Separation of transition and heavy metals using stationary phase gradients and thin layer chromatography

Abstract

Stationary phase gradients for chelation thin layer chromatography (TLC) have been investigated as a tool to separate a mixture of metal ions. The gradient stationary phases were prepared using controlled rate infusion (CRI) from precursors containing mono-, bi-, and tri-dentate ligands, specifically 3-aminopropyltriethoxysilane, N-[3-(trimethoxysilyl)propyl] ethylenediamine, and N-[3-(trimethoxysilyl)propyl] diethylenetriamine. The presence and the extent of gradient formation were confirmed using N1s X-ray photoelectron spectroscopy (XPS). XPS results showed that the degree of modification was dependent on the aminosilane precursor, its concentration, and the rate of infusion. The separation of four transition and heavy metals (Co(2+), Pb(2+), Cu(2+), and Fe(3+)) on gradient and uniformly modified plates was compared using a mobile phase containing a stronger chelating agent, ethylenediaminetetraacetic acid (EDTA). The retention of the metal ions was manipulated by varying the surface concentration of the chelating ligands. The order of retention on unmodified plates and on plates modified with a monodentate ligand was Fe(3+)>Cu(2+)∼Pb(2+)∼Co(2+), while the order of retention on plates modified with bi- and tri-dentate ligands was Fe(3+)>Cu(2+)>Pb(2+)∼Co(2+). Fe(3+) and Cu(2+) were much more sensitive to the concentration of chelating ligand on the surface (displaying lower Rf values with increasing ligand concentration) than Pb(2+) and Co(2+). Complete separation was achieved using a high concentration of the tridentate ligand coupled with a longer time for modification, yielding a retention order of Fe(3+)>Cu(2+)>Co(2+)>Pb(2+).

Interband transitions in closed-shell vacancy containing graphene quantum dots complexed with heavy metals

“…During the last decades, extensive research efforts have mostly been focused on development/improvement of effective ''bulky'' detection methods (chromatography, mass spectrometry, etc. ), [13][14][15] design of sensitive materials and devices (electrodes, hybrid structures, field emission transistors, and Schottky diodes), [16][17][18][19][20][21][22][23][24][25] and fabrication of potent adsorbents (filters, and membranes). [26][27][28][29][30][31][32][33][34][35] Considering the drawbacks of the traditional ''bulky'' time-consuming techniques, numerous research groups, nowadays, investigate graphene-family materials (graphene quantum dots, reduced graphene oxide, epitaxial graphene, etc.)…”

Recent applications of chemometrics in one‐ and two‐dimensional chromatography

“…In some cases, the required selectivity for a sample cannot be obtained by using a homogeneous column. For this reason, stationary-phase gradients were recently introduced [201][202][203]. However, prediction of retention times on these columns, and, therefore, separation optimization, are problematic.…”

In situ silanization for continuous stationary phase gradients on particle packed LC columns

“…Constructive CRI (i.e., adding ligands to a substrate) is a costefficient and straightforward method to produce multicomponent chemical gradients on silica supports, by exposing one end of a substrate longer than another to a hydrolyzed organosilane solution. [17][18][19][20][21]31,32 Adaption of constructive CRI to a particle packed column that is suitable for LC, however, has not been attainable until now. Compared to planar substrates and monolithic columns, the time-dependent modication of a traditional LC packed column in situ is much more challenging, not only because of the increased back pressure required for infusion into a packed column, but also because of the high surface area and microporosity of the silica powder.…”

“…This is a method developed by the Collinson group to form chemical gradients on planar substrates such as silicon wafers and thin layer chromatography plates using silane chemistry. [17][18][19][20][21] Our research on the use of this methodology to form a stationary phase gradient on a particle packed column in situ rst began with the optimization of the type and the concentration of silane, along with the infusion parameters. The nalized method involved infusing a phenylbutyltrimethoxysilane (PBTMOS) solution through a 5 cm long packed column containing particles that are 5 mm in diameter (d p ) to generate a phenyl-butyl gradient stationary phase.…”