Automated Sequential Injection-Microcolumn Approach with On-Line Flame Atomic Absorption Spectrometric Detection for Implementing Metal Fractionation Schemes of Homogeneous and Nonhomogeneous Solid Samples of Environmental Interest

Abstract

An automated sequential injection (SI) system incorporating a dual-conical microcolumn is proposed as a versatile approach for the accommodation of both single and sequential extraction schemes for metal fractionation of solid samples of environmental concern. Coupled to flame atomic absorption spectrometric detection and used for the determination of Cu as a model analyte, the potentials of this novel hyphenated approach are demonstrated by the ability of handling up to a 300 mg sample of a nonhomogeneous sewage amended soil (viz., CRM 483). The three steps of the endorsed Standards, Measurements, and Testing sequential extraction method have been also performed in a dynamic fashion and critically compared with the conventional batchwise protocols. The ecotoxicological relevance of the data provided by both methods with different operationally defined conditions is thoroughly discussed. As compared to traditional batch systems, the developed SI assembly offers minimal risks of sample contamination, the absence of metal re-distribution/readsorption, and dramatic saving of operational times (from 16 h to 40-80 min per partitioning step). It readily facilitates the accurate manipulation of the extracting reagents into the flow network and the minute, well-defined injection of the desired leachate volume into the detector. Moreover, highly time-resolved information on the ongoing extraction is given, which is particularly relevant for monitoring fast leaching kinetics, such as those involving strong chelating agents. On-line and off-line (for Cu, Pb, and Zn) single extraction schemes are also proven to constitute attractive alternatives for fast screening of metal pollution in solid samples and for predicting the current, rather than the potential, element bioavailability by the assessment of the readily mobilizable metal forms.

How flow-injection analysis (FIA) over the past 25 years has changed our way of performing chemical analyses

“…And coupled to an on-line detector, it can, via the very small extractant volumes delivered to the detector (of the order of 100-300 µl), yield a very high concentration-time resolution [35] and thus a very detailed insight into extraction behaviour [37] as reflected in the recorded extractograms (Fig. 5).…”

A multisyringe flow-through sequential extraction system for on-line monitoring of orthophosphate in soils and sediments

“…The membrane filters (Fluoropore TM , Millipore, 13 mm diameter with 0.45 and 1.0 µm pore sizes for sediment and soil samples, respectively) used at both ends of the extraction microcolumn allowed solutions and leachates to flow freely through but retained the particulate matter. Solid amounts up to 300 mg can be automatically processed without clogging effects as reported elsewhere [19].…”

“…As a consequence of the development of flow-based extraction approaches, on-line leachate measurements are readily applicable, as deduced from current trends in the field [9, 12-14, 16, 18, 19]. However, most of the works capitalize on hyphenated analytical methods based on coupling of the miniaturizated column extraction manifold to continuously operating atomic spectrometers, such as flame atomic absorption spectrometry, inductively coupled plasma-mass spectrometry or inductively coupled plasma-atomic emission spectrometry, whereby the on-line generated extracts are directly injected into the detection system without any further treatment [9,13,14,16,18,19].…”

Fluidized-bed column method for automatic dynamic extraction and determination of trace element bioaccessibility in highly heterogeneous solid wastes

“…Intensive research in the field of dynamic extraction has been over the past few years devoted to the design of low to moderate pressure flow setups capitalized on the different generations of flow analysis, that is, continuous-flow analysis, flow injection analysis and sequential injection analysis, wherein the amount of solid sample usually loaded into the flow-through container ranged from 5 to 300 mg [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] to prevent excessive backpressure in the flow network. In continuous-flow rotating column-based fractionation assays, larger sample masses have been partitioned, yet the particle size distribution should be carefully controlled (samples are frequently sieved down to 250 m) because of the narrow tubing of the column, usually 1.5 mm i.d.…”

“…The minute quantities of solid samples loaded into the flow assemblies have limited the applicability of flow-based dynamic extraction methods to merely homogeneous solids or materials with a certain degree of heterogeneity but with preliminary sample milling or crushing to assure particle size homogenization, which would inevitably lead to the overestimation of the extractable content of target species because inaccessible phases would become exposed to the extractant [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Evaluation of the actual environmental availability of trace elements in highly heterogeneous raw solid wastes, e.g., municipal solid waste incineration (MSWI) bottom ashes exploiting the aforementioned flow setups would thus be inconceivable as the test portion assayed is to be most likely not representative of the bulk medium.…”