Donald F. Hagen

Membrane approach to solid-phase extractions

A novel material for separations has been developed in which efficient chromatographic particles are enmeshed in a network of PTFE fibrils to form a strong, porous sheet or “membrane”. The membrane can have a variety of sorptive or reactive properties, which are determined by the characteristics of the particulate chosen. The membranes, in the form of 47- or 25-mm disks, are used with standard filtration equipment. The use of hydrophobic octyl- and octadecyl-bonded silica particulates for reversed-phase extractions of environmental pollutants from an aqueous matrix, replacing conventional liquid-liquid extraction (LLE) is described. The water sample is filtered through the disk and adsorbed organic species are eluted from the disk with a small volume of an appropriate solvent for subsequent chromatographic separation. The technique is rapid, less labor intensive then LLE and eliminates the need for large volumes of hazardous and expensive solvents. Specific applications investigated include the analysis of ground, surface and tap waters for pesticides, polychlorinated biphenyls and phthalates at the μg l−1 level.

Solid-phase extraction of phenols using membranes loaded with modified polymeric resins

Abstract Membranes impregnated with polystyrene-divinylbenzene (PS-DVB) or acetyl-PS-DVB resin beads were used for solid-phase extraction of ppm (w/w) concentrations of phenols from aqueous samples. A macro procedure uses 47 × 0.5 mm disks with 200–500 ml sample volumes at ca . 200 ml/min flow-rates. A smaller-scale procedure uses a thicker disk (3 mm) packed into a conventional solid-phase extraction column (7 mm I.D.). The retained phenols are eluted from the disk with organic solvent, and the individual phenols are determined quantitatively by GC or HPLC. Recoveries for 16 different phenols, including those included in the US Environmental Protection Agency list of priority pollutants, averaged 98% with a standard deviation of ± 2%.

Gas-solid retention volumes of organic compounds on styrene-divinylbenzene and ethylvinylbenzene-divinylbenzene co-polymer sorbent beads

Reliable gas sampling with a sorbent requires a good knowledge of the gas-solid retention volumes of the analytes on the sorbent. Literature data on specific retention volumes at 20°C (Vg,293, l/g) are reviewed for a number of styrene-divinylbenzene (Sty-DVB) and ethylvinylbenzene-divinylbenzene (EVB-DVB)sorbents, namely XAD-3, Porapak P, Porapak Q, Chromosorb 101, and Chromosorb 102. New measurements are also made by gas-solid chromatography for a Sty-DVB polymer employed in one variety of Empore membrane extraction filters. For all of the data, the log Vg, 293 values are highly correlated with both log pL0 (log of the liquid vapor pressure at 20°C) and with Tb(pure compound boiling point, K). The correlation equations allow the prediction of log Vg,293 based on either log pL0 or Tb. Equations that can be used for a wide range of compounds and a range of Sty-DVB and EVB-DVB sorbents are: log Vg,293 = 1 .16 log pL0 + 3.51, and log Vg,293 = 0.022Tb − 6.60. Separate equations are recommended for aliphatic acids and alcohols. For the Sty-DVB beads used in one variety of Empore extraction filters, the correlation equations are log Vg,293 = 0.99 log pL0 + 3.04, and log Vg,293 = 0.0175Tb =t- 4.97. Most of the available data support absorption into the resin matrix as the dominant gas-solid partitioning mechanism for organic analytes to Sty-DVB sorbent materials.