Determination of Labile Cadmium in Agricultural Soils by Isotope Dilution Plasma Mass Spectrometry and a Coprecipitation Separation Technique

Abstract

Isotope dilution techniques were examined in order to determine the E-value (isotopically exchangeable pool or labile pool) of cadmium (Cd) in uncontaminated soil. In order to avoid spectral interference, coprecipitation separation was applied before taking inductively coupled plasma mass spectrometry (ICP-MS) measurements. An enriched 113 Cd solution was added to a soil suspension (15 g of soil and 150 mL of water) and then a 2 mL aliquot of it was sampled and filtered immediately at different exchange times. By addition of a sodium hydroxide solution to the filtered solution, Cd coprecipitated with major constituents in the filtered solution, such as iron and magnesium. After the supernatant was discarded, the precipitate was dissolved by adding 1.5 mL of 0.2 mol/L nitric acid. After this treatment, the 113 Cd/ 114 Cd ratio in the soil solution could be measured with high precision, within RSD 5%. The correction of mass bias was not required. The proportion of E-values to total Cd concentration in the soil samples ranged between 50 and 60%. These results indicate that the E-value of Cd in uncontaminated soil can be measured by using both coprecipitation separation and isotope dilution ICP-MS.

Determination of Labile Cadmium in Lime-amended Soils by Isotope Dilution Plasma Mass Spectrometry

“…Fifteen grams of soil were equilibrated with 150 mL of water on a magnetic stirrer for more than 2 d. Then 1.5 mL ARTICLE of enriched 113 Cd (93.29% 113 Cd, 0.46% 114 Cd, 10.96 mmol Cd L À1 ) was added to the suspension and mixed with a stirrer. After exchange times of 1, 4, 10, 40, 100, and 400 minutes, and 1, 4, 7, 11, and 15 days, a 2 mL subsample was collected from the suspensions and the 113 Cd/ 114 Cd ratio was determined by ICP-MS. 4)…”

“…Recently, isotopically exchangeable Cd, or the labile-Cd fraction, in agricultural soils has been evaluated by using the isotope dilution method. 4) We will be able to estimate not only the isotopically exchangeable Cd pool (E-value), [5][6][7] but also the velocity of Cd exchange and instantaneously exchangeable Cd by using the isotope exchange kinetics (IEK) technique. 8) In this study, we exam-ined the effects of soil pH on E-values and IEK parameters in lime-amended soils and upland soils.…”

Assessing the Lability and Environmental Mobility of Organically Bound Copper by Stable Isotope Dilution

“…The isotopic ratio of the postequilibrium solution phase, which is different from both native and spike isotopic ratios (as a result of mixing with the freely exchangeable soil metal fraction), can be assayed by inductively coupled plasma mass spectrometry (ICP-MS). ,− The metal “ E -value” can then be calculated using a simple mathematical expression − The precision and superiority of SID, in comparison to, e.g., chemical fractionation and speciation methods, thus arise from its noninvasive nature and its ability to discriminate between the freely exchangeable and the permanently locked pools of soil metals regardless of their speciation or the soil chemical phase (or functional group) to which they are attached, and with minimum disturbance to the soil natural physicochemical conditions. ,,,, SID approaches have already been verified and successfully applied to estimate the labile pool of various metals in soil, e.g., Pb, Zn, Ni, Cu, Cd, and Hg. ,,− ,− …”