Hi All,
I wonder that if I have dilute a very small volume of substance A in a very large volume of substance B. For example dilution 1:20000 of an antibody in TBST. Mixing it well by vortex or whatever for 2 mins. Then aliquots or divides the solution- equally volume into two tubes. How can be so sure that these two tubes have almost or nearly equal amount of antibody? Is it possible that one of these might not contain an antibody at all or contain only very small amount.
Thank you and Cheerio,
Generally yes a diluted aliquot will contain the corresponding quantities determined by calculation. The assumption is that the statistical distribution of a truly dissolved or suspended solute in a solvent is constant to more significant figures than most other errors.
This assumption is true unless the molecular concentration is infinitesimally low e.g. 100 molecules per litre, but even then It would be almost impossible to split the solution in half and have 100 molecules in one test tube and 0 molecules in the other.
This sampling error can be calculated to a fairly significant precision. As a thought experiment, think of a jar containing a trillion red coloured balls and a million yellow coloured balls. If you were to pick a ball at random from the jar and place half of all those balls into a new jar then it will contain extremely close to half a million yellow coloured balls and half a trillion red coloured balls.
Avogadro's number is 6 x 10^23. which is absolutely huge it means that your sample size in molecules will always be high enough that you can ignore the sampling error. Any significant difference you get in quantity will be due to a physical error.
One important point to consider is solubility of substance A in solvent/substance B. In high solubility situations, then you can reliably count on the dilution (within errors introduced by measurment and addition). If there are limited solubilities, then you can end up with clustering/clumping of component A which would yield errors in concentration.This is especially true when dealing with materials that have polar and non-polar qualities.
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