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Everything posted by Carvone

  1. What makes you think ribose is a stronger reducing agent than glucose? I am just curious, since in the 2,2'-bicinchoninic acid reducing end analysis, glucose gives a much higher response curve than ribose (Absorbance/concentration Slope). I recognize the only factor is not the reactivity to the 2,2'-bicinchoninate disodium salt at the reducing end but also the absorptivity of the new compound produced from the sugar and the 2,2'-bicinchoninate disodium salt that gives the blue color at 560 nm ABS. See std curve below. One possibility is since Ribose is a 5 carbon ring (aldopentose) while glucose is a 6 carbon ring (aldohexose), there is more pressure for ribose to open up (since ring bonds will be tighter stretched) thus making it more reactive at the reducing end.
  2. I would think that different cigarette brands would be best distinguished by their aroma compounds evolved during burning and subsequently run on GC/MS by either solvent extraction, SPME, SBSE or headspace analysis techniques, whereas the ash contents after burning based on ICP-OES or ICP-MS would best distinguish the growing/soil conditions of the tobacco and possibly the location where it was grown.
  3. A good method developer and analyst for GC/MS or LC/MS methods is more than just a technician who knows how to operate the instruments. It is kind of like saying "I should be able to sprint as fast as Usain Bolt, since all he is doing is running and we all know how to do that". Sorry, I do not mean to be insulting, but you really can't substitute a proficient analytical chemist for someone who has just learned to use the machine and be able to check for library matches. Experienced users can predict retention/elution times based on stereochemistry, Log P, boiling point (for GC) to verify compound identities. They will also instinctively know when something does not seem right, and know other ways to test for validation (FTIR, Raman, cNMR, etc.). In addition, they will know how to model/predict other variables such as response factors of different compounds to obtain more accurate quantity estimations. Not to mention, knowing the various sample preparation (SPE, SPME, SBSE, solvent extraction, SAFE) and derivatization techniques to allow less volatile compounds to be analyzed that may be required for extraction from different matrices due to different compound solubilities makes an experienced analytical chemist very valuable. I am not trying to say it is impossible for a non-experienced person to obtain these skills, but I would say you need a very strong interest to progress past this steep learning curve as well as a lot of time to develop this "analytical chemist" instinct. A used GC/MS system can be purchased for about $15,000 USD (an Agilent 5890 GC with an Agilent 5972 MS is considered an older but very reliable workhorse). The mass spectral database in learning will likely cost extra (up to $5000). LC/MS although much more versatile allowing higher MW compounds that can be solubilized in different mobile phases to be analyzed, it will cost more in capital expenses ($50,000+), require more maintenance, and peak resolution decreases overall allowing less compounds per run to be analyzed. My advice is partner-up with someone with this experience. It will benefit you in the short and long term. In this age of an ever-innovating and updating world, we cannot know everything so it is best to focus on what we are specialized in and very good at, and trust in those who know the other areas well that complement our skills. By sharing the wealth, it will ultimately bring in more wealth.
  4. Hello all, I have enjoyed the short time I have been on this forum reading all your questions and comments and learned a lot, having thought to myself "yes, I have had that same question as well!" I can see from the quality of the answers that there are some very smart people on here too I want to know if anyone who has some experience with polarimetry can direct me to some good resources for learning more about its use such as an internet site or a comprehensive book. I have found many websites that give the specific rotation for many of the sugars and other compunds such as organic acids and vitamins and some general information about the theory and how to calculate concentrations and the proportions of R and S enantiomers, but I wanted to delve deeper into the subject, such as how changing the wavelength of light used will affect the optical rotation and how this can be used to obtain more information, and how changing the solvent and perhaps derivatizing the analytes (eg. methylation) can both be used to obtain more information. More specifically, I have been reading up on the work of Fischer, Irvine and Haworth from the late 1800s and early 1900s and how they used polarimetry almost exclusively (combined with C, H and O elemental combustion analysis) to determine the structures of the different sugars and that for example maltose is a dissacharide of two glucose while sucrose consisted of one glucose and one fructose. And this was all before Mass Spec, NMR, FTIR, etc!! I know that there methodology involved methylated the different sugars before and after hydrolysis, and from this they deduced the ring structure of the sugars and the various linkages. I just have not been able to piece together yet how they accomplished this amazing feat over 100 years ago without the wealth of such advanced instruments we have at our disposal today. Any help in directing me towards this goal would be most appreciated! Thanks all!
  5. There is energy in electron-rich chemical bonds that can be oxidized. When chemical bonds break as in larger molecules breaking down into smaller ones such as gasoline (hydrocarbon chains) burning into CO2 and H2O or for humans the glucose consumed breaking down into CO2 and H2O, energy is provided for various functions to keep us living such as in synthesis of larger molecules from smaller ones (ie. proteins from amino acids).
  6. It totally depends on the reviewers and I would imagine on the publication. Reviewers are all likely professors (or their post-docs) who are very busy people, and GENERALLY will be given up to three months to review an article. They will always suggest edits or additions to the article, which means you will have to make their changes or address their criticisms if you disagree with their points (as sometimes the reviewer does not understand something very clearly and are criticizing based on not having fully grasped what you meant, which should make you think that maybe I need to make this area in the paper more clear). I would say overall a safe extimate for publication would be 3-9 months after original submission, and 9 months only if the paper needed majjor revisions.
  7. Cool. I actually work with iodine in my PhD project but I study starch and use iodine to help elucidate the structure of the starch based on forming a polyiodide complex in the long, straight, unbranched chains of amylose, which gives a vivid blue color, while the highly branched structure of amylopectin turns a red-violet color with iodine due to smaller polyiodide complexes that absorb light at lower wavelengths. I have wondered if this amazing characteristic of iodine has anything to do with its hypervalent nature. Care to share your thoughts on this? Interestingly, iodine is also used in the food industry to titrate different vegetable oils to give a degree of unsaturation due to mono and polyunsaturated fats.
  8. Thanks a lot, HI! Can I ask why you named yourself Hypervalent Iodine? Seems so strange to name yourself that. I guess it is a unique catalyst for selective reactions.
  9. Hello Organic Chemists, I wanted to ask your advice as to what would be the most efficient process to convert hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF). Thanks!!
  10. I remember reading an article a few years back. It's premise was basically that there was a real brain drain in the sciences, since everyone educated knows that it would mean pretty low money and working at the pressures of the corporate elite to continually try to improve on the alrady heavily-modified "better" mousetrap, and those with great grades (representative of those with high ambition and intelligence) tended to go into where access to the money was by studying corporate finance. Basically, it said those in the sciences were in it for true love of this profession and wanting to know about nature and its underlying laws, but would be destined for middle class working "slavery" to the Man (.... on Wall Street). But hey, it's a good thing that all the most intelligent geniuses in the world decided to go to Wall Street since their supreme wisdom, intelligence and foresight has led to an unparalleled period of economic prosperity and stability!!
  11. Trained anticipation of an event like Pavlov`s dog salivating at a bell associated with forthcoming food, only this time we shreek at the thought of a an upcoming, painfully-boring lecture.
  12. The asteroid belt has legalized clay marriage
  13. God is in the details..... of this argument. It keeps us connected and entertained believing there is a greater purpose than the purpose we create for ourselves.
  14. 5.6.6. Thiobarbituric acid (TBA) This is one of the most widely used tests for determining the extent of lipid oxidation. It measures the concentration of relatively polar secondary reaction products, i.e., aldehydes. The lipid to be analyzed is dissolved in a suitable non-polar solvent which is contained within a flask. An aqueous solution of TBA reagent is added to the flask and the sample is shaken, which causes the polar secondary products to be dissolved in it. After shaking the aqueous phase is separated from the non-polar solvent, placed in a test-tube, and heated for 20 minutes in boiling water, which produces a pink color. The intensity of this pink color is directly related to the concentration of TBA-reactive substances in the original sample, and is determined by measuring its absorbance at 540 nm using a UV-visible spectrophotometer. The principle source of color is the formation of a complex between TBA and malonaldehyde, although some other secondary reaction products can also react with the TBA reagent. For this reason, this test is now usually referred to as the thiobarbituric acid reactive substances (TBARS) method. TBARS is an example of a measurement of the increase in concentration of secondary reaction products. from: http://people.umass.edu/~mcclemen/581Lipids.html
  15. Sorry for the necromancy bump from 2004. Oops! Did not really look at the dates. I was just browsing through the site and this thread caught my interest.
  16. Perfect thanks greatly John! Truly amazing to see what was learned so long ago using only wet chemistry methods!
  17. Thanks John for your reply. Yes, I did know about how C, H, and O were calculated from CO2 and H2O based on mass to mole conversions. I am very interested to know how these early chemists did this so accurately, and what method they used to convert their organic matter to CO2 and H2O, and then how did they trap these two substances (water and a gas) and then weigh them out. For example, how do you weigh a gas back in 1890? Perhaps they trapped the CO2 in some sort of balloon-like material (eg. goat intestine), and then measured the volume by displacement and converted this to mass or moles, but I am only guessing. I hope there is someone out there that knows how this was done over 100 years ago to be able to figure out the molecular formula of compounds. For nitrogen, the Kjehdahl method was first used long before Dumas, and was developed by a chemist from the Carlsberg brewery named Kjehldahl (hey whaddya know!) in the 1880s in Denmark. The 3-minute Dumas method has now largely replaced the lengthy Kjehdahl method, which took half a day to perform and consumed quite a lot of chemicals, since it was based on acid digestion to liberate ammonia, trapping the ammonia in boric acid, followed by quantitative titration.
  18. Microsoft Excel answers it as #DIV/0!
  19. My favourite acid to use, and one of (if not THE) strongest organic acid is trifluoroacetic acid (TFA). It has a pKa of -0.25 and is 100,000 times stronger than normal acetic acid. http://www.org-chem.org/yuuki/acid/acid_en.html What makes it so amazing is that it is quite volatile with a boiling point of around 72 C, such that it can be used to digest polysaccharides or proteins into their respective sugar and amino acid units, respectively, and then it can be evapourated off quite easily with a simple nitrogen stream.
  20. Carbon dioxide is added to soft drinks because it has been shown to give a preferred sensory mouthfeel when consuming due to the tiny bubbles in the mouth creating the effervescence. If you create a membrane that allowed out the excess CO2 only, it would have to be at the nozzle of the bottle where once it was opened it purged out the CO2 and no liquid, and then a further step of removing the mesh would be required to allow pouring of the drink out of the bottle. I am not sure what membrane materials might allow this, but I know if there is a slow purge due to only opening a small orifice the CO2 gas will be preferentially purged out, such as what I will do when a bottle falls and only partially twist open the cap only slightly such that no liquid exits while the gas pressure does exit over a prolonged period of time. Perhaps instead of a membrane, think of a small orifice purge valve at the cap. Also, another solution is dramatically lowering the temperature of the soft drink although this is not an option if it is desired to consume the drink immediately. In solution, dissolved carbon dioxide turns to carbonic acid, and the dropping of the pop bottle causes nucleation of CO2 bubbles which decreases the solubility of the carbonic acid. By putting the bottle in the freezer for a few hours should alleviate the problem of the fizzing pop since at lower temperatures CO2 is more soluble in water as carbonic acid.
  21. If the two compounds both elute early then they have a low capacity factor (k'), and possibly slowing the flow rate may improve separation up to a calculated k' of about 20 and after that the peak widening you mention will be pretty severe. The best way and easiest way to improve selectivity of two closely eluting compounds is to change the chemistry of the system by (most easily) change mobile phase (eg. change from acetonitrile to tetrahydrofuran, add salts or adjust pH if compounds are pH sensitive). If that doesn't work, think of changing the stationary phase (eg. C18 column to amine column), and if that doesn't work perhaps there is a way to chemically derivatize one or both of the compounds to achieve better separation (eg. methylation, acetylation, etc.)
  22. Flavour mostly is due to the volatile aroma compounds, so you could steam distill the tobacco to extract the flavours (essential oils) and then dry the now flavour-depleted tobacco, or you could extract in ethanol (absolute/tincture) for the same effect and dry the tobacco. However, since the burning of the tobacco during the smoking process in the pipe creates new smaller MW volatile compounds due to pyrolysis (burning without oxygen) and incomplete combustion (burning with oxygen) of the polymers in the tobacco leaf, there will always be an inherent flavour from smoking your tobacco. I think, however, the the flavour compounds extracted from the tobacco leaves either using steam distillation or solvent extraction would be much more pleasant to your senses than the burnt notes generated during smoking, which tend to be harsh and acrid. Try putting dried grass or paper into your pipe and smoke it and you will know what I mean.
  23. Hi all, I currently study starch, and a side project I am working on is researching the early history of starch research, which inevitably involves a lot of research about simple sugars (glucose and maltose) from learning that starch degraded with acid to sugars and with enzymes to glucose, maltose and various MW dextrins. To be frank, I am quite amazed at what was known back 100 years ago considering the methods were very limited. Paper chromatography to separate the sugars was not available until 1943. Gas and liquid Chromatography came about 8 years later. Most of the experiments involved controlled degradation with enzymes or acids followed by analysis in a polarimeter (before & after methylation). However, another technique that is referenced a lot as early as the 1890s (that I have found) is the elemental composition (eg. % carbon, % oxygen and % hydrogen), which could be related to the molecular composition of glucose, maltose, etc. This was based on calculating the amount of CO2 and H2O I am guessing that was combusted from the original samples. However, nowhere could I find how the early carbohydrate chemists measured this so accurately, and I am very interested in this early technique. If someone knows how they accomplished this experiment with such great precision without such instruments as ICP-OES, I would really appreciate being educated about this. Thank you. Carvone
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