“…HPLC methods have been the main approach [9][10][11][12][13][14][15]. Other techniques reported are monolithic silica rod liquid chromatography [16], micellar liquid chromatography [17], capillary electrophoresis [1,18,19], titrimetry [20], spectrophotometry [21][22][23], diffuse reflectance spectroscopy [24] and chemiluminescence [25]. All of these methods need a pre-extraction step, usually solid-phase extraction (SPE), for clean-up of matrix complexity prior to quantitative analysis.…”