Amperometric Titration Largely Overestimates Chloride Concentrations in Chloroplast Extracts

D eterm ination of chloride con ten ts in aqueously isolated chloroplasts from spinach by am ­ perom etric titration indicated chloride concentrations of 60 to 100 m m ol l_l (based on a chloro­ plast volume of 25 (a.1 m g^1 chlorophyll). H ow ever, when analyzed by anion chrom atography, chloride contents in chloroplasts w ere much lower (1 — 8 mmol I 1). In leaf extracts chloride concentra tions ob tained with both m ethods w ere ra ther sim ilar. Boiling o f chloroplast extracts prior to chloride titra tion reduced indicated chloride contents by a factor of th ree o r four, but did not change results ob tained with anion chrom atography. It is concluded that chloroplasts contain large am ounts o f silver com plexing agents giving rise to a drastic overestim a­ tion of chloroplast chloride concentra tions when m easured by am perom etric titration . Boiling and centrifugation of extracts apparen tly p recip itates these com pounds only insufficiently.