Membrane extraction disks

C Aguilar, F Borrull, RM Marce. On-line and off-line solid-phase extraction with styrene-divinylben-zene-membrane extraction disks for determining pesticides in water by reversed-phase liquid chromatography-. J Chromatogr A 754 77-84, 1996. 

E. R. Brouwer, H. Lingeman and U. A. Th Brinkman, Use of membrane extraction disks for on-line trace enrichment of organic compounds from aqueous samples , Chromatographia 29 415-418 (1990). 

Tomkins BA, Griest WH. Determinations of N-nitrosodimethylamine at part-per-trillion concentrations in contaminated groundwaters and drinking waters featuring carbon-based membrane extraction disks. Anal Chem 1996 68 2533-2540. 

Particle-loaded membrane extraction disks, the so-called Empore disks, form an alternative to SPE cartridges [27, 78-79]. With Empore disks, higher sampling flow-rates are possible. They show excellent sorbent capacity. Recoveries at 0.1-pg/l level... 

Ware GM, Price G, Carter L, Eitenmiller RR (2000) Liquid chromatographic preparative method for isolating ergot alkaloids, using a particle-loaded membrane extracting disk. J AOAC Int 83 1395-1399... 

Amperometric Glassy carbon +1100 mV vs. Ag/AgCl Polyfstyrene-divinylbenzene) (PS-DVB) membrane extraction disk River water and tap water [209]... 

Schematic of apparatus for membrane extraction disks. (From http //solutions.3m.com/wps/portal/ 3m/en us/Empore/extraction/products/disks/ accessory-products. With permission.)...

High concentration of nontargeted ionic contaminants may reduce the efficiency of the 3M Empore extraction disk. Due to the high loading capabilities of the Empore membranes, the radionuclide concentration on the filters must be monitored to ensure that the membranes do not exceed the limits for low-level radioactive waste. 

Fig 1. 1 pmol Parathyroid Hormone Fragment 39-68 (PHF), lOpmoI Pigeon Heart Cytochrome C (PHC), 10 pmol Bovin Serum Albumin (BSA) in saturated sinapinic acid matrix, desorbed from a. Polyethylene Membrane 113-2 b. Polypropylene Membrane 1222 c. Type 61 Disposable IR Card d. C8 Extraction Disk e. C18 Extraction Disk. 

In general, MALDI of samples fixed to membranes resulted in no loss of mass resolution or mass range. Spectra were extremely reproducible, and could usually be acquired at a lower threshold laser intensity. Figure 1 shows a peptide and protein mixture desorbed from each of the 5 tested membranes. All membranes except the CIS extraction disk produced well resolved spectra. Higher masses were better resolved in samples fixed to polyethylene membranes, while lower masses were better resolved by fixing samples to the Type 61 disposable IR card. Doubly and triply charged ions formed more readily upon desorption/ionization from all the membranes tested, than from stainless steel surfaces. 

Of the several membranes we examined, the polyethylene membranes were the most effective under all conditions. More specifically, the 113-2 membrane was most effective, followed by the IR membrane. The polypropylene membrane 1222 was the next most effective, followed by the C8 and C18 extraction disks. We suspect that the smaller pore sizes of polyethylene membranes results in retention of peptides and proteins at the membrane surface. Further work is need to establish this, however. 

In addition to packed cartridges, solid-phase extraction can be can ied out by using small membranes or extraction disks. These have the advantages of reducing extraction time and reducing solvent use. Solid-phase extraction can be done in continuous flow systems, which can automate the preconcentration process. 

One recent application in lEC consists of solid phase extraction disks which are used to eliminate matrix interference prior to analysis. The disk contains a membrane composed of resin beads enmeshed in a PTFE membrane, housed in a polypropylene housing. The resin is treated to remove specific ions such as H+ to remove hydroxide, Ag+ for excess halides and Ba to remove sulphate. Other disks such as hydroxide for acid removal and neutral styrene-divinylbenzene to eliminate hydrophobic components which can damage resin based IC columns are being developed [23]. 

Implementing SPE in flow analysis without mini-columns is also feasible. To this end, other materials, e.g., commercially available ion-exchange or chelating extraction disks [231], disposable extracting cartridges [232], polymer-composite membranes [233] and monolithic columns [212], have been used. Analytical procedures exploiting addition, transport and disposal of the solid particles, analyte sorption/ elution in flow reversal, and the use of fluidised beads have also been proposed, as highlighted at the end of this section. 

The development of extraction disks (e.g., Em-pore ) cartridges and syringe barrels has proved to be a convenient and attractive tool for the enrichment of trace organic materials from natural waters. Such units may consist of membranes of PTFE fibrils in between which are incorporated particles of adsorbent materials such as Cg, Cig, ion exchange resins, or polymer-based materials. These disks are in some ways more convenient than columns and may be... 

A recently developed variant of solid-phase extraction is extraction with the aid of extraction disks [220J. [221], membrane filter plates on which an appropriate solid-phase material has been immobilized. Advantages of extraction disks include higher flow rates and more rapid material exchange. Another variant involves the use of SPE for simultaneous extraction and derivatization. For this purpose the analyte is adsorbed onto a solid... 

PTFE membranes loaded with particles of silica gel or chemically bonded silica gel are a relatively new type of flexible support developed for TLC (97-99). These Empore sheets, which are similar to Empore extraction disks used for solid phase extraction (100), are especially useful for recovery of separated samples in preparative layer chromatography or scintillation counting of radioisotopes by cutting out sections of the chromatogram containing the analytes of interest. Empore sheets have lower efficiency than conventional thin layers (29) and have not yet been applied widely for TLC. 

A separation of °Bi and °Po from Pb through uses of solid-phase extraction disks in aqueous environmental samples was presented by Marley et al. [98]. In this method, the extraction membrane can be counted directly for °Bi and °Po. If sufficient time is allowed for ingrowth of the daughter, the concentration of the parent °Pb in the original sample can be determined as well. 

P. J. M. Kwakman, J. J. Vreuls, U. A. Th Brinkman and R. T. Gliijsen, Determination of organophosphonis pesticides in aqueous samples by on-line membrane disk extraction and capillary gas cliromatography , Chromatographia 34 41-47 (1992). 

A modification of the RDC design, based on the ring-disk arrangement of the RDE [36], incorporated an arc electrode [37,38] deposited on the surface of the membrane around the untreated area. This facilitated the electrochemical detection of species reacting at the interface at short times following the reaction. This method was used to study the solvent extraction of cupric ions, which were detected by reduction to copper metal at the arc electrode. The resulting current flow was related to the interfacial flux at the membrane. 

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