HPLC
Not what you're looking for?
In HPLC, how often should I need to run standard with samples? Why? If the retention time is changed with real samples compared to standard, how can I determine if the peak with changed retention time is samples are actually compounds A and B?
Purchase this Solution
Solution Summary
This solution offers details discussion and step-wise logical analysis of some major concerns related to HPLC, along with citation of some resourceful references.
Solution Preview
A.
In HPLC analysis, standards are run and their retention times are noted down in order to calibrate the instrument. Essentially this means running the calibration standards at the beginning of the sequence and at the end, and makes the assumption that any changes occurred in a linear manner during the sequence. The data system then changes the calibration incrementally from the beginning to the end, and applies this to the results.
Drift of peaks due to change in retention time is a major issue in HPLC. To identify the causes (shown in blue below) and remedies of these problems needs step-wise logical analysis:
(1) A new column may require several priming injections for the constituents of a sample to irreversibly bind to the most active surface silanol species - each injection being exposed to successively fewer silanol groups and hence producing a slightly different (typically shorter) retention time. To reduce the requirement for priming injections one should choose a high quality stationary phase, which uses Type B (type II) silica and which has a low metal ion content. To speed up the column 'equilibration' process, one should consider injecting a sample at 10x the usual concentration in order to quickly cover the surface silanol ...
Education
- BSc (Hons),
- MSc,
- PhD,
Recent Feedback
- "Thankyou for the feedback. I have a few question though; With the first statistic about cost below... “According to Sigma-Aldrich catalog, cost of 1L octane is AUD $ 392.00, whereas the cost of 1L ethanol is AUD $196.00. Moreover, if ethanol is obtained from sugar industry as a by-product, it may cost even less. Source of oxygen is ambient atmosphere, so it costs nothing. So ethanol is much cheaper than petrol, in fact it is half-priced: AUD $ (392-196) = $ 196.” I didn't think it made sense because the cost of petrol per litre is normally a dollar something or even less than a dollar not a couple of hundred of dollars. For example, a statistic that I found in america was: "U.S. ethanol production costs are about $1.20 per gallon of ethanol, or $1.82 per gallon on a gasoline-equivalent basis." However, I was wondering whether you could find an Australian statistic. Also, you mentioned that H20 is not a greenhouse gas. However, in the combustion equations it is actually carbon dioxide and water vapour which are produced and they are both greenhouse gases. Finally, how do I calculate the energy efficiency of ethanol and petrol? "
- "Thank you!"
- "Didnt really answer my questions but gave me a start at least."
- "Once again this is tremendous help I can't thank you enough for not only working the problem but explaining in detail how and why!! KR"
- "Awesome thank you so much for the help!!!"
Purchase this Solution
Free BrainMass Quizzes
Functional groups in Organic Chemistry
You will be tested on the names of functional groups in Organic Chemistry. It is very important to know the functional groups to understand Organic reactions.
Match Elements with their Symbols
Elements are provided: choose the matching one- or two-letter symbol for each element.
General Chemistry - Classification of Matter
This test will assess your knowledge on the classification of matter which includes elements, compounds and mixtures.
Thermochemistry
The quiz helps in revising basic concepts about thermochemistry.