detecting sulfur and phosphorus. What type of sulfur is predominant in liquefied gas? Hydrogen sulfide?
To analyze the total sulfur content in liquefied gas, chromatography is currently used; this method involves two injections for analysis, with the total sulfur amount being calculated by adding the results together. The WDL-94 micro-sulfur analyzer developed by the Southwest Chemical Engineering Research and Design Institute uses a back-flushing technique, allowing for one injection per analysis, and the total sulfur content can be determined in three minutes. It is easy to operate, and it is used in petrochemical enterprises in Shandong Province; samples with high sulfur content can be analyzed by dilution.
Ultraviolet fluorescence method can achieve 0.2
This is what analytical instruments for fine chemicals are used for!
The correctness of the results is relative; all methods have their limitations in terms of application. In fact, I believe that the most classic methods are also the most accurate. Aren’t all advancements in instrumental analysis based on data evaluations obtained by comparing results with those from chemical analysis? Actually, people these days are lazy; they always assume that the instruments used are the most advanced. The principle behind microcoulombs is Faraday’s law of electrolysis, which states that the amount of electricity used in electrolysis is proportional to the amount of substance involved. Both ultraviolet fluorescence and X-rays originate from emission spectra; they involve the proportional absorption of light energy (quanta) based on the content of a substance, with the only difference being the frequency of the light energy. In principle, it still follows Beer’s law. The only difficulty in quantifying gases is that their volume can fill any space, and it is influenced by temperature and pressure; moreover, since gases are invisible and intangible, it seems difficult to measure them. However, once proper sampling and injection methods are used, along with easy ways to determine their volume and mass, there are no issues left.