SILICA GEL MODIFICATION BY NICKEL(II) COMPLEXES WITH NITROGEN- AND OXYGEN-CONTAINING ORGANIC LIGANDS FOR GAS CHROMATOGRAPHY

Abstract

Gas chromatographic sorbents based on Siloсhrome S-80 adsorptively modified with 8-hydroxyquinolinate, 1-phenylazo-2-naphtholate and 2-nitroso-1-naphtholate of nickel(II) have been obtained. It has been established that the thermal stability (up to 170–350 °C) of chelate-containing sorbents is sufficient for carrying out gas chromatographic separations. The IR and Raman spectra of the obtained materials confirmed the success of the complexation processes in the synthesis of complex nickel(II) compounds and the retention of coordination bonds after the deposition of chelates on silica gel. The characteristics of the surface and the porous structure of the prepared sorbents are investigated. As a result of adsorptive modification of Silochrome S-80 with nickel(II) chelates, it’s specific surface area (84 m2/g) decreases by 12–32 m2/g along with a decrease in the average pore size, which indicates the fixation of modifiers at the edges of large pores. It was shown that modification of Silochrome S-80 with 8-hydroxyquinolinate, 1-phenylazo-2-naphtholate, 2-nitroso-1-naphtholate of nickel(II) has a significant effect on the chromatographic polarity and selectivity of sorbents. The presence of a polar nitroso-groups in the composition of nickel(II) 2-nitroso-1-naphtholate makes the metal center more accessible for donor-acceptor interactions with sorbates (pyridine, carbonyl compounds). Also, the nitroso-group is active in the formation of hydrogen bonds with alcohols, which complicates their elution at column temperatures below 170 °C. The greatest affinity to the homologous of arenes is shown by silochrome modified by a nickel(II) complex with the least bulky 8-hydroxyquinolinate ligands, which leads to an increase in the retention times of aromatic and polyaromatic compounds along with an increase of the sorbent selectivity. The possibility of practical application of a chromatographic column filled with Silochrome S-80 with deposited nickel(II) 8-hydroxyquinolinate for gas chromatographic (FID) separation of mixtures of polyaromatic compounds in the temperature programming mode is shown.