| Author | Message | ||
     Nuno Matos (Nmatos) |
Dear All, Does anyone have experience with powders. I'm finding very hard to obtain reproductible results. I'm reading a static surface of the sample. I'm trying now to use a rotational device in order to increase sensibility. Can anyone give hints to deal with powders? Thanks | ||
| mpdc |
Can you give some more info? What kind of powders are you measuring? what do you mean with "reproducible"? Spectra? Predictions? classifications? Particle size has a big effect when measuring powders, but there are ways to compensate. Inhomogenity is another one. | ||
| Nuno Matos (Nmatos) |
I'm talking about a powder from a fermentation. I know about particle size (MSC, 2nd derivative). The thing is, for instance, by PCA, it's different two spectra from the same sample but measured in different days. | ||
| MPDC |
questions to ask: -is my sample stable? -does the humidity change? (look at 1900 nm) -is it homogenous? If you take the two raw spectra from the 2 days, and subtract them from each other, what do you see? Rotating the sample should solve most problems caused by inhomogenity. You can see how inhomogenous your samples are by measuring different spots in the same sample. Compare this variation to your day-to-day variation. You can test for sample stability by repeating your measurement after 2 hours, 4 hours etc. | ||
| Bruce H. Campbell (Campclan) |
Since you obtained spectra on two different days, you may have settling/compaction if you left the sample in the sample container. If you left the sample in the container, did you "refresh" the sample by taking another portion or removing it and then refilling the container? Bruce | ||
| Gabi Levin |
Dear Nuno, Let us start by clarifying a few questions: 1. Is the product of the fermentation a chemical that you have dried in a lyophilizer? 2. Is it a chemical that you have dried in a spray dryer? 3. Is it possible that the compound that's in your "same sample" is forming structural changes (different polymorphs) due to interaction with moisture in the air? 4. Is it possible that absorption of moisture from the air causes changes due to hydrogen bonding between molecules? If any of these are possible, then your sample may be simply changing and then the spectra two days later will definitely be different! To check what is the cause of the change please see if you could do the following: 1. Seal some powder in a "SURESEAL" bottle and allow to "equilibrate" for 24 hours. 2. Collect spectrum through the glass wall in diffuse reflectance and rotate the bottle twice and collect again. Average these spectra into one spectrum. 3. Allow the bottle 48 hours and repeat. 4. Now compare the spectra and see if there is any difference. If the product was dried in a lyophilizer, some times it takes time for the product to reach it's final crystalline form when exposed to moisture in the air. This can account for spectral changes with time. Spray dried products are more stable morphologically, so I would expect less changes there, but even this can be a false statement, depending on your compounds. Bottom line - know your chemistry, know your compounds, their behaviour under yor experimental set-up, under your processes, design experiments that will enable you to elucidate the different influences of different conditions on your spectra, then you would have meaningful information. Thanks, Gabi Levin | ||
| Nuno Matos (Nmatos) |
MPDC: The sample is stable. For the rest of your suggestions I will do that Bruce: The samples used for the two readings type were obtained from the same portion. Gabi: 1,2- This product is raw material for me so I don't know how is the drying process but not lyophilization 3- The sample is keeped in a closed recipient 4- Without being sure I don't think so Thank you all | ||
| Gabi Levin |
Dear Nuno, Thanks, 1. Raw material - supplied from an external source, or an internal division of your comany? Withour revealing critical commercial information, what type of material is it? Is it a protein, peptide? fatty acid? complex organic molecule with benzene rings, with carboxilyc groups, with amino groups? 2. Is it in crystalline form, or amorphous? 3. If the same sample, in a closed sealed vial is used to collect specrta every 24 hours, for 5 days or so, do you see a continuous change, or is it becoming same spectrum after some time? 4. What type of spectrometer are you using? Hope I can help, Gabi Levin Brimrose |