Evaluation of Titanium and Titanium Oxides as Chemo-affinity Sorbents for the Selective Enrichment of Organic Phosphates

Abstract

Titanium (Ti) and TiO, Ti₂O₃, Ti₃O₅ and TiO_1.98 as well as TiO₂ have been evaluated as chemo-affinity sorbents for the selective enrichment of organic phosphates. A column-switching high-performance liquid chromatography (HPLC) system, constructed with a precolumn (4.6 mm i.d. × 10 mm) packed with the titanium sorbents, an anion-exchange analytical column and a UV detector (215 nm) was used. When an aqueous 0.015% trifluoroacetic acid (TFA) was used as a sample-loading solution, O-phospho-L-tyrosine (P-Tyr), phenyl phosphate and phenylphosphonic acid were adsorbed onto all of the titanium sorbents with recoveries of 60.9–102.9%. Some acidic compounds other than phosphates, such as benzenedicarboxylic acid (BDA) isomers, were also adsorbed onto all of the titanium sorbents. To improve the selectivity to organic phosphates, various sample-loading solutions were examined using a Ti precolumn, two phosphorylated peptides [Ile-Ser(p)-Val-Arg (PP1) and Gln-Ile-Ser(p)-Val-Arg (PP2)], P-Tyr, BDA isomers and diglutamic acid (Glu-Glu) as test compounds. Among the sample-loading solutions tested, such as TFA, HClO₄, organic acids, boric acid and NaCl, the use of 100 mM NaCl in 10 mM boric acid was found to be effective. The recoveries of PP1, PP2 and P-Tyr were 73.0, 88.3 and 71.5%, respectively, whereas those of Glu-Glu and BDAs were suppressed to only below 10%.