‘ChemWell for Wine’

Technical Bulletin

Bulletin 8-2014 (2):  "Residual Water droplets"

‘After ChemWell washes wells, I see small (5 or 10uL) droplets of DI water (i.e. incompletely aspirated Rinse Water) in a few wells.  Will these affect my results?’



Residual droplets in the washed CW Reaction wells are completely normal and won’t affect subsequent ABS result.  In fact, this ChemWell's Vertical Reading advantage - residual rinse water (or addition of diluent) does not affect the ABS readings. 


Intuitively this is clear: compare the color of a rose wine vs. one diluted 10% with water. You will see this color difference looking from the side of the glass (fixed light path) but not looking down through the glass (variable light path, longer when water is added.)  CW lamps are above the reaction wells, the photometer below; any remaining rinse water in the wells dilutes the light-absorbing substance but also increases the vertical light pathlength to the same degree - so the absorbance is not affected.  


The Lambert-Beer Law is the underlying science:

Abs = log (I(0)/I) = e X c X l.
I(0) = Incident light intensity, I = Transmitted light intensity, e = molar absorption coefficient (L/mole-cm),

c = concentration of light-absorbing substance (moles/L), l = light pathlength (cm).

This equation mathematically confirms your intuition (and the rose color experiment.) 

You may find a nice explanation of the Lambert-Beer Law if you still have your old Biochemistry 101 textbook; alternatively, view our on-line explanation.  Consider the example on page 3; we have programmed ChemWell for Wine to pipette yellow Selft Test solutions into CW Cuvettes in two separate conditions and compare the Absorbance values obtained:


  1. Solution #1, a diluted yellow dye (i.e. a mixture of PNP and Blanking Solution used in our Self Test), is delivered to multiple wells in varying volumes, producing variable vertical light paths and therefore variable Absorbance values.


  1. 10 uL of Solution #2, the concentrated yellow PNP dye (used in our Self Test), is delivered to each well, followed by variable volumes of Diluent. In this case:
    1. The Absorbance values are constant, each well has the same quantity of PNP dye.  Because the light path (vertical distance through the well) varies, the variable volume of Diluent does NOT affect ABS values
    2. Note: If one removes the reaction wells from the ChemWell and views color from the side, the wells with more diluent are seen as lighter yellow, this constant (horizontal) light path reveals lower ABS.  Likewise, when using a (fixed pathlength) spectrophotometer cuvette, adding diluent reduces absorbance of the solution.


Unitech Scientific

Technical Service Department