A spectrum is recorded at wavelengths between of 260 nm and 320 nm immediately
after preparation of the test solutions (1 min) and after 180 min of
storage. The change of absorption is calculated as the difference of the absorption
values at 305 nm. UV absorption is measured with a Perkin Elmer
Lambda 12 spectrophotometer at a scan speed of 60 nm/min with 1 cm
quartz cells. For details on the HPLC investigations see Riedel and Leopold
(2004). Briefly, a reversed phase HPLC method with UV detection is employed
and chromatograms are recorded at a wavelength of 305 nm.