Coulombic sulfur and fluorescent sulfur

What kind of fluorescence method is used for the determination of sulfur by fluorescence? Also, what type of sample or what kind of oil it is. If it is the ultraviolet fluorescence method, please check the instrument settings and conditions, as well as the representativeness of the sample. If it is X-ray fluorescence method, please check the sulfate or sulfate ester content in the sample.

Was the same sample used for comparison? What is the applicable range for these two methods you are using? If the sample concentration falls outside this range, the detected results will generally have certain errors.

Coulombic sulfur should be used as the standard, as it has high sensitivity and a low detection limit, resulting in higher accuracy when analyzing samples with low concentrations

Reply to 4# liuyu682: The ultraviolet fluorescence method has higher sensitivity and can detect levels around 0.01 ppm. Your perspective is a bit outdated – not by very long, perhaps about 15 years.

Reply to 5# qugd: I think specific issues need to be analyzed on a case-by-case basis. The original poster asked about sample preparation, and the reproducibility is poor when using fluorescent sulfur and Coulomb sulfur for such purposes. This indicates that the laboratory in question has a Coulomb sulfur analyzer and a fluorescence sulfur analyzer; I believe both of these instruments are of domestic manufacture. As far as I know, the detection limit for fluorescence sulfur analyzers is generally 0.2 ppm, and when analyzing samples with low concentrations, the results tend to be on the high side. When using low-content samples of Cullen sulfur, the results are more accurate, though the human error is relatively large. And the detection limit you mentioned is 0.01 ppm, which is usually found in imported instruments. As far as I know, the elemental analyzers available in Jena can achieve a detection limit of 0.01 ppm for sulfur detection; (our laboratory uses the Multi 5000.) If the laboratory in question already has an instrument with such a low detection limit, then why would it need to purchase two flow meters? When I was in school, there were only 2 sulfur analyzers in the school laboratory: one of the Coulomb type and one of the fluorescence type. Generally, the Coulomb analyzer was used to measure low levels of sulfur, while the fluorescence analyzer was used for higher levels. Therefore, I believe that for samples with low sulfur content, the Coulomb method provides more accurate results. I wonder if you agree with my view?

I also think that the ultraviolet fluorescence method has higher sensitivity; it is specifically used for analyzing National Standard 3 diesel

Regardless of the instrument used for analysis, the results should not differ significantly; a difference of several times over in the case of ppm levels as you mentioned is indeed a problem. You need to calibrate the instrument. No matter what the instrument is or how high its sensitivity, it is necessary to create a standard curve (or recovery curve) after some time; this is done to determine the extent of deviation from the standards as well as to check the condition of the instrument. Here, for the Jena EA5000 units, it is required to prepare standard curves twice a month.

Such small gas samples should not be analyzed using fluorescence sulfur; the lower limit for determining fluorescence sulfur by standard methods is 1 PPm. In fact, the lower detection limits for fluorescence sulfur in China generally do not reach this value, as fluorescence sulfur in China is mainly used for testing refined oil, and the standard for refined oil is below 50 PPm. In China, it’s very difficult to separate fluorine sulfur at levels below 10 PPm; let alone when measuring gases at around 1 PPm – it’s simply not possible. The best method for analyzing such gases is Coulombic sulfur analysis. As long as care is taken to control the injection speed, data with very good repeatability can be obtained!