Thin layer chromatography

Introduction

Thinlayerchromatographyismostcommonlyusedasadsorptionchromatography.Commonlyusedadsorbentsaresilicagel,alumina,etc.Thin-layerchromatographyisthesameasotherchromatographicmethods.Inadditiontoadsorption,itcanalsoperformchromatographywithmechanismssuchasdistribution,ionexchange,andmolecularexclusion.Theoperationofionexchangers,gels,etc.isbasicallythesameastheadsorptionmethod.

Process

Boardmaking

Whenlayingthin-layerboards,thebaseboardisrequiredtobecleanandflat,anditcanbemadebydryorwetlaying.Nowadays,thewetmethodiscommonlyusedtomaketheboard,thatis,theadsorbentandthebinder(suchascalcinedgypsum)aremixedinacertainproportion,andanappropriateamountofwaterisaddedtomixevenly.Thehomogenateisslowlymovedacrossthebaseboardwithaspreader,placedtodry,andthenappropriatelyItcanbeusedafterbakingactivation.Ifnoadhesiveandwaterareadded,andtheadsorbentisevenlyspreadintoathinlayer,itisadrymethod.Nowadays,therearevariouskindsofpreparedthin-layerboardsonthemarket,collectivelyreferredtoasprefabricatedboards.

Expand

Therearemanyways,theabovemethodisthemostcommonlyused.Placethethin-layerboardverticallyorobliquely,addthespreadingsolventtothelowerpart,andmakeitmovefrombottomtotop.Thedownwardruleistousefilterpapertoguidethesolventtotheupperendofthethinlayersothatitflowsfromtoptobottom.Whenunfoldinginparallel,laytheplateflat,andthesolventissuckeduptotheendwherethesampleisspottedonthethinlayerplateforunfolding.Whenusingacircularthin-layerplate,pointthesamplenearthecenterofthecircletomakethesolventmovefromthecenterofthecircletothecircumferentialdirection,whichiscalledannularexpansionorradialexpansion;pointthesampleonthecircumferentialpositionsothatthesolventmovesfromthecircletothecenterofthecircle.Heartexpansion,suitablefortheseparationofcomponentswithlargef-values.Scrapeofftheadsorbentnearthesamplepoint,sothatthesolventcanonlyspreadforwardthroughthenarrowpartnearthesamplepoint,sothesolventfrontedgeisarc-shapedexpansionmethod,alsocalledradialexpansion,whichismoredifficulttoseparateThecomponentsmaybemoreeffective.

Afterunfoldingonce,takeoutthethin-layerboardtovolatilizethesolvent,andthenusethesamesolventorchangetoanothersolventtounfolditagaininthisdirection.Pointthesampleatonecornerofthesquarethin-layerplate,firstunfolditinonedirection,thenrotatetheplate90°,andthenunfolditintheotherdirectionfortwo-wayunfolding.Bothmultipleexpansionsandtwo-wayexpansionscanenhancetheseparationeffect.

Features

Easytooperate,simpleequipment,nospecialequipmentisrequiredexceptforthedensitometer,theseparationeffectisbetter,thetimeisshort,andmanysamplescanbeseparatedononeplateatthesametime.Inadditiontolow-boilingsubstances,variousinorganicandorganiccompoundscanbeseparated.

Applicationanddevelopment

Widelyusedinpetroleum,chemical,pharmaceutical,biochemicalandotheraspects.Thesampledosageisgenerallyafewtoseveralhundredsofmicrograms,whichisamorepracticalandeffectivemicro-separationanalysismethod.Thismethodcanalsobeusedtoseparateandpreparealargeramountofsamples,thatis,usealargerandthickerthin-layerplatetodotthesamplesolutionintoastripatthestartingpoint,sothatthemilligramsamplecanbeseparated.