Contamination during analysis

Having received the pre-weighed test item, preparation for its use in the field must be made. Ideally, water to be used in the dilution of the test item should be from mains water or a recognized source. The use of water from standing pools, rivers, etc., could potentially lead to problems with interference from contaminants during analysis of the crop samples. Depending on the formulation under test, the test item can be mixed in a variety of ways. First, the required water volume must be accurately measured. Approximately half of this amount can be poured into a clean bucket or similar mixing container. The temperature of the water should be noted at this point... 

If the samples are to be brought back to a shore laboratory for analysis, contamination during analysis is more easily controlled. The analyst on shore must have confidence in the people taking the samples with the pressure on berth space and wire time on board ship, too often the samples are taken on a while you re out there, take some for me basis. Again, ideally, the analyst should at least oversee every part of the process, from the cleaning of the sampler to the final calculation of the amounts present. His confidence in the accuracy of the final calculation must decrease as he departs from the ideal arrangement. 

Drift Correction Can be observed in the results as a function of time (or sample number) and can be caused by a range of factors, including isotopic change in the reference gas, buildup of water or other contaminants during analysis, changing MS conditions, deterioration of the ion source, and so on ... 

The total blank is determined by extracting 100 g of ultrapure water and has usually been found not to differ from the reagent blank (of the order of 0.01 nmol/L). Random sources of contamination during analysis under clean-room conditions therefore can be neglected. 

This technique " is particularly useful for ultra-trace analysis of solid samples in that it eliminates most of the problems of reagent blanks and/or sample contamination during analysis. The large number of variables (such as type and energy of irradiating particle, time of irradiation and measurement, type of detector used, etc.) that can be judiciously altered for particular analyses make the technique relatively free from serious systematic errors or biases. A typical value for the random errors is + 5 % at the 100-ng level. 

The vacuum requirements in the target chamber are relatively modest (10 Pa) and are comparable to those in the accelerator beam lines. All that is required is that the ion beam does not lose energy on its path to the sample and that there is minimal deposition of contaminants and hydrocarbons on the surface during analysis. 

Methods for iodine deterrnination in foods using colorimetry (95,96), ion-selective electrodes (94,97), micro acid digestion methods (98), and gas chromatography (99) suffer some limitations such as potential interferences, possibHity of contamination, and loss during analysis. More recendy neutron activation analysis, which is probably the most sensitive analytical technique for determining iodine, has also been used (100—102). 

S prevention of contamination during sampling and analysis has been inadequate leading... 

Kinetic Analysis. Gas chromatographic analysis of the headspace gases confirms that the predominant reaction product is CO.. The negligible presence of N and 0 are probably due, at least in part, to air contamination during sample preparation for the GC analysis. The results of the GC analysis are shown in Table II. 

Industrial analytical laboratories search for methodologies that allow high quality analysis with enhanced sensitivity, short overall analysis times through significant reductions in sample preparation, reduced cost per analysis through fewer man-hours per sample, reduced solvent usage and disposal costs, and minimisation of errors due to analyte loss and contamination during evaporation. The experience and criticism of analysts influence the economical aspects of analysis methods very substantially. 

Two practical problems in the analysis of plastics by NAA, namely contamination during sample preparation... 

The first structural study of a UPD layer involved the formation of a series of Agl monolayers on Pt(lll) single crystals [132, 133], Pt is the quintessential catalytic metal, and thus reacts with almost any organic compound, other than simple alkanes [134], in other words, it is easily contaminated. In the early days of UHV-EC studies, contamination during transfer of Pt single crystals from the analysis chamber to the electrochemical cell and back was the chief stumbling block to well-defined studies of... 

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. 

These data are based on advanced instrumentation and sampling methodology, paying attention to the elimination of contamination during sampling, storage, and analysis. See article by Windom et al. (1991) from where the data for this table are taken. 

Based on the examination of analytical data from polychlorinated biphenyls (PCBs), OCPs and PAHs spiked into SPMDs, which have subsequently been subjected to the entire SPMD analytical procedure described herein, recoveries are generally >75% with good precision (i.e., C.Fs < 20%). Surprisingly, the C. Vis for the analysis of contaminants present in replicate SPMDs deployed contiguously at the same sites and treated identically during analysis are often equivalent to C.Fs of SPMD spikes. This observation suggests that the variability of analyte sampling rates of replicate SPMDs in the field is small and that the analytical methods used for field-deployed SPMDs are robust. 

Use extreme caution when obtaining samples for TOC analysis. Water samples can be easily contaminated during the process of sampling and transportation to the testing facility. 

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