SixLiquidChromatographyDetectorsThatAnalyticalResearchersShouldKnow
PharmaceuticalanalysisistheapplicationofanalyticalchemistryinpharmacyItisa "methodscience"fortheresearchanddevelopmentofdrugqualitycontrol.Itmainly useschemical,physical-chemical,orbiochemicalmethodsandtechniquestostudy chemicalstructuresthathavebeenclarified.
UV-VisAbsorptionDetector
Ultraviolet-visibledetector(UVD)isoneofthemostwidelyuseddetectorsinHPLC, andalmostallliquidchromatographsareequippedwiththisdetectorUVDis characterizedbyhighsensitivity,widelinearrange,lownoise,andissuitablefor gradientelution.Thedetectionlimitforstronglyabsorbingsubstancescanreach1ng, andthesamplewillnotbedestroyedafterdetection.Itcanbeusedforpreparation andcanbeusedinserieswithanydetector.Theworkingprincipleandstructureof theUV-visibledetectoraresimilartothegeneralspectrophotometer,anditis actuallyaUV-visiblephotometerequippedwithamobileground.
UltravioletabsorptiondetectorandPhotodiodearraydetector(PDAD)arethetwo mostcommonlyusedultraviolet-visibledetectors
Fluorescencedetector
Fluorescencedetector(FD)isahighlysensitiveandselectivedetectorthatcandetect compoundsthatproducefluorescence.Somenon-fluorescentsubstancescanbe chemicallyderivatizedtogeneratefluorescentderivatives,whichcanthenbe detectedbyfluorescence.
Itsminimumdetectionconcentrationcanreach0.1ng/ml,whichissuitablefortrace analysis.Undernormalcircumstances,thesensitivityoffluorescencedetectorsis about2ordersofmagnitudehigherthanthatofultravioletdetectors,butitslinear rangeisnotaswideasthatofultravioletdetectors.
Inrecentyears,laser-inducedfluorescencedetectorsproducedbyusinglaserlightas thelightsourceoffluorescencedetectorshavegreatlyenhancedthesignal-to-noise ratiooffluorescencedetection,sotheyhavehighsensitivityandarewidelyusedin traceandultra-traceanalysis
DifferentialRefractiveIndexDetector
Thedifferentialrefractiveindexdetector(RID)isaconcentration-typeuniversal detectorthatrespondstoallsolutes,andsomecomponentsthatcannotbedetected byselectivedetectors,suchaspolymers,sugars,andfats,canbedetectedwitha differentialdetector.Differentialdetectorsarebasedonthecontinuous
measurementofthechangeinrefractiveindexbetweenasampleflowpathanda referenceflowpathtodeterminesamplecontent.
Whenlightpassesfromonemediumtoanother,refractionoccursduetothe differenceintherefractiveindexofthetwosubstancesAslongastherefractive indexofthesamplecomponentisdifferentfromthatofthemobilephase,itcanbe detectedThegreaterthedifferencebetweenthetwo,thehigherthesensitivityIna certainconcentrationrange,theoutputofthedetectorisproportionaltothesolute concentration
Electrochemicaldetector
Electrochemicaldetectors(ED)mainlyincludeamperometric,polarographic, coulombic,potential,conductometricandotherdetectors,whichareselective detectorsandcandetectcompoundswithelectroactivity.Atpresent,ithasbeen widelyusedinthedeterminationofvariousinorganicandorganicanionsandcations, metabolitesofbiologicaltissuesandbodyfluids,foodadditives,environmental pollutants,biochemicalproducts,pesticidesandmedicinesAmongthem, conductivitydetectorsaremostwidelyusedinionchromatography.
Chemiluminescencedetector
Chemiluminescencedetector(CD)isafastandsensitivenewdetectordevelopedin recentyears,knownforitsadvantagesoflowpriceandwidelinearrangeThe principleisthatcertainsubstancesundergochemicalreactionsatroomtemperature togeneratereactionintermediatesorreactionproductsinanexcitedstate,and whentheyreturntothegroundstatefromtheexcitedstate,theyemitphotons.
Sincetheenergyoftheexcitedstateofmattercomesfromchemicalreactions,itis calledchemiluminescence.Whentheseparatedcomponentsareelutedfromthe chromatographiccolumn,theyareimmediatelymixedwithanappropriate chemiluminescentreagenttocauseachemicalreactionthatcausestheluminescent substancetoemitradiation,theintensityofwhichisproportionaltothe concentrationofthesubstance.
Thisdetectordoesnotrequirealightsourceoracomplicatedopticalsystem.Aslong asthereisaconstantflowpump,thechemiluminescentreagentispumpedintothe mixeratacertainflowrate,sothatitcanbemixedwiththecolumneffluentquickly andevenlytoproducechemiluminescence,andthenusethephotomultipliertubeto converttheopticalsignalintoanelectricalsignal.Theminimumdetectionamountof thisdetectorcanreach10-12g
EvaporativeLightScatteringDetector
EvaporativeLight-scatteringDetector(ELSD)candetectcompoundswithout chromophores,suchascarbohydrates,lipids,polymers,underivatizedfattyacidsand aminoacids,surfactants,drugs,andcandetectunknowncompoundsintheabsence ofstandardsandunknowncompoundstructuralparameters.
Theuniquedetectionprincipleoftheevaporativelightscatteringdetectoristhatthe columneluentisfirstatomizedtoformanaerosol,thenthesolventisevaporatedin aheateddrifttube,andfinallytheremainingnon-volatilesoluteparticlesare detectedinthelightscatteringdetectioncell
CDFormulationisequippedwithanexperiencedqualityresearchteamand cutting-edgetechnologytoprovidevariouspharmaceuticaltestingservices,suchas thegeneralphysicalpropertyanalysisofrawmaterialsanddrugs,parameter characterization,biologicaltesting,impuritydetection,andstabilitystudies.