Spectrophotometer muaj ib tug yuav ua ntau lub wavelengths ntawm hom teeb ci, mus txog hauv spectroscopic ntaus ntawv, uas ua rau muaj kev wavelength txog hom teeb ci, lub teeb los ntawm kev kuaj mus kuaj, ib feem ntawm lub teeb yog absorbed, xam cov qauv absorbance tus nqi, uas yuav txia mus ua tus concentration ntawm cov pawg. Kuaj absorbance nqi proportional rau lub concentration ntawm cov pawg.
Monochromatic lub teeb tawg los ntawm cov khoom ntawd raws li kuaj cov kua, cov absorbed los ntawm cov khoom thiab cov concentration ntawm cov khoom thiab tus thickness ntawm txheej ua kua yog proportional rau kom kev kho qhov muag, qhov zoo yog raws li nram no:
Ib = - lg (I/i). = - lgT = kLc
Hom: A, rau lub absorbance.
I. rau xwm siv lub teeb;
Kuv kom tau cov kev siv lub teeb;
T rau cov transmittance uas muaj ntaub ntawv;
K rau kom tus hniav puas haum coefficient;
L yog cais txoj kev kho qhov muag kev, namely, lub sab ntev ntawm WIC colorimetric;
C yog qhov concentration ntawm qhov siv tshuaj;
Khoom haum xim wavelength rauv, thiab cov coj haum coefficient yog qhov khoom ntawd constants. Thaum twg ib yam khoom uas ntshiab si paub nyob tej lub caij no muaj nyob rau tom qab qhov haum coefficient kev kuaj mus kuaj hauv qhov mob tib yam li dej, ntsuas cov absorbance, tau ua payment ntawm cov hom tshuaj ntsuam kuaj hauv cov ntsiab lus ntawm cov ntaub. Lub teeb haum thaum pom lub teeb thaj av ntawd, ntxiv rau tej yam khoom nws tus kheej ntau tsis nqus tab sis txis chromogenic reagent rau tej yam mob los yog tom qab ua ua nws cov xim ntsuas dua, ces nws kuj hu ua colorimetric tsom. Ua chromogenic yam rau xim qhov tob ntawd ntau, thaum cov neeg pluag thiab nquag siv monochromatic taws purity kev ntsuas, yog li kev txiav txim rau daim ntawv thov uas txheem siv tshuaj thiab siv yam khoom uas tib lub sijhawm.