HPLC Retention Behavior of Poly-Aromatic-Hydrocarbons on Aminopropyl Silica Gels Modified with Cu(II)- and Ni(II)-Phthalocyanine Derivatives in Non-polar Eluent

Abstract

were purchased from Aldrich, U.S.A. Phthalocyanine (H 2 -PC) was obtained from Tokyo Kasei, Japan. As a supports, Develosil NH 2 -5 ® (hereinafter, referred to as "Dev", Nomura Kagaku, Japan) which is a spherical aminopropyl silica gels (particle size, 5 mm; specific surface area, 350 m 2 /g; average pore size, 120 Å) was used. As an eluent, n-hexane for HPLC (Nacalai Tesque, Japan) was mainly used, and as a solvent for packing M-PCS D , slurry solvent A Conc. (Chemco Scientific, Japan) was used. The commercially available PYE ® column and NPE ® (nitro-phenylethyl silica gels) column (Nacalai Tesque, Japan) were used for comparison to elucidate the underlying separation mechanism of the M-PCS D column. M-PCS D ColumnsMetal-phthalocyanine tetrasulfonyl chloride (MPCSCl: MϭH 2 , Ni 2ϩ and Cu 2ϩ , see Fig. 1) was synthesized from H 2 -PC, Cu-PC and Ni-PC as described by Nadler et al.17) The resultant Ni-PCSCl (5.6 mg), Cu-PCSCl (5.6 mg) or H 2 -PCSCl (5.3 mg) was each dissolved in dioxane (150 ml), following the addition of Dev (1.5 g), and was refluxed for 2 h. After standing to cool, M-PCS D was separated by filtration, and washed with methanol (100 ml), dried thoroughly in vacuo over diphosphorous pentoxide. The M-PCS D column was then prepared by packing the obtained M-PCS D into a stainless-steel column (f4.6ϫ150 mm) for HPLC by a conventional slurry packing method. Throughout the process, the filtrate and the like were clear and colorless, and the absorption spectra thereof were free from characteristic absorption band(s) of M-PCSCls or M-PCSs. From these evidences, it was concluded that M-PCS was completely immobilized on silica gels. The amount of M-PCS immobilized was also estimated from the absorption spectrum of the initial M-PCS solution in dioxane.

HPLC Retention Behaviors of p-Electron Rich Compounds on Ni2+- and Cu2+-Phthalocyanine Derivatives Bound to Silica Gels in Polar Eluents

“…As we previously reported, 12 anthrathene derivatives having a substituent(s) show similar k values, and cannot be separated in a non-polar eluent. We therefore investigated the retention behavior of anthrathene derivatives on Cu-PCSD and Ni-PCSD in a polar eluent, i.e., 80% or 90% methanol.…”

“…4. Considering that the k values on the Cu-PCSD column showed a linear correlation with those on the PYE column lacking a central metal in n-hexane, 12 the above results indicated that the π-π electron interaction is dominant in 80% methanol.…”

“…As we previously reported, Ni-and Cu-PCSD columns show different HPLC retention properties in a non-polar eluent, such as nhexane. 12 However, in a polar eluent, a π-π electron interaction related to the hydration energy (solvation energy) possibly occurs between the column and a simple PAH, which unlikely occurs in a non-polar eluent. To investigate the effect of the central-metal on the possible π-π electron interaction, we compared the retention factors (k) of simple PAHs on the Cuand Ni-PCSD columns in 80% methanol.…”

“…ANALYTICAL SCIENCES JULY 2006, VOL. 22 columns in n-hexane, 12 Ni-PCS exerts a π-d interaction in 80% methanol as well as in n-hexane. The k values in a polar eluent are smaller than those in a non-polar eluent, demonstrating that the π-d interaction is weaker in a polar eluent.…”