Tetrabutylammonium phosphate

Deoxyribonucleic acid sodium salt from salmon tests (Sigma-Aldrich, Darmstadt, Germany) and phosphate buffered saline tablets (PBS, Sigma-Aldrich, Darmstadt, Germany) were directly used as supplied. All aqueous solutions were prepared with ultra-pure water obtained from a Mili-Q Water system (Milipore Corp. Bedford, MA, USA). Interferents for the selectivity studies were L-cysteine (Cys, 97%, Sigma-Aldrich), DL-Homocystein (Hcy, 95%, Sigma-Aldrich), L-Glutathione reduced (GSH, 98%, Sigma-Aldrich), sodium azide (N₃⁻, 99.5%, Sigma-Aldrich), sodium sulphate (SO₄²⁻, ≥99%, Sigma-Aldrich), sodium thiosulfate (S₂O₃²⁻, ≥99.99%, Merck, Darmstadt, Germany), tetrabutylammonium iodine (I⁻, 98%, Sigma-Aldrich), tetrabutylammonium cyanide (CN⁻, 95%, Sigma-Aldrich), and tetrabutylammonium phosphate (PO₃⁻, 99%, Sigma-Aldrich).

Analytical reagent-grade hydrochloric acid 37%, nitric acid 65%, ortho-phosphoric acid 85%, glacial acetic acid, periodic acid, sodium hydroxide, sodium dihydrogen phosphate; HPLC-grade methanol and acetonitrile were from Panreac Quimica S.A. (Barcelona, Spain). Trichloroacetic acid, tetrabutyl ammonium phosphate, ammonium hydroxide 28–30%, 2-mercaptoethanol (2-ME), and heptane sulfonate were purchased from Sigma-Aldrich (Madrid, Spain).
The certified standards provided by Cifga S.A. (Lugo, Spain) were: saxitoxin (STX), neosaxitoxin (NEO), decarbamoyl-saxitoxin (dcSTX), gonyautoxins 1 and 4 (GTX1,4), gonyautoxin 5 (GTX5), gonyautoxins 2 and 3 (GTX2,3), decarbamoyl-gonyautoxins 2 and 3 (dcGTX2,3), and N-sulfocarbamoyl-gonyautoxins 2 and 3 (C1 and C2).