On-line microcolumn-based dynamic leaching method for investigation of lead bioaccessibility in shooting range soils.

In this work, a miniaturized flow-through leaching test is presented for rapid screening of potential chemical extractants to explore the bioaccessibility of lead (Pb) in contaminated shooting range soils in Valkeala, Finland. The method combines the versatility of microcolumn-based extraction methods with on-line inductively coupled plasma optical emission spectrometry (ICP OES) analysis for expedient assessment of the magnitude of the bioaccessible pools and the leaching kinetics of lead from polluted soils under variable physicochemical scenarios. Acids and salt solutions were studied as potential extractants. The efficiency of the extractants relative to the initial total amount of lead in the soil sample (509 ± 21 mg/kg) were found to increase in the following order: 0.11 M acetic acid (55%) < 1 M MgCl2 (58%) < 0.1 M NH2OH·HCl (61%) < 0.1 M citric acid (93%) < 0.1 M HCl (96%). The proposed on-line microcolumn-based method was further explored for implementation of the modified BCR (now termed Standards, Measurements and Testing Programme, SM&T) sequential extraction procedure to avail the information about different fractions available in the solid sample, and validated by mass balance calculations. The equivalent sequential procedure in a batch format was then studied and compared against the on-line microcolumn extraction method. The on-line dynamic extraction system presented in this work accepts a substantial amount of sample (2.5 g) as compared to previous flow-through mini-column setups (generally accommodating < 0.25 g of sample), thus maintaining sample representativeness and fostering comprehension of the extraction patterns for non-homogenous soil materials. The use of cotton buds and Teflon membranes and holders in the microcolumn setup facilitates the repeatable flow-through leaching of trace elements and restrict formation of preferential channels. Monitoring of the leachable trace elements in real time delivers detailed insight into the ongoing extraction process and provides a time-saving assessment of potential chemical extractants.

PVC-Based Ion-Selective Electrodes with a Silicone Rubber Outer Coating with Improved Analytical Performance.

An outer layer of pure silicone rubber (SR), i.e. SR without any plasticizer, ionophore, or lipophilic anion, was applied on top of a conventional poly(vinyl chloride) (PVC) based K+-selective membrane in a solid-contact ion-selective electrode (SC-ISE). The influence of the outer SR coating on the analytical performance of the K+-ISEs was studied. The presence of the SR coating did not affect the selectivity of the SC-ISE, indicating that the plasticizer, ionophore, and lipophilic anion are spontaneously distributed from the PVC-based membrane into the SR layer. This was confirmed by electrochemical impedance spectroscopy (EIS). Interestingly, the reproducibility of the standard potential of the conditioned SC-ISE was significantly improved from E0 ± 35.3 mV to E0 ± 3.5 mV simply by adding the SR coating on top of the plasticized PVC based K+-selective membrane. Moreover, the adsorption of bovine serum albumin (BSA) was significantly reduced at the SR coated ion-selective membrane. Thus, the addition of a SR coating on a plasticized PVC ion-selective membrane seems to be a feasible method to improve the analytical performance and to reduce the biofouling of potentiometric ion sensors.