Golden Rules:
Various conditions must be obeyed in order to achieve valid and reproducible spectra from Circular Dichroism spectrometers.  Not least:

        To avoid stray-light effects & poor S/N     

      0.4 < A < 1.4           


            where:    
A = Absorption (AU)

        For continuous scanning instruments   

     S.t / 60  <  B  <  W / 10          


             where:     S = scan speed (nm/min)
                           
 t = response (sec)
                            B = spectral bandwidth (nm)
                        
  W = width of spectral features (nm)



Thermal Effects:
Changing the temperature of a solution will affect a variety of things, which should be corrected for:

        Concentration, through expansion
      H2O ca. 2% from 0 to 100ºC, but can be 10-fold greater for organic solvents

        pH, through buffer temperature coefficient
      
e.g.  Tris varies ca. -2.8 pH units from 0 to 100ºC

 

Solvent Effects, the Lorentz Factor:
Due to its polarisable nature, a solvent will affect the Circular Dichroism spectrum observed irrespective of whether it directly interacts with or changes the molecules under study.  This effect is wavelength dependent and should be accounted for through the Lorentz Factor in studies with varying solvents:

        Lorentz Factor for CD     

       CDcorrected = CDobserved . 3/(nl2 + 2)

       where:     nl = refractive index of solvent at wavelength l nm

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