Resins, nonionic, isolation

Other potential DOP isolation methods are based on sorption using anion-exchange resins or nonionic resins. Extensive research in concentrating humic material has employed these methods (55). For isolation and concentration of DOP, these techniques have several disadvantages, such as possible irreversible sorption onto the resins and the concentration of all anionic species present in the sample. Another major drawback is the need to use a strong base to remove the sorbed material from the resin. For sorption to occur with nonionic resins requires the protonation of all weak acids, thus exposing the sample to low pH. 

A critical review is presented of the methods commonly used to isolate and concentrate aquatic humic substances, important steps in any extraction scheme are filtration, concentration, isolation, and preservation. Various filtration options are outlined and compared filtration is important for obtaining low-ash humic substances. Advantages and disadvantages of commonly used concentration and isolation techniques are discussed, and sorption on the synthetic macroporous resins XAD-8, a nonionic resin, and Duolite A-7, a weak anion-exchange resin, are recommended as the most efficient methods. Two established extraction schemes utilizing these resins are discussed. 

Only 10% of the dissolved organic carbon in seawater has been characterized on a molecular level. About 5 to 23% of this DOC can be isolated from seawater by adsorption onto a nonionic macroporous resin fiallowed by elution with an alkaline solution. 

Adsorption chromatography is an efficient way to isolate organic acids from large volumes of water. The nonionic, macroporous, Amberlite XAD-8 and the weak-base anion-exchange resin Duolite A-7 are two resins well suited for this purpose. These resins have been successfully used to extract organic acids from natural waters at sites where it was necessary to process thousands of gallons of sample. 

Aiken, G. R., D. M. McKnight, K. A. Thorn, and E. M. Thurman. 1992. Isolation of hydrophilic organic acids from water using nonionic macroporous resins. Organic Geochemistry 18 567-573... 

Solid-Phase Extractions Using XAD Resins. The Amberlite XAD series (Rohm and Haas Co., Philadelphia, PA, USA) have been most often used for isolation of marine DOM by SPE. XAD resins are nonionic macroporous copolymers that differ in pore size, surface area, and polarity. Their generally large specific surface areas and more-or-less reversible adsorption of organic solutes from aqueous solution have made them well-suited for isolation of selected fractions of DOM from natural waters. Even though XAD resins have been used far more often to... 

Attempts to develop the sieving process as a tool for the isolation of a pure peptide containing the chromophore were not successful because it was found that the resins did not act as pure ionic sieves (Partridge, 1952) the colored peptides displayed strong adsorptive effects which appeared to be nonionic in character. However it was found that the strong adsorptive affinity of the colored peptides could itself be utilized for further enrichment of the fractions. 

Nonionic surfactants like alkylphenol ethoxylates (APEO) and their biodegradation products alkylphenol diethoxylate (AP2EO), alkylphenol monoethoxylate (APIEO), and AP are isolated from aqueous solutions with a number of different stationary phases. Kubeck et al. ° used C18 cartridges to adsorb NPEO, but first the water samples were passed through a mixed-bed ion exchange resin to remove all ionic species. Eor SPE of alcohol ethoxylates (AEO) C8 cartridges have been successfully applied from which the surfactants were eluted with methanol followed by... 

I, Cationic surfactants from nonionic surfactants Dowex 50-X4, acid form 4—5 g of mixture dispersed in 100 mL water is stirred 4—5 hr with 20 g resin, keeping the mixture acid to Congo red by addition of HCl. The resin is wa.shed with 95% EtOH, the filtrate and washings neutralized and evaporated to dryness, then washed with acetone to isolate the nonionic. 42... 

Isolation from water of alkoxy-lated nonionics AE, NPE, PEG, acid ethoxylates, sorbi-tan ester ethoxylates, E/P copolymers, E/P adducts of alcohols, PPG Anion exchange resin in the cobal-tithiocyanate form, 15 x 200 mm 1 L or more of sample is passed through the column surfactant is eluted with 50 mL MeOH, EtOH, or 2-PrOH. 207... 

The procedures used in column adsorption chromatography may also be used in batch mode, usually with less separation efficiency, but often with some saving of labor. For example, nonionic impurities may be separated from a variety of anionic sulfate and sulfonate surfactants by dissolving the material in a small amount of ethanol/water, mixing with diatomaceous earth, and washing the adsorbant with petroleum ether or 7 93 methylene chloride/petroleum ether. The anionic material remains adsorbed (70). APE may be isolated from water by batch wise separation on XAD-2 resin, 1 g to 0.5-1.0 L of sample. The surfactant is recovered by washing the resin with 100 mL methanol (71). 

Solid phase extraction concentration of nonionics is usually performed with nonpolar Cijj or XAD adsorbants. Cjg resins may be used to isolate carboxylated APE degradation products as well as nonionics (51,97). For PEG determination, glass cartridges are preferred, since a blank value is obtained from conventional cartridges made of polypropylene with polyethylene frits (12). 

Nonionic surfactants are usually isolated from natural waters on XAD resin at neutral pH. This is to prevent the co-adsorption of fulvic acids which occurs under acidic conditions (98). Very hydrophilic metabolites, such as low molecular weight PEG and PEG carboxylates, may not be adequately retained on XAD resin unless the procedures are specifically optimized for these compounds (99). 

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