Capillary electrophoresis of pterin derivatives responsible for the warning coloration of Heteroptera

A new capillary electrophoretic (CE) method has been developed for analysis of 10 selected derivatives of pterin that can occur in the integument (cuticle) of true bugs (Insecta: Hemiptera: Heteroptera), specifically L-sepiapterin, 7,8-dihydroxanthopterin, 6-biopterin, D-neopterin, pterin, isoxanthopterin, leucopterin, xanthopterin, erythropterin and pterin-6-carboxylic acid. Pterin derivatives are responsible for the characteristic warning coloration of some Heteroptera and other insects, signaling noxiousness or unpalatability and are used to discourage potential predators from attacking. Regression analysis defining the parameters significantly affecting CE separation was used to optimize the system (the background electrolyte (BGE) composition, pH value and applied voltage). The optimized separation conditions were as follows: BGE with composition 2 mmol L(-1) the disodium salt of ethylendiamintetraacetic acid, 100 mmol L(-1) tris(hydroxymethyl)aminomethane and 100 mmol L(-1) boric acid, pH 9.0, applied voltage 20 kV and UV detection at 250 nm. Under these conditions, all the 10 studied derivatives of pterin were baseline separated within 22 min. The optimized method was validated from the viewpoint of linearity (R(2)≥0.9980), accuracy (relative error ≤7.90%), precision (for repeatability RSD≤6.65%), detection limit (LOD in the range 0.04-0.99 μg mL(-1)) and limit of quantitation (LOQ in the range 0.13-3.30 μg mL(-1)). The developed method was used for identification and determination of the contents of pterin derivatives in adults of four species of Heteroptera (Eurydema ornata cream color morph, Scantius aegyptius, Pyrrhocoris apterus and Corizus hyoscyami) and their distribution in the individual species was determined.