Lead analysis, sample contamination

Outdoor lead dust was found to be a more potent contaminant of children s hands than indoor lead dust at day care centers in New Orleans boys, in general, had higher hand lead levels than girls. The conclusions were based on lead analysis of hand wipe samples taken before and after children played outdoors at four different day care centers (a private inner-city site, a private outer-city site, a public inner-city site, and a public outer-city site). The private inner-city site had a severely contaminated outdoor play area with measured soil lead concentrations ranging from 287 to 1,878 mg/kg. The outdoor play area at the public inner-city site, where children exhibited the lowest hand lead measurements of any site in the study, had been completely paved over with concrete or rubberized asphalt and had well-maintained equipment (Viverette et al. 1996). 

An interesting example of the contamination risks which may be caused by a laboratory vessel is that of boron. Determination of very low boron concentrations, involves a prior separation by distillation and subsequent analysis by spectrometry, with a suitable reagent such a curcumin or carminic acid. The use of laboratory vessels made of borosilicate glass (such as Duran or Pyrex) could lead to very large errors in the boron content found. Such errors are caused by sample contamination from the boron present in the glassware. 

For instance, air samples and the building material samples contaminated by formaldehyde and lead are routinely sampled by an engineering technician under the supervision of a licenced engineer. The samples are shipped to a certified laboratory for quantitative analysis by the licenced engineer. 

Saxitoxin (STX) is a potent neurotoxin that can cause paralytic shellfish poisoning (PSP). Produced by certain strains of dinoflagellates, saxitoxin leads to the contamination of commercial shellfish and cause severe outbreaks of seafood poisoning. The public health problems caused by these outbreaks have led to significant interest in the development of analytical methods for the analysis of saxitoxin in environmental and biological samples. Saxitoxin is also one of a series of several closely related... 

There are a number of difficulties encountered with quantification after employing derivatization. These include the fact that we are now considering another analytical step, with the concomitent increase in cost and time of each analysis. In addition, because derivatization is another handling stage in the analytical process, there is always the risk of sample contamination. Furthermore, the assumption is made that the derivatization reactions are complete and that the corresponding derivatives are stable for the period between derivative formation and analysis. Further factors are that dilutions need to be extremely accurate and precise to obtain reliable numerical data and that derivatization can potentially lead to increases in numerical errors for such data. 

Contamination may arise from use of solvents within the laboratory or from an adjacent laboratory with a shared ventilation system and can lead to airborne contamination of sample vials and other equipment. Particular care should be taken in the area where samples are handled and transferred and during the preparation of concentrated standard solutions. Many laboratories, particularly where large volumes of solvents are regularly used, find it necessary to have special room, often positively pressurised, for the preparation and analysis of samples for VOCs. Recently decorated rooms can also be a source of VOCs from surface coatings. Contamination can often be intermittent with the wind direction being the controlling factor. 

Other assays that have been used as biomarkers for lead poisoning include lead levels in urine, teeth, hair, and nails (Table XVIII), but none are particularly useful for clinical smdies (5, 10, 436). Urine lead levels can be quantitated easily by AAS but vary widely from individual to individual and are dependent on other parameters (e.g., kidney function) that are difficult to normalize. Urine lead levels are used extensively, however, to monitor the progress and effectiveness of chelation therapy (see below) (10). Lead levels in teeth are a good measure of cumulative lead exposure and can be measured using either AAS, ICP-MS, or ASV, but are not very useful on a practical level because the analysis requires shedding of teeth (10, 524). Hair and nails would appear the ideal source of materials for lead analysis because they are easily procured and rapidly regenerate, but lead levels in hair and nails vary considerably from individual to individual, and these samples are highly susceptible to contamination. 

Cryostats are normally used as a standard tool for slicing frozen tissue to reducing sample contamination. Contamination of the tissue surface due to the use of OCT (optimal cutting temperature polymer) as an embedding medium for stabilizing the organ specimens should be avoided because it would lead to ionization suppression in MALDI-MS analysis. 

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

As plant extracts mainly comprise large amonnts of ballast substances (e.g., lipids and chlorophylls), their purification is often a priority in the analysis. Such purification can be expensive in terms of both time and solvent consumed and can lead to losses of sample components. Online purification and separation of extracts contaminated with plant oil, can be readily performed by TLC in equilibrium chambers [1] that enable the use of continuous elution. 

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... 

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