MESO-Rx
Anabolic Steroids
Are all the insults really needed CBS? I've seen you post some really good thoughtful perspectives. Couldn't you ask the same thing without them and be just as effective if not more? Do you really think someone is going to take you seriously or give two shits about a good question anymore?
Okay! Carry on.. My mistake
While I certainly applaud the effort many will not even read that prolonged verbiage mate. I liken molecular polarity to that of a magnet, and have found greater success in maintaining the interest of the audience by using my own words.Has the oxandrolone standard been out of production long, or do you believe there is a possibility that it could still be found given enough cyber sleuthing?
This is the best I could come up with vis-a-vis polarity, specifically within the context of HPLC. It was taken from a manufacturer's website, and seems to be a fairly accessible, high level overview:
Separations Based on Polarity
A molecule’s structure, activity, and physicochemical characteristics are determined by the arrangement of its constituent atoms and the bonds between them. Within a molecule, a specific arrangement of certain atoms that is responsible for special properties and predictable chemical reactions is called a functional group. This structure often determines whether the molecule is polar or non-polar. Organic molecules are sorted into classes according to the principal functional group(s) each contains. Using a separation mode based on polarity, the relative chromatographic retention of different kinds of molecules is largely determined by the nature and location of these functional groups. As shown in Figure P, classes of molecules can be ordered by their relative retention into a range or spectrum of chromatographic polarity from highly polar to highly non-polar.
Figure P: Chromatographic Polarity Spectrum by Analyte Functional Group
Water [a small molecule with a high dipole moment] is a polar compound. Benzene [an aromatic hydrocarbon] is a non-polar compound. Molecules with similar chromatographic polarity tend to be attracted to each other; those with dissimilar polarity exhibit much weaker attraction, if any, and may even repel one another. This becomes the basis for chromatographic separation modes based on polarity.
Another way to think of this is by the familiar analogy: oil [non-polar] and water [polar] don’t mix. Unlike in magnetism where opposite poles attract each other, chromatographic separations based on polarity depend upon the stronger attraction between likes and the weaker attraction between opposites. Remember, “Like attracts like” in polarity-based chromatography.
Figure Q: Proper Combination of Mobile and Stationary Phases Effects Separation Based on Polarity
To design a chromatographic separation system [see Figure Q], we create competition for the various compounds contained in the sample by choosing a mobile phase and a stationary phase with different polarities. Then, compounds in the sample that are similar in polarity to the stationary phase [column packing material] will be delayed because they are more strongly attracted to the particles. Compounds whose polarity is similar to that of the mobile phase will be preferentially attracted to it and move faster.
In this way, based upon differences in the relative attraction of each compound for each phase, a separation is created by changing the speeds of the analytes.
Figures R-1, R-2, and R-3 display typical chromatographic polarity ranges for mobile phases, stationary phases, and sample analytes, respectively. Let’s consider each in turn to see how a chromatographer chooses the appropriate phases to develop the attraction competition needed to achieve a polarity-based HPLC separation.
Figure R-1: Mobile Phase Chromatographic Polarity Spectrum
A scale, such as that shown in Figure R-1, upon which some common solvents are placed in order of relative chromatographic polarity is called an eluotropic series. Mobile phase molecules that compete effectively with analyte molecules for the attractive stationary phase sites displace these analytes, causing them to move faster through the column [weakly retained]. Water is at the polar end of mobile-phase-solvent scale, while hexane, an aliphatic hydrocarbon, is at the non-polar end. In between, single solvents, as well as miscible-solvent mixtures [blended in proportions appropriate to meet specific separation requirements], can be placed in order of elution strength. Which end of the scale represents the ‘strongest’ mobile phase depends upon the nature of the stationary phase surface where the competition for the analyte molecules occurs.
Figure R-2: Stationary Phase Particle Chromatographic Polarity Spectrum
Silica has an active, hydrophilic [water-loving] surface containing acidic silanol [silicon-containing analog of alcohol] functional groups. Consequently, it falls at the polar end of the stationary-phase scale shown in Figure R-2. The activity or polarity of the silica surface may be modified selectively by chemically bonding to it less polar functional groups [bonded phase]. Examples shown here include, in order of decreasing polarity, cyanopropylsilyl- [CN], n-octylsilyl- [C8], and n-octadecylsilyl- [C18, ODS] moieties on silica. The latter is a hydrophobic [water-hating], very non-polar packing.
Figure R-3: Compound/Analyte Chromatographic Polarity Spectrum
Figure R-3 repeats the chromatographic polarity spectrum of our sample [shown in Figure P]. After considering the polarity of both phases, then, for a given stationary phase, a chromatographer must choose a mobile phase in which the analytes of interest are retained, but not so strongly that they cannot be eluted. Among solvents of similar strength, the chromatographer considers which phase combination may best exploit the more subtle differences in analyte polarity and solubility to maximize the selectivity of the chromatographic system. Like attracts like, but, as you probably can imagine from the discussion so far, creating a separation based upon polarity involves knowledge of the sample and experience with various kinds of analytes and retention modes. To summarize, the chromatographer will choose the best combination of a mobile phase and particle stationary phase with appropriately opposite polarities. Then, as the sample analytes move through the column, the rule like attracts like will determine which analytes slow down and which proceed at a faster speed.
Normal-Phase HPLC
In his separations of plant extracts, Tswett was successful using a polar stationary phase [chalk in a glass column; see Figure A] with a much less polar [non-polar] mobile phase. This classical mode of chromatography became known as normal phase.
Figure S-1: Normal-Phase Chromatography
Figure S-1 represents a normal-phase chromatographic separation of our three-dye test mixture. The stationary phase is polar and retains the polar yellow dye most strongly. The relatively non-polar blue dye is won in the retention competition by the mobile phase, a non-polar solvent, and elutes quickly. Since the blue dye is most like the mobile phase [both are non-polar], it moves faster. It is typical for normal-phase chromatography on silica that the mobile phase is 100% organic; no water is used.
(http://www.waters.com/waters/en_US/HPLC-Separation-Modes/nav.htm?cid=10049076&locale=en_US)
-B
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