Chromatography a Superiority Formula

Written by Aram Hayrapetyan


"All flows, all changes". Heraclides

"It's not difficult to know, it is difficult to get familiar". Skovoroda The theory of gas chromatography, presented byrepparttar equation of Van Deemter,

(1) shows that for each chromatographic separation there exists an optimal flow rate above and below whichrepparttar 127668 column efficiency is reduced.

In practice,repparttar 127669 linear speed ofrepparttar 127670 sample zone moved byrepparttar 127671 carrier gas, is changed continuously and increases as it approachesrepparttar 127672 outlet, which results in a non-effective use of a part ofrepparttar 127673 column.

In this case equation (1) characterizesrepparttar 127674 optimal separation process only in that section ofrepparttar 127675 chromatographic column through whichrepparttar 127676 sample passes at an optional speed.

In equation (1) are constant values and isrepparttar 127677 speed ofrepparttar 127678 moving zone ofrepparttar 127679 sample which changes continuously in time. Thus equation (1) getsrepparttar 127680 following form:

(2) where isrepparttar 127681 speed ofrepparttar 127682 sample at a distance fromrepparttar 127683 beginning ofrepparttar 127684 column and changes - increases - towardrepparttar 127685 outlet. This shows that HETP is not always optimal in all sections ofrepparttar 127686 chromatographic column. Let berepparttar 127687 length ofrepparttar 127688 chromatographic column,repparttar 127689 pressure atrepparttar 127690 inlet ofrepparttar 127691 column andrepparttar 127692 pressure atrepparttar 127693 outlet ofrepparttar 127694 column,repparttar 127695 distance of a point onrepparttar 127696 chromatographic column from its inlet. It is evident that pressure at point onrepparttar 127697 column can be determined fromrepparttar 127698 correlation

The flow rate at any point onrepparttar 127699 chromatographic column depends on pressure at that point, as well as onrepparttar 127700 inlet pressure andrepparttar 127701 outlet pressure ofrepparttar 127702 column. Butrepparttar 127703 pressure at any point onrepparttar 127704 column depends onrepparttar 127705 inlet pressure andrepparttar 127706 outlet pressure ofrepparttar 127707 chromatographic column and onrepparttar 127708 distance fromrepparttar 127709 column inlet. Thusrepparttar 127710 flow rate at any point onrepparttar 127711 column in case of fixed physical parameters ofrepparttar 127712 chromatographic column can be considered as a function of pressure at this point and atrepparttar 127713 ends and ofrepparttar 127714 distance of this point fromrepparttar 127715 column inlet;

Consequentlyrepparttar 127716 whole process inrepparttar 127717 chromatographic column is characterized by a multiple of equations (3).

When atrepparttar 127718 inlet and outlet ofrepparttar 127719 columnrepparttar 127720 pressure is kept constant, each section ofrepparttar 127721 chromatographic column, through whichrepparttar 127722 sample zone moves, is characterized by its equation from multiple (3).

Howeverrepparttar 127723 linear speed ofrepparttar 127724 sample zone moving withrepparttar 127725 carrier-gas can be kept constant by programmingrepparttar 127726 pressure gradient movement alongrepparttar 127727 column in time, realizingrepparttar 127728 function: pressure - location - time by keeping constantrepparttar 127729 pressure difference ∆ p atrepparttar 127730 ends ofrepparttar 127731 chromatographic column duringrepparttar 127732 whole cycle ofrepparttar 127733 analysis (Russia Patent "Chromatograph of A. S. Hayrapetyan").

The sample travels throughrepparttar 127734 chromatographic column in time

where isrepparttar 127735 length ofrepparttar 127736 chromatographic column andrepparttar 127737 optimal speed ofrepparttar 127738 sample zone.

The pressure atrepparttar 127739 inlet and outlet ofrepparttar 127740 chromatographic column, undergoing a change at equal intervals of time, is expressed by

where - sample injection time, and - elution time.

We mark by

the sections ofrepparttar 127741 chromatographic column travelled byrepparttar 127742 sample zone with an optimal velocity ofrepparttar 127743 carrier-gas atrepparttar 127744 corresponding moments of time,

A spring called: Drop of water

Written by K.A.Cassimally


Do you know what happens when a drop of water hits a non-absorbent surface? Yeah youíre right (if you donít haverepparttar answer, please re-readrepparttar 127667 title of this column),repparttar 127668 drop bounces upwards.

A French scientific team fromrepparttar 127669 Collēge de France have studiedrepparttar 127670 scene carefully with a camera that took 40000 images per second. Here arerepparttar 127671 results: At first, when it hitsrepparttar 127672 surface,repparttar 127673 drop flattens. Then, it bounces up due torepparttar 127674 movement energy it had when falling down. The drop will continue going upwards eventually takingrepparttar 127675 shape of a needle. Afterwards,repparttar 127676 drop falls upon itself, into itself. It thus takesrepparttar 127677 shape of a pancake (again) but this time,repparttar 127678 drop is in midair.

This phenomenon is different to a drop falling on other surfaces as in this case,repparttar 127679 drop crashes onrepparttar 127680 surface leaving only a small quantity ofrepparttar 127681 water to bounce up. Physicists have also found out thatrepparttar 127682 actual speed of a drop influences its deformation but notrepparttar 127683 time taken for it to get in contact withrepparttar 127684 surface. This actually depends uponrepparttar 127685 mass ofrepparttar 127686 drop.

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