Analysis of unknown impurities
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Recently, small white particles were found in the products; they can be removed, but they are very small – even the larger impurities are only half the size of a sesame seed. What method should I use to determine what this impurity is? Is there any expert in analysis who can give some guidance? I dissolved the substance in toluene, which indicates that it is an organic compound, not an inorganic one. This post was last edited by Chengzheng on 2009-2-25 14:56.]
A few minor suggestions: 1. Please ask your analysts to dissolve it in methanol, and then conduct analysis using the same methods they employ for analyzing your raw materials or finished products. Make sure the conditions remain unchanged; with that, you can obtain preliminary boiling point data. 2. Have the personnel in charge of the manufacturing process conduct a process analysis, search the internet for possible side reactions, and look up the boiling point characteristics of relevant impurities. Then ask the procurement department to acquire these suspected impurities for qualitative analysis. 3. If there are distinct peaks in the gas chromatogram, things are simple – there are analysis instrument platforms available in various provinces on the internet; you can request their assistance, though this will incur costs. 4. If no peaks appear in the gas chromatogram, then the only option is to use a liquid chromatography-mass spectrometry system, but this is more expensive, and since the spectrum database for liquid chromatography isn’t as comprehensive, the chances of success are lower compared to using gas chromatography-mass spectrometry. Good luck to you
It is best to first discuss the matter with the process engineers to determine what impurities might be introduced or generated, and then select an appropriate qualitative analysis method based on the characteristics of those impurities.
Generally speaking, in gas chromatography, peaks appear based on the boiling point; the higher the boiling point, the longer it takes for a peak to appear. This allows one to determine the boiling point of an unknown substance using the sandwich principle. By then comparing it with known impurities, the process of screening can be simplified through elimination. Of course, using gas chromatography-mass spectrometry or liquid chromatography-mass spectrometry is the most convenient approach
Identify relevant side reactions to narrow down the scope, and then determine new analysis methods based on the properties of the side reaction products.
How much sample is required for gas chromatography? I now doubt 2,4-dichlorobenzoic acid; do you think infrared spectroscopy can confirm it?
Qualitatively speaking, it’s about one gram. If you have doubts about certain components, it’s recommended that you purchase a small amount; performing qualitative analysis is quite simple. Quantitative analysis is a bit more complicated, but qualitative analysis is the first step – once that is done, the workload for quantitative analysis decreases
Infrared spectroscopy requires a high level of purity in the sample; I don’t think it’s a very good tool for qualitative analysis, as it seems that the sample is a mixture
Was your friend’s problem solved? CAS: 50-84-0 Molecular formula: C7H4Cl2O2 Molecular weight: 191.01 Boiling point: 200°C Melting point: 160–164°C Chinese name: 2,4-Dichlorobenzoic acid English names: 2,4-dichloro-Benzoic acid, 2,4-Dichlorobenzoic acid, 2,4-dichloro-benzoic aci, Benzoic acid,2,4-dichloro- Description of properties: White to pale yellow needle-shaped crystals or powder. Melting point 160°C, readily sublimes, no boiling point. Soluble in ethanol, ether, benzene, propylene, chloroform, and 5% sodium hydroxide solution; insoluble in water and heptane. Production method: 2,4-Diaminotoluene undergoes a diazotization reaction in the presence of sulfuric acid and sodium nitrite; subsequently, substitution takes place in the presence of copper(I) chloride to yield 2,4-dichlorotoluene. This compound is then oxidized with potassium permanganate to give the potassium salt of 2,4-dichlorobenzoic acid, which is further acidified with hydrochloric acid to produce 2,4-dichlorobenzoic acid. The reaction products are crystallized, washed, and dried to obtain the final product. Uses: Can be used as a dye, fungicide, and intermediate for pharmaceuticals. Used in the production of the antimalarial drug artemisinine hydrochloride and the mercury-free diuretic furosemide. Quality specifications: Appearance: white crystals; Purity: ≥99%; Melting point: 162–164°C; Moisture content: ≤0.5%. Is this useful to you? Note that the text mentions easy sublimation; it is recommended that you compare it. Last edited in this post by lifanwang on 2009-2-12 at 19:59.]
Since it’s an organic unknown, running a mass spectrometry analysis should allow us to figure out what it is, right? If it is a mixture, then chromatography-mass spectrometry or liquid chromatography-mass spectrometry should be used.
After reviewing the original poster’s question, the following steps can be tried for analysis: Since it has been determined that it is an organic substance, and the possible impurities can be inferred from the reaction materials, gas chromatography or liquid chromatography can be used first to conduct a preliminary analysis to determine whether it is a mixture, as well as to identify the conditions necessary for separating the mixture； Then, gas chromatography-mass spectrometry or liquid chromatography-mass spectrometry analysis is used to identify the various components.
I’m considering QCMS, but I’m worried about the small sample size. The initial plan is to start with infrared first, after all, fewer samples are needed for infrared testing. Who knows where in Tianjin one can get infrared services? Please provide a contact address.
Compared to chromatography, a significant amount of sample is required for infrared analysis; the amount needed varies depending on the instrument used. Moreover, it is difficult to analyze infrared spectra, especially when the sample is a mixture. It is advisable to avoid using infrared analysis in such cases.
It seems that your impurities are a mixture, and infrared spectroscopy simply cannot determine this. With such a small sample size, purification is not possible; it is more feasible to use chromatography and compare it with standard samples of the possible substances.
I think you should start by examining the manufacturing process, compare it with previous batches produced, and figure out what caused the issue and how to prevent the same problem from occurring. Determining what the impurity is has no practical use.
It is crucial to identify the impurities; only by identifying them can we determine which step in the production process is problematic. Wait, school starts next week; I’ll go and ask for advice.
Start by examining the process to determine whether it will work. 1. First, analyze the possible side reactions from a process perspective. 2. Determine the properties of each by-product based on the side reactions, and check whether their appearance is the same as or similar to that of your impurities. 3. First, determine the range of impurities, and then proceed with qualitative analysis; this helps to avoid unnecessary detours.
I went to the university for an infrared test like that yesterday; the results will be available next week. I’m waiting! ! ! ! ! ! ! ! ! !
Can mass spectrometry analysis be used?
Based on your description, I think infrared can be used for this. When taking samples, try to include as little or no surrounding material containing unknown substances as possible. Then, drying is necessary, as infrared technology is sensitive to water. The amount of sample required isn’t large either; just a few dozen milligrams are sufficient for a test； Of course, you can also use a mass spectrometer or a chromatography-mass spectrometry instrument for this, but the cost will be very high ； Using chromatography directly for qualitative analysis is quite troublesome; the results obtained through chromatographic qualitative analysis are not accurate – they are rather imprecise. It is necessary to change the column, the detector, as well as other parameters related to chromatography.
It was created using infrared technology; KBr was ground and compressed into tablets. The components have been identified, and the testing costs are not high. Thank you all for your interest. I haven’t tried chromatography-mass spectrometry; it’s too expensive – 800 yuan per sample. However, I think the chromatography-mass spectrometry method should work. This post was last edited by Chengzheng on 2009-2-25 at 14:58.]