A. Gago-martinez et al., Effect of pH on the oxidation of paralytic shellfish poisoning toxins for analysis by liquid chromatography, J CHROMAT A, 905(1-2), 2001, pp. 351-357
The effect of pH on the oxidation of individual PSP toxins using both perio
date and peroxide oxidations was studied. It was found that the optimum pH
for individual toxins varied considerably. For periodate oxidations, pH 8.3
produced the maximum yield of fluorescent products for neosaxitoxin and GT
X1/GTX4 while the non-hydroxylated toxins (saxitoxin, GTX2/GTX3, decarbamoy
l saxitoxin, GTX5) showed optimum pHs from about pH 10-11.5. Neosaxitoxin a
nd GTX1/ GTX4 did not produce significant fluorescent oxidation products wi
th peroxide oxidation at any of the pHs studied (pH 8.2-12.8). The non-hydr
oxylated toxins all showed optimum pHs above pH 12 with peroxide oxidation.
Yields of fluorescent products of these toxins decreased substantially at
pHs below pH 12. Neosaxitoxin and GTX1/GTX4 each produced three product pea
ks at pH 8.2 with periodate oxidation. There was no pH where these toxins p
roduced predominantly a single oxidation product. Decarbamoyl saxitoxin alw
ays produced two oxidation products with both oxidation reactions at the pH
s studied. However, the relative yields of the products changed with pH. At
low pH the second eluting product predominated, while at higher pH values
the first eluting product predominated. This pattern was observed for both
oxidation reactions. The other non-hydroxylated toxins produced mainly sing
le unique products with both oxidation reactions over the pH range studied.
No single pH was found optimum for the oxidation of both hydroxylated and
non-hydroxylated toxins without a significant compromise in yield of oxidat
ion products. This has implications for the post column oxidation liquid ch
romatographic methods, since small changes in pH of the post column oxidant
can both positively and negatively affect the yields of oxidation products
of toxin mixtures leading to increased error in the subsequent quantitatio
n of these compounds. (C) 2001 Elsevier Science B.V. All rights reserved.