Sol−Gel Germania Triblock Polymer Coatings of Exceptional pH Stability in Capillary Microextraction Online-Coupled to High-Performance Liquid Chromatography

Abstract

For the first time, a germania-based sol-gel coating was used in capillary microextraction (CME) in combination with high-performance liquid chromatography (HPLC). A hydroxy-terminated triblock copolymer, poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide), was covalently bonded into a sol-gel germania matrix in the course of its creation from an alkoxide precursor via hydrolytic polycondensation reactions. A thin layer of this in situ-created sol-gel hybrid material was covalently anchored to the inner walls of a 0.25 mm i.d. fused silica capillary to produce a sol-gel germania triblock polymeric sorbent in the form of a highly stable surface coating. Such a coating served as an effective extracting phase for the preconcentration of a wide range of polar and nonpolar analytes (e.g., alcohols, amines, ketones, phenols, and polycyclic aromatic hydrocarbons) with nanomolar and picomolar detection limits. Most significantly, the sol-gel germania triblock polymer coating demonstrated impressive resistance to extreme pH conditions, surviving 5 days of continuous exposure to 1.0 M HCl (pH approximately 0.0) or 1.0 M NaOH (pH approximately 14.0), practically without any changes in performance. This shows the suitability of sol-gel germania hybrid organic-inorganic hybrid materials for use as sorbents or stationary phases under extreme pH conditions, often needed in a variety of separation and sample preparation techniques and applications, including ion chromatography, hydrophobic interaction chromatography, proteomics, HPLC with electrochemical detection, isoelectric focusing, and extraction of acidic and basic analytes.

High-temperature solvent stability of sol–gel germania triblock polymer coatings in capillary microextraction on-line coupled to high-performance liquid chromatography

“…During this process, the sol-gel active terminal hydroxyl groups of the triblock polymer condensed into the growing sol-gel network forming an organic-inorganic hybrid sol-gel material. This chemical bonding was verified through FTIR data presented our previous report [21]. Portions of the sol-gel germania triblock polymer network growing in the vicinity of the fused silica capillary inner surface simultaneously condensed with silanol groups on the inner walls of the capillary to produce a surfacebonded sol-gel germania triblock polymer coating that served as the extracting phase when such a capillary was used in CME.…”

“…), nuts and Rheodyne ferrules. Gravity-fed extraction was conducted as described in our previous work [21]. In this study, we also used an HPLC pump driven extraction system ( Fig.…”

“…The chemical anchoring of sol-gel coatings to the fiber [1] or inner walls of the fused silica capillary [3] is responsible for their enhanced thermal and solvent stability [1]. Sol-gel CME coatings have been effectively coupled with GC [3,[5][6][7][8][9][10], capillary electrophoresis (CE) [11,12], inductively coupled plasma mass spectrometry [13,14], and high-performance liquid chromatography (HPLC) [15][16][17][18][19][20][21]. Sol-gel coated microextraction capillaries can easily be hyphenated on-line with HPLC [15][16][17][18][19][20][21], without the need to use complex desorption devices which are required to couple fiber SPME to HPLC [22].…”

“…Recently, Segro et al [21] reported the creation of the first germania-based sol-gel coating for use in capillary microextraction on-line hyphenated with high-performance liquid chromatography. These coatings were prepared using the germania-based sol-gel precursor, tetra-n-butoxygermane, and the hydroxy-terminated triblock polymer, poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide).…”

“…These coatings were capable of extracting a variety of analytes from different chemical classes, ranging from polar to nonpolar, with low picomolar to low nanomolar detection limits. Most significantly, the sol-gel germania triblock polymer coatings demonstrated impressive pH stability, surviving long-term (5 days) continuous exposure to 1.0 M HCl (pH ≈ 0) and 1.0 M NaOH (pH ≈ 14) [21].…”