Aqueous samples contaminated

Prior to injection, aqueous samples were collected from U2 and U3 in order to establish the methodology and baseline conditions. The samples were contaminated with kill fluid and the succession from the first samples shows a decrease in K and increase in most other species. Subsequent samples continued to show some contamination but it was determined that essentially baseline conditions had been achieved except for... 

Several attempts have been made to set up immunochemical techniques for dioxin analysis (reviewed in [230,238,239]). Frequently the detectability and selectivity accomplished have not been considered appropriate for the direct analysis of environmental samples. We should notice that due to the poor solubility of PCDDs and PCDFs in water, the levels of these contaminants in aqueous samples is very low. For this reason analysts usually prefer the use of chromatographic and spectrometric methods that perform using organic solvents. However, the speed and high sample throughput that can be accomplished with the immunochemical methods have prompted several research groups and companies to establish immunochemical methods. 

Modern methods of sample handling for determination of surfactants in aqueous samples are practically all based on SPE and modifications thereof. Substantial reductions in analysis time, solvent consumption, sample volume required, and number of off-line steps have thus been achieved. This has not only increased the analysts capacity and analysis price per sample, but also decreased the risk of both analyte loss and contamination during sample handling. Whether or not this has indeed resulted in an increased quality of analytical results still needs to be validated through, e.g. intercalibration exercises. This aspect is discussed in more detail in Chapter 4. 

Nodler K, Licha T, Bester K et al (2010) Development of a multi-residue analytical method, based on liquid chromatography-tandem mass spectrometry, for the simultaneous determination of 46 micro-contaminants in aqueous samples. J Chromatogr A 1217 6511-6521... 

Detection limits in the range of low parts per billion (ppb) can be achieved by immunoassay testing for certain parameters in aqueous samples. For soil samples, detection limits of <10 ppm can be achieved for many contaminants... 

DNPH is often susceptible to formaldehyde or acetone contamination. It should, therefore, be crystallized with acetonitrile to remove any impurities. Repeated crystallization may further be performed to achieve the desired level of purity for DNPH. A 100-mL aliquot of aqueous sample is buffered with a citrate buffer and pH adjusted to 3 0.1 with HC1 or NaOH. The acidified sample is then treated with DNPH reagent and heated at 40°C for an hour under gentle swirling. The DNPH derivatives of aldehydes and ketones formed according to the above reaction are extracted with methylene chloride using liquid-liquid extraction. The extract is then solvent exchanged to acetonitrile for HPLC determination. 

Aqueous samples are extracted with methylene chloride. If the sample is not clean or if the presence of organic interference is suspected, a solvent wash should be performed. For this, the pH of the sample is adjusted to 12 or greater with NaOH solution. The sample solution made basic is then shaken with methylene chloride. Organic contaminants of basic nature and most neutral substances partition into the methylene chloride phase, leaving phenols and other acidic compounds in the aqueous phase. The solvent layer is discarded. The pH of the aqueous phase is now adjusted to 2 or below with H2S04, after which the acidic solution is repeatedly extracted with methylene chloride. Phenols and other organic compounds of acidic nature partition into the methylene chloride phase. The methylene chloride extract is then concentrated and exchanged into 2-propanol for GC analysis. For clean samples, abasic solvent wash is not necessary however, the sample should be acidified before extraction. It may be noted that basic solvent wash may cause reduced recovery of phenol and 2,4-dimethylphenol. 

Aqueous background samples are collected from similar sources (i.e. upstream of effluent output, puddles of water, tap water, etc.) outside the possibly contaminated area. If a background aqueous sample cannot be collected, tap water or deion-ized/distilled water can be used as a background sample. 

It appears likely that these formulations referred to samples contaminated by hydroxo impurities. The cis-dinitrosyl complexes [Ph4P]2[Mo(CN)4(NO)2] H2O and [Mo(CN)2(phenXNO)2] H20 are prepared by adding KCN and [HONH3]Cl to an aqueous solution of Na2Mo04 and NaOH, followed by acidification with HCl and addition of [Ph4P]Br or phen, respectively . 

Aqueous samples are treated similarly beginning with the acidification step. The entire sample is then put through the hydrophobic resin, and the fulvic acids are eluted at pH 7. The humic acids are removed with 0.1 M NaOH (2). After extraction, purification of the samples can be accomplished by freeze-drying and dialysis. The use of strong acids and bases has been criticized for several reasons. They can promote degradation, decarboxylation, oxidation, and condensation reactions. Strong acids and bases can also dissolve siliceous materials and lyse cells, resulting in contamination of the sample. Other extractants have been proposed, such as sodium pyrophosphate or sodium fluoride however, the classical procedure offers the most complete dissolution of humic material from solid samples and is still most often used (72). 

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