Soil, lead detection limits

High-resolution GC equipped with an appropriate detector is the most common analytical technique for determining the concentrations of 1,2-dibromoethane in air, water, wastewater, soil, leaded gasoline, and various foods (e.g., grains, grain-based foods, beverages, and fruits). The choice of a particular detector will depend on the nature of the sample matrix, the detection limit, and the cost of the analysis. Because volatile organic compounds in environmental samples may exist as complex mixtures or at very low concentrations, concentrations of these samples prior to quantification are... 

According to the vendor, Cement-Lock technology has successfully removed polycyclic aromatic hydrocarbons (PAHs), PCBs, and tetrachlorodibenzo-1,4-dioxin (TCDD)/2,3,7,8-tetra-chlorodibenzofuran (TCDF) from soils and sediments in bench-scale tests. Metal concentrations were also reduced below detection limits in bench-scale tests. These metals included arsenic, cadmium, chromium, lead, nickel, mercury, and silver. 

West and co-workers11 achieved far greater sensitivity enhancement by trapping readily atomized elements, which had been nebulized conventionally for periods of up to a few minutes, onto the outer surface of a small bore, water-cooled quartz tube. If the water was then drained rapidly, the tube temperature quickly rose and the element was atomized off the surface. For cadmium in calcium chloride extracts of soil, for example, a detection limit of 4 ng (g soil) -1 was reported. A water-cooled double silica tube atom trap similarly has been very successfully employed for the determination of cadmium and lead in natural waters by flame AAS.12 Some further examples of applications of atom trapping are included in Chapter 7. 

Ion-selective electrodes are used for many applications but most commonly for the measurement of pH and metal ions such as tin , lead silver and nickeT as well as various other analytes such as surfactants". The samples investigated range from surface waters, e.g. lakes and streams, ground waters, rain, to soil and food. ISEs for anion detection are not as prevalent due to solubility issues but more are becoming available, such as one for iodide with a detection limit of 5.3 X 10 and with the help of ionic liquids another has been developed for sulfate detection". 

Detection limits for lead in soil matrices have markedly improved over the last several decades owing to improvements in the signal detection systems, e.g., charge-coupled devices in place of photomultipher tubes. 

Lead in diet occm at lower concentrations than in a number of other media, e.g., soils and dusts. Measurement methods therefore require high sensitivity for detection. Lead levels were originally measured by conventional A AS, but now there is more use of bulk sample ashing and Flameless AAS. Capar (1991) described a food lead quantitation limit of 20 ppb. 

The standard solutions and eight sample solutions were analyzed using a ThermoElectron S Series Flame Atomic Absorption Spectrophotometer and an air-acetylene flame and equipped with a Pb hollow-cathode lamp detecting at 283.3 nm, a Co hollow-cathode lamp, and a Cd hollow-cathode lamp. The sample solutions gave absorbance at or very near the lowest standard employed, which was just above the detection limit of the instrument. Using 0.022 ppm Pb as the detection limit leads to an upper limit of 20 ppm Pb + in the original soil samples. The 20-ppm value equates to 0.02 mg/kg for Pb. The Cd concentrations were lower than 1 ppm, which equates to 0.001 mg/kg Cd. 

All of the soil samples from the compostable materials had lead concentrations much lower than the limit of 30 mg/kg Pb and Cd concentrations lower than the limit of 17 mg/kg Cd. In fact, the measured values for Pb and Cd were at the lower detection limits of the Pb and Cd detectors. 

Spot test Idts being developed for dust are also designed to indicate the presence of lead in soil. These kits will be evaluated in terms oftheir extraction requirements, detection limit, and the fi-equency and circumstances of false positives and negatives. A portable XRF instrument for soil measurements has been developed for larger sites typical of superfund clean-up operations, it is being adapted for use in an urban soil setting. 

Official methods have been published for the determination of nitric-perchloric acid-soluble lead [111] and ammonium pyrrolidine dithiocarbamate-extractable lead [ 112] in soil. Atomic absorption spectrometric evaluations of the digest or extract is conducted at the 217 nm emission line from a lead hollow cathode lamp. Rigin and Rigina [122] determined lead in soil by flameless atomic fluorescence using electrolytic preconcentration. The limit of detection is 15 pg lead and the standard deviation is not greater than 0.04. 

Solvent extracts are analysed by an HPLC system with a UV and/or fluorescence detector. The chromatogram can produce either a total PAH result, or can be fine-tuned to give speciated compounds. The method is specific and sensitive, but may suffer from co-elution, and the limit of detection for each PAH is 1 mg/kg. For soil analysis, this is not the preferred technique as build up of matrix components on the HPLC column can result in small shifts in retention times leading to mis-identification of peaks. 

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