Clean cells with mild liquid detergent and/or diluted nitric acid (1% wt) by
dipping or filling the cell with solution and agitating for 3 to 4 minutes.
Diluted HCl (hydrochloric acid) or H2SO4 (sulfuric acid)
may also be used. When stronger cleaning is needed, try concentrated HCl mixed
into 50% isopropanol (rubbing alcohol). Rinse the cell several times with
distilled or deionized water and recalibrate before use.