Lead, analytical contamination

Samples are pre-concentrated in order to allow detection to be achieved. This is required when the concentration of analyte in the sample is too low or when as a result of pre-treatment the concentration in the resulting solution is too low for detection. Care is needed in any pre-concentration procedure to ensure that it does not lead to contamination from, for example, the equipment or chemicals used. 

Although the products of biotic and abiotic processes of this compound in the environment are adequately known, no systematic study is available that measured the concentrations of its reaction products in the environment. In instances where the product(s) of an environmental reaction is more toxic than the parent compound, it is important that the level of the reaction products in the environment be known. It is known that 1,1,2-trichloroethane under anaerobic conditions (e.g. in anaerobic soils leading to contamination to groundwater) may dehydrochlorinate to vinyl chloride (see Section 5.3), a compound more toxic than the parent compound. The analytical methods for the determination of the levels of these and other environmental degradation products of... 

Chromatographic techniques require various procedures to isolate the drugs from biological matrices. In the reviewed methods, two distinct approaches are applied liquid-liquid extraction and direct injection into a chromatographic system. Diethyl ether and ethyl acetate,chloroform,toluene, benzene, methyl r-butyl ether, and n-butyl chloride are used as solvents to obtain recoveries well over 80% for all considered compounds. However, manual sample preparation can be labor and time intensive. Therefore, direct injection is used as a highly automated methodol-ogy. The direct injection of complex samples, however, may lead to contamination of columns, thereby impairing their performance. Contamination often persists, even when a precolumn is used to protect the analytical column. A summary of these chromatographic methods for determination of sulfonylureas is presented in Table 1. 

The prerequisite for implementing MS in biochemical analysis is that the analytes are amenable to ionization using one of the available ion sources (cf. Chapter 2). A vast majority of biochemical processes occur in the condensed phase. Most enzymes are active in aqueous solutions while only a few of them can catalyze reactions in organic solvents (e.g., transesterification catalyzed by lipase [5]). Water-based buffers are not always the optimum solvents for the operation of ion sources. In fact, concentrated buffer solutions - which are often used in biochemical assays - can suppress ionization, and lead to contamination of... 

Analytical determination of the chemical as well as the radiochentical composition of the different substances that play a role in the production as well as in the transport and deposition of the radionuclides of interest, is a very important tool for the elucidation of the mechanisms leading to contamination buildup. For this reason, a short survey will be given in the following of the available anal dical methods with particular emphasis on those that can be used with the coolants and components of the primary systems of nuclear power plants. 

While the stringent procedures required to control lead contamination of samples have been detailed in several reports (e.g., Flegal and Smith 1992b NRC 1980, 1993 Settle and Patterson 1980 Versieck et al. 1982) in addition to those previously cited, many laboratories still have not adopted these requisite procedures for measuring low levels of lead. Analytical reagents and inadequately cleaned labware, as well as contaminated sample... 

Most aroma chemicals are relatively high boiling (80—160°C at 0.4 kPa = 3 mm Hg) Hquids and therefore are subject to purification by vacuum distillation. Because small amounts of decomposition may lead to unacceptable odor contamination, thermal stabiUty of products and by-products is an issue. Important advances have been made in distillation techniques and equipment to allow routine production of 5000 kg or larger batches of various products. In order to make optimal use of equipment and to standardize conditions for distillations and reactions, computer control has been instituted. This is particulady well suited to the multipurpose batch operations encountered in most aroma chemical plants. In some instances, on-line analytical capabihty is being developed to work in conjunction with computer controls. 

Cathodic protection with impressed current, aluminum or magnesium anodes does not lead to any promotion of germs in the water. There is also no multiplication of bacteria and fungi in the anode slime [32,33]. Unhygienic contamination of the water only arises if anaerobic conditions develop in the slurry deposits, giving rise to bacterial reduction of sulfate. If this is the case, HjS can be detected by smell in amounts which cannot be detected analytically or by taste. Remedial measures are dealt with in Section 20.4.2. 

The limitations of SIMS - some inherent in secondary ion formation, some because of the physics of ion beams, and some because of the nature of sputtering - have been mentioned in Sect. 3.1. Sputtering produces predominantly neutral atoms for most of the elements in the periodic table the typical secondary ion yield is between 10 and 10 . This leads to a serious sensitivity limitation when extremely small volumes must be probed, or when high lateral and depth resolution analyses are needed. Another problem arises because the secondary ion yield can vary by many orders of magnitude as a function of surface contamination and matrix composition this hampers quantification. Quantification can also be hampered by interferences from molecules, molecular fragments, and isotopes of other elements with the same mass as the analyte. Very high mass-resolution can reject such interferences but only at the expense of detection sensitivity. 

As more sensitive analytical methods for pesticides are developed, greater care must be taken to avoid sample contamination and misidentification of residues. For example, in pesticide leaching or field dissipation studies, small amounts of surface soil coming in contact with soil core or soil pore water samples taken from further below the ground surface can sometimes lead to wildly inaccurate analytical results. This is probably the cause of isolated, high-level detections of pesticides in the lower part of the vadose zone or in groundwater in samples taken soon after application when other data (weather, soil permeability determinations and other pesticide or tracer analytical results) imply that such results are highly improbable. 

Another consideration when planning field fortification levels for the matrices is the lowest level for fortification. The low-level fortification samples should be set high enough above the limit of quantitation (LOQ) of the analyte so as to ensure that inadvertent field contamination does not add to and does not drive up the field recovery of the low-fortification samples. Setting the low field fortification level too low will lead to unacceptably high levels of the analyte in low field spike matrix samples if inadvertent aerial drift or pesticide transport occurs in and around where the field fortification samples are located. Such inadvertent aerial drift or transport is extremely hard to avoid since wind shifts and temperature inversions commonly occur during mixer-loader/re-entry exposure studies. 

One alternative method for preparing field fortifications solutions/suspensions is to prepare each fortification sample of each matrix in a separate mini-vial in the analytical laboratory and ship the vials to the field for use. This procedure precludes the use of pipets in the field and may be useful when Field Scientists not experienced in the use of pipets are involved in the field fortification process. One disadvantage of this procedure is that the mini-vials, if not designed correctly, will be hard to handle in the field, and surface tension of the suspension or fortification solution will tend to leave unacceptable amounts of the solution/suspension in the vial or at the lip of the vial and not on the matrix in question. This procedure may lead to cross-contamination of samples as the field fortification liquid is forced from the top... 

The efficiency of the machinery employed is discussed, pertinent supporting analytical data are presented, and the sensitivity of the color reaction, leading to unbelievably easy contamination, is stressed. Over processing in all steps is recommended as a means of nullifying inherent variations in the efficiencies of different types of processing apparatus used by other workers. 

By the nature of the process by which olive oil is extracted from the olive, the oil is susceptible to contamination. The high price associated with olive oil of the highest purity— extra virgin olive oil — also leads to falsification by unscrupulous vendors who blend with less costly oils such as com, peanut, and soybean oil. Various analytical techniques have been devised to authenticate the purity of olive oil by detecting certain oil components. 

Several matrix modifiers, which alter the drying or charring properties of the sample matrix, have been tested [374-378] to reduce nonspecific absorption. However, the matrix modification methods do not permit determinations of the indigenous lead in seawater because of the relatively high detection limit and poor precision, and yet gross chemical manipulations of the samples should be avoided to prevent contaminations which can be dramatic when the analyte is present at p,g/l or sub- xg/l level. 

In contrast, the coupling of electrochemical and spectroscopic techniques, e.g., electrodeposition of a metal followed by detection by atomic absorption spectrometry, has received limited attention. Wire filaments, graphite rods, pyrolytic graphite tubes, and hanging drop mercury electrodes have been tested [383-394] for electrochemical preconcentration of the analyte to be determined by atomic absorption spectroscopy. However, these ex situ preconcentration methods are often characterised by unavoidable irreproducibility, contaminations arising from handling of the support, and detection limits unsuitable for lead detection at sub-ppb levels. 

The ability to provide data on the isotopic composition of analyte elements, is a further special feature of the technique. This has already been exploited in a number of ways, including geological dating and the identification of sources of environmental lead contamination and poisoning. The radiogeneric source of lead means that different deposits may have different isotopic composition. In the UK this feature has been used to... 

Atmospheric contaminants from smelting works or combustion processes eventually enter the natural drainage system as fall out, and are carried into the rivers. It is probable that the deposition of sediments and the higher pH of marine water, which leads to precipitation, results in a build-up of the heavy metal pollutants in the river estuary. An assessment of this build-up is essentially an analytical problem. 

The most straightforward tool for the introduction of a sample into a mass spectrometer is called the direct inlet system. It consists of a metal probe (sample rod) with a heater on its tip. The sample is inserted into a cmcible made of glass, metal, or silica, which is secured at the heated tip. The probe is introduced into the ion source through a vacuum lock. Since the pressure in the ion source is 10-5 to 10-6 torr, while the sample may be heated up to 400°C, quite a lot of organic compounds may be vaporized and analyzed. Very often there is no need to heat the sample, as the vapor pressure of an analyte in a vacuum is sufficient to record a reasonable mass spectrum. If an analyte is too volatile the cmcible may be cooled rather than heated. There are two main disadvantages of this system. If a sample contains more than one compound with close volatilities, the recorded spectrum will be a superposition of spectra of individual compounds. This phenomenon may significantly complicate the identification (both manual and computerized). Another drawback deals with the possibility of introducing too much sample. This may lead to a drop in pressure, ion-molecule reactions, poor quality of spectra, and source contamination. 

Fate-and-transport studies using computer modeling and mathematical calculations can effectively evaluate the potential for contaminant migration and degradation through the natural and anthropogenic processes active at the site. Often a brief fate-and-transport study early in the project can lead to optimal placement of monitor and recovery wells, and selection of sample analytical procedures. 

Therefore, methods for the analysis of total petroleum hydrocarbon are frequently used to find areas of gross contamination but are often inadequate even for this task. Indeed, any one of several variables, such as differences in moisture content, can lead to analytical inconsistencies, and therefore the data do not consistently give reliable insights as to which part of the site is most contaminated. 

Most solder contains elements such as lead, tin, antimony, etc. Current passage through such metals could readily lead to their oxidation, with subsequent contamination of the analyte solution. Furthermore, such redox processes greatly complicate - if not invalidate - any coulometric analyses. 

---