Fig. 5.

(a) The pyomelanin was prepared from bacteria fed with increased tyrosine. Also synthetic pyomelanin was prepared from a solution of 20 mmol/L HGA at pH 10 and left for 7 days at 20°C. The samples were added to 10–15 kDa dialyser pack and dialysed against pure water for 24 h with two changes of the dialysate. The samples were then dried before analysis using a Micromass M@LDI™ linear MALDI-TOF -MS, with conditions MCP voltage 1,850, laser power 85, pulse voltage 1,500 and nitrogen UV laser 337 nM; (a) the m/z spectrum observed after straight injection into the MS with no modifier present, (b) MALDI MS with matrix modifier alpha cyanocinnamic acid and (c) MALDI MS with matrix modifier dihydroxy benzoic acid. For scans (b) and (c), top is the control matrix alone, middle synthetic and bottom bacterial pyomelanin. The pyomelanin and scans were provided by Dr CE Turick Savannah River National Laboratory, South Carolina USA