Why my HPLC ODS column does not give reproducible peaks?
471672
Depends on the method that you are using, and/or the age of the column. If the column is older than one year, or has more than 1000 hours of run time, it may be suspect. \n\nWith regards to the sample you are running, make sure that what you are running is compatible with an ODS column. Some chemistries will react with the silane groups and become permanently attached to the column. Also, make sure there are no matrix issues that could be obscuring your results. The sample might have to be washed or cleaned to remove/reduce matrix effects.\n\nWith the method you are running, make sure that you are properly cleaning the column after each run because some things may be retained on the column and not eluting.  You may have to run a stronger cleaning solvent to clean the column and then re-equilibrate with your running solvent.  Also, make sure that your running solvent stays constant and is not changing due to evaporation or any other factors. \n\nObviously to give reproducible results the methods that you use must remain as constant as possible. Check each of your method parameters to make sure nothing is changing. \n\nHope this helps without going into a treatise on HPLC theory and methodology.
663462
There is NO way for anyone to answer that without knowing the relative concentrations of active ingredients in both the pills and the liquid.  There are too many different sizes of pills and strengths of liquids to make anything resembling an accurate guess.
990083
You don't give us which lab you are doing, so results would be hard to find..  For general information, do a good web search with the name of what you distilled.  I don't think you will find everything you want, but there is a large number of websites on the general subject.
1162796
HPLC user’s guide: http://kerouac.pharm.uky.edu/ASRG/HPLC/hplcmytry.html\n\nGas Chromatography (GS) http://en.wikipedia.org/wiki/Gas_Chromatography . Here you may also find (at the bottom of the article), external links to the other analytical methods.
74804
I moved from the city to the country here in S.C. and had to put a well down. Look for DHEC. Should be one close. Its a State agency and they gave me a jar with instructions for  a sample. They tested it and the cost was free. Good luck>
650140
You need to start your values at "0", i.e. for your source data, you need to add 0 as the first entry for both Minutes and Grams (I know nothing about Chemistry but I'm trying to make sense..). That way, when you use the Chart Wizard, the starting point will be 0,0 on your chart. \n\nI think this answers your question, however if my answer sounds as vague to you as it does to me, I've uploaded an image for you to have a look at. Go to: http://i4.tinypic.com/10e0w00.png\n\nGood luck and I hope that helps.
304287
This is called Base line correction.\nYour solvent may be having some absorption, or the impurities in it may be having some absorption..so to measure your compunds absorption exactly, you need to take the solvent (n whcih you are going to dissolve your compound later) and do this base line correction.\nIn a way you are telling instruments "NOT TO WORRY ABOUT THESE ABSORPTIONS"\n\nThats it\nYou got it?
135532
You can either look it up or determine it experimentally.\nI cant get much more specific without additional details.
158796
I assume you know what osmosis is.\nIt would be nice to end up with enough results to plot a graph (LINE graph) so you will need at least four (more is better) solutions of different concentrations. Sucrose solution is usually used.\nUse a BIG potato so that all your samples are as similar as possible.\nThe easiest way to get uniform samples is to cut cylinders with a cork borer, then cut into 5mm disks.\nPut 10 discs into each solution.\nWeigh 10 discs before they are put in, then CAREFULLY blot them dry and reweigh them next day.\nCalculate the change in mass per gram of potato (you could expect some to gain, some to stay the same and some to lose so you will get some negative values).\nPlot a line graph of 'change in mass per gram of potato' AGAINST 'concentration of solution'.\nNow you must consider what the graph show you.
97726
I know of no way to determine this without a counter. Go to link below for quality counter that is hidden from viewer's site. FREE and gives you great reporting.
310596
The first question is what are you trying to accomplish. The amount of material will direct you to one method.  Also, the polarity of your material will dictate the method you will employ.  Silica gel columns are relatively cheap and will work for most things but not all. They also tend to be more useful for larger scale chromatography in terms of speed and convenience. Reverse phase columns are expensive and require expensive equipment and detectors.  However, they will separate material more efficiently than a silica gel column but the scale will be smaller.  If your material is chiral then you need chiral columns which are very expensive and also need special equipment like reverse phase equipment.  Lastly, there are additional method like gas chromatography, ion exchange, capillary electrophoresis and other less commonly used methods which all have some utility based on the first statement.
1027922
Typically, all GC and HPLC columns are made of a silicaceous material, which is then coated on the interior surfaces with a variety of materials to modify their absorptive/attractive qualities.  A C8 column has a variety of 8-carbon alkyl groups (could be n-octyl, or perhaps methyl-heptyl, etc) bonded to the silica surface; a C18 column has 18-carbon alkyl groups bonded; a C4 column has butyl-groups.\n\nThe differing nature of the treatments alters the attractive qualities of the column walls, thereby altering the retention times of the various analytes.  If you have an idea what your analytes are, you can then chose the specific column that will do a better job of separating them.
883855
The samples must be homogenously ground to enable the solvent to fully soak into the sample and extract the compound you want in question. Also there is a question of statical averages so a uniformed powder sample is the best for this process. If the sample is lumply or too big the solvent can't fully soak into it and wherefor not all of your compound in question is extracted by the process (Then the solvent fills up the soxhlet thumbie (sp)). If this happens you will get a incorrect value then you come to do the maths in determinating the amoult of the coumpound in question.
814606
pH samples need to be analyzed immeditely for regulatory purposes.  There is no holding time.  They must be test ASAP.
406869
I think you miscopied the third item.  You have copied one of the first helf cells, not given a reaction.
450305
The question was presented as an example of something puzzling - you have a substance - tartaric acid if i remember that is not optically active and then you have the same substance (but made as a result of microbial activity) that has identical properties, the only difference is that it is optically active - nobody then knew why\n\nhe let the optically inactive solution  crystalize, looked really close and well and compared - then noticed that the crystals differ - are like a miror image, he manually sorted them out and WOW the 2 solutions were optically active - the same degree but oposite direction (if you understand me, i do not know what this is called in english). then he assume that the microbes can do the sorting in their body. He spent his lifetime looking in microscopes or experimenting with unbelievable patience while enyybody else would have given up long time ago, thats why he made so many breakthroughs
220155
Are you asking for an explnation for the spectral proprties  or doy ou want the actual spectral report? either way go here....http://orgchem.colorado.edu/hndbksupport/irtutor/estersir.html