Unique On-Site Spinning Sampling of Highly Water-Soluble Organics Using Functionalized Monolithic Sorbents

Effect of crosslinker/porogen ratio on sponge-nested polymer monoliths for solid-phase extraction

Polymer monoliths can be polymerised within different molds, but limited options are available for the preparation of free-standing polymer monoliths for analytical sample preparation, and in particular, solid-phase extraction (SPE). Commercial melamine-formaldehyde sponges can be used as supports for the preparation of polymer monoliths, due its flexibility, giving various shapes to monoliths. Herein, the crosslinker/porogen ratio of highly porous sponge-nested divinylbenzene (DVB) polymer monoliths has been evaluated. Monoliths prepared using different crosslinker/porogen ratios were applied to the extraction of bisphenol F, bisphenol A, bisphenol AF, and bisphenol B. Monoliths containing 50 wt % DVB and 50 wt % porogens presented the highest recovery of bisphenols. Under the optimised conditions, the developed method showed a linear range between 2.5 µg L-1 and 150 µg L-1 for BPA and BPAF, and between 5 µg L-1 and 150 µg L-1 for BPB and BPF. The limits of detection (LOD, S/N = 3) and limits of quantification (LOQ, S/N = 10) ranged from 0.36 µg L-1 to 1.09 µg L-1, and from 1.20 µg L-1 to 3.65 µg L-1, respectively. The recoveries for spiked bisphenols (10 µg L-1) in tap water and water contained in a polycarbonate containers were between 82 % and 114 %.

Sponge-nested polymer monoliths: Versatile materials for the solid-phase extraction of bisphenols

Polymer monoliths are promising materials for sample preparation due to their high porosity, pH stability, and simple preparation. The use of melamine formaldehyde foams has been reported as an effective support to prepare highly robust silica and polymer monoliths. Herein, divinylbenzene monoliths based on a 50:50 (%, w/w) crosslinker/porogen ratio have been nested within a melamine-formaldehyde sponge, resulting in monoliths with a surface area higher than 400 m2 /g. The extraction performance of these monoliths was evaluated for the extraction of endocrine-disrupting bisphenols from aqueous solutions. We evaluated for the first time the versatility of sponge-nested polymer monoliths by comparing three different extraction modes (vortex mixing, magnetic stirring, and orbital shaking). Vortex mixing showed a comparable recovery of bisphenols (39%-81%) in a shorter extraction time (30 min, instead of 2 h). In addition, the robustness of the sponge-nested polymer monoliths was demonstrated for the first time by reshaping a larger monolithic cube (0.125 cm3 ) into four smaller pieces (4 × 0.03125 cm3 ) leading to a 16%-21% increase in extraction efficiency. This effect was attributed to an increase in the effective contact area with the sample, obtaining a higher analyte extraction capacity.

Sponge-nested polymer monolith sorptive extraction

Polymer monoliths are an alternative to traditional particle-packed supports used in solid-phase extraction because of their ease of preparation, high porosity, and pH stability. They often required the attachment of monoliths to a support, such as the internal walls of a column to enable their use for sample preparation. Applications of free-standing polymer monoliths are rarely found because of their limited mechanical stability. Herein, divinylbenzene monoliths were polymerised within a commercial melamine-formaldehyde sponge using different polymerisation times. The sponge-nested polymer monoliths are highly robust, and their size and shape can be easily adjusted for desired applications. The prepared sponge-nested polymer monoliths had surface areas in the range of 237 m² g^-1 to 369 m² g^-1. A melamine-formaldehyde sponge cut into 1 cm³ cubes were used to template the polymer monoliths. Miniaturized monoliths with a size of 0.125 cm³ were directly cut from the larger cubes without compromising the integrity of the porous monolith structure. The resulting nested monolith sorptive extraction (NMSE) supports were applied for the extraction of the endocrine disruptors bisphenol A, 4-tert-butylphenol, and 4-tert-octylphenol. The prepared sponge-nested monoliths are low-cost (40 monoliths/AU$). NMSE was carried out by the direct immersion of the monoliths in the aqueous standards/samples, requiring only an orbital shaker for the extraction procedure. Best performance was obtained for polymer monoliths polymerized for 6 h, enabling limits of detection of 5.6 to 6.5 µg L^-1 for the selected analysis using HPLC-UV.