Resins artifacts

Artifacts from the resin can interfere with the chromatographic analysis of the XAD resin extract. For example, the artifact may be a pollutant being studied, or coelution of the resin artifacts and compounds of interest may occur during capillary gas chromatographic (GC) analysis. Artifacts can also take part in competitive adsorption during sampling. This situation can cause sample breakthrough because certain compounds are preferentially collected. 

Table IV. Solubility Parameters for Selected XAD Resin Artifacts...

Use of the resins with samples containing free chlorine residual is not recommended. Cheh (35) suggested that chlorine may produce mutagenic artifacts on XAD-4. Our experiment with 2-mg/L chlorine residual appeared to promote the release of irreversibly adsorbed spiked standards Six model compounds were recovered at levels several times higher than those observed in normal blank runs. In addition, many resin artifacts were eluted after exposure to this chlorine level, primarily aromatic and aliphatic acids, aldehydes, and ketones. Stoichiometric dechlorination (ferrous ion) is therefore recommended in order to avoid cross contamination between samples and inclusion of undesirable resin artifacts in the residue to be bioassayed. 

The use of urea must be approached with caution, because urea solutions often contain ammonium cyanate, the concentration of which increases with temperature and pH. This contaminant can react with the amino group of lysines and the amino terminus of the polypeptide chain, thus leading to artifact peaks. This effect is minimized by the presence of ampholytes, whose primary amines are cyanate scavengers, and by deionizing the urea solution with a mixed-bed resin prior to adding the ampholytes and detergent. 

Lysine on Wang resin swollen in CDC13 and spun at 5 kHz. The inset shows the low artifact level of the spectrum. Reproduced with permission from Ref. 42. Copyright 1996 American Chemical Society. 

Furthermore, many bioassay procedures can be affected synergis-tically or antagonistically by artifacts. In current practice, chemists use various solvents to clean the resin as completely as possible, run a resin blank, and chromatographically analyze the blank sample. Rarely are the artifacts identified. This procedure does not help the biologist who requires a blank that does not show a positive response in the bioassay test of the blank. Biologists usually clean the resin as the chemists do and complete a blank for the bioassay. Artifacts should be identified to assure that the bioassay results are in response to the compounds under study and not the artifacts in combination with the sample. 

Results from the fourth elution show that there are artifacts from the resins after elution with 2.5 bed volumes of solvent. These artifacts are found at very low levels—less than 0.3 parts per trillion in 150 L of water (see Figure 2). 

Artifacts. The following hypotheses have been presented to explain the presence of the artifacts occurring during sampling and elution of the resin after it is initially cleaned ... 

This quality assessment study indicates that to use resins for broad spectrum analysis, the resin elution, storage, cleaning, and reuse procedures must be rigorously defined so that the artifacts produced do not interfere. Once the procedures have been defined, they must be strictly followed. 

Tentatively Identified Artifact Contaminants from Resin Fractionation Scheme... 

Synthetic sorbents are known to contain artifacts in the resin that could be eluted during desorption of the organic compounds concentrated on the resin. Therefore, separate experiments using XAD-4 quaternary resin (OH form) were also performed to evaluate the presence of artifacts, either those arising from the interaction of chlorine with the resin or those from the resin itself. 

Resin Blank Artifacts Effect of 2 ppm of Residual Chlorine. Three basic types of blank experiments were performed. One was performed to identify any artifacts caused by the presence of 2 ppm of chlorine in blank water used in the separation-concentration procedure, and another was performed to identify any artifacts in the general resin procedure. In addition, a reagent blank was also concentrated and analyzed. The reagent blank was performed in a manner identical to the pure water blanks, except that no resin was included in the procedure. This reagent blank gave an indication of contaminants arising from sources other than the resin (i.e., glassware, water, solvents). 

Clean Water Blank Experiment. This experiment was performed for the purpose of identifying any artifacts that might arise from the resin in the course of normal resin experiments. Four replicate resin blanks were run by the normal resin separation-concentration procedure. Data from this experiment yielded the following conclusions ... 

None of the alkyl-substituted aromatics identified as artifact contaminants from XAD-2 resin by USEPA-Battelle were identified in this experiment. 

The XAD-4 quaternary resin was cleaned by Soxhlet extraction and kept wet under water to minimize artifacts from the resin. An oily, yellow residue observed during concentration of the acidic eluants required an additional cleanup step. On the basis of the results of the resin blank experiments, it was necessary to clean the XAD-4 quaternary resin by batch process with saturated HCl/methanol prior to Soxhlet cleaning with solvents. Artifacts such as benzoic acid were found in the resin blank experiments, but, in general, the mass of each artifact (per dry weight of resin) was negligible. 

The specimens are then immersed in a molten wax or natural resin and the Cellosolve slowly distilled off. This step invariably involves some shrinkage. Antishrink efficiencies of 80% are, however, obtainable in this way with mixtures of beeswax and rosin. This treatment appears suitable for the preservation of wood artifacts. Christensen (43) has treated wood artifacts by replacing the water with tertiary butanol and this with polyethylene glycol-4000. 

Chemistry, Physics, and Biology Laboratories. As a rule, before any artifact is subjected to treatment, the chemistry laboratory determines the causes of any alterations or deterioration. The nature and structure of the artifact, its pigments and inks, are identified to avoid negative reactions to prescribed treatment. Fixatives are recommended if required these may be cellulose acetate dissolved in acetone, soluble nylon, or acrylic resin sprays. Once stains are identified, several possible solvents are selected. For deacidification, either magnesium bicarbonate or barium hydroxide usually is recommended, depending on whether an aqueous or nonaqueous solution is called for. Bleaching is discouraged, but when necessary, hypochlorites are used with suitable antichlors. 

Parchment Shop. There are five restorers in this shop. Parchment documents and book covers to be restored get a mechanical surface cleaning with soft erasers then harder ones, if required, to remove dirt and grime. Hard, embrittled, and dry artifacts have their inks and pigments fixed with an acrylic resin spray or with a fine brush dipped in paraloid before immersion in a bath of ethanol and water (70% and 30%, respectively). 

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