Preparative field flow fractionation for complex environmental samples: online detection by inductively coupled plasma mass spectrometry and offline detection by gas chromatography with flame ionization.

Asymmetric flow field flow fractionation (AF4) in particular online with elemental detection via inductively coupled plasma mass spectrometry (ICP-MS) has been developed as powerful and flexible separation technique for suspensions of nano- and micro-particles covering a broad range of applications including environmental water samples and soil extracts. However, for challenging applications, such as particulate phosphorus determination in non-contaminated water samples at levels close to the limit of detection the throughput of the analytical field flow fractionation (FFF) is not sufficient. The same holds true for more specific identification and quantification of black carbon (BC) which needs a subsequent complex multi-step analysis using the well-established benzene polycarboxylic acids (BPCA) method. To overcome these limitations, the performance of a commercially available preparative AF4 channel, which has rarely been applied, yet, was investigated in this study. Using the example of an extract from charcoal spiked soil, method development for the preparative channel was performed and the results from six replicate fractionations with multi-element online detection by ICP-MS were compared to the results from the analytical channel for the same extracts. A similar fractionation pattern was achieved and the quantitative results agreed well for most of the particulate fractions (ratio 1.7 with standard deviation (SD) 0.2 for fraction 1, ratio 0.81 with SD 0.14 for fraction 2 and ratio 1.1 with SD 0.2 for fraction 3). Relative standard deviations were in the range of 9% to 18% for the preparative channel and between 3% and 17% for the analytical channel. Transferability of the separation parameters between both channels is discussed as well as the operational challenges of the preparative channel. As proof of principle, preparative fractionation of an extract from charcoal spiked soil was performed with fraction collection and subsequent quantification of BC via the BPCA method including derivatization, cation exchange pre-cleaning and finally gas chromatographic separation and quantification via flame ionization detection. The results indicated the majority of detected BC in the often so-called dissolved fraction was bound to nanoparticles (48%) and colloids (27%). Only 25% was detected in the cross flow (truly dissolved fraction). This successful example opens new possibilities for hyphenation of FFF separation with multiple detection techniques for improved characterization of particulate matter in challenging applications.

Groundwater controls on colloidal transport in forest stream waters.

Biogeochemical changes of whole catchments may, at least in part, be deduced from changes in stream water composition. We hypothesized that there are seasonal variations of natural nanoparticles (NNP; 1-100 nm) and fine colloids (<300 nm) in stream water, which differ in origin depending on catchment inflow parameters. To test this hypothesis, we assessed the annual dynamics of the elemental composition of NNP and fine colloids in multiple water compartments, namely in stream water, above and below canopy precipitation, groundwater and lateral subsurface flow from the Conventwald catchment, Germany. In doing so, we monitored meteorological and hydrological parameters, total element loads, and analyzed element concentrations of org C, Al, Si, P, Ca, Mn and Fe by Asymmetric Flow Field Flow Fractionation (AF4). The results showed that colloid element concentrations were < 5 µmol/L. Up to an average of 55% (Fe) of total element concentrations were not truly dissolved but bound to NNP and fine colloids. The colloid patterns showed seasonal variability with highest loads in winter. The presence of groundwater-derived colloidal Ca in stream water showed that groundwater mainly fed the streams throughout the whole year. Overall, the results showed that different water compartments vary in the NNP and fine colloidal composition making them a suitable tool to identify the streams NNP and fine colloid sources. Given the completeness of the dataset with respect to NNP and fine colloids in multiple water compartments of a single forest watershed this study adds to the hitherto underexplored role of NNP and fine colloids in natural forest watersheds.

Comparison of aqueous and enzymatic extraction combination with sequential filtration for the profiling of selected trace elements in medicinal plants from Kenya.

This work presents results for the profiling of eight essential elements (Co, Cu, Ni, V, Mo, Mn, Zn and Cr) in aqueous and enzymatic extracts of eight anti-diabetic medicinal plants, used by Traditional Medicine Practitioners from Nyamira County, Kenya determined by ICP-MS. The plants used in the study were Solanum indicum, Plectranthus barbatus, Ultrica dioica, Bidens pilosa, Solanum mauense, Clerodendrum myricoides, Carissa edulis and Aloe vera. A sequential filtration procedure was applied to fractionate the elemental contents of the obtained aqueous extracts into molecular size fractions. The results indicate that the low molecular size species (<3 kDa) were predominant for Mo, Zn, Ni, Co, Mn and Cu, while the moderately large species (10 kDa-0.45 µm) of V were predominant in most of the medicinal plant extracts. In addition enzymatic extraction was compared to aqueous extraction to study the effect of the gastric and intestinal conditions on the release of selected elements from the plants. The amount of the elements extracted by the gastric phase enzymes was higher than the amount extracted by the intestinal phase enzymes. In general, the determined elemental amounts of enzymatic extractions were higher than those of corresponding water extractions for 70% of the elements studied.

Sequential Extraction as Novel Approach to Compare 12 Medicinal Plants From Kenya Regarding Their Potential to Release Chromium, Manganese, Copper, and Zinc.

This study is focusing on a novel approach to screen a large number of medicinal plants from Kenya regarding their contents and availability of selected metals potentially relevant for treatment of diabetes patients. For this purpose, total levels of zinc, chromium, manganese, and copper were determined by flame atomic absorption spectrometry and inductively coupled plasma mass spectrometry as well as BCR sequential extraction to fractionate the elemental species in anti-diabetic medicinal plants collected from five natural locations in two sub counties in Nyamira County, Kenya. Solanum mauense had the highest zinc level of 123.0 ± 3.1 mg/kg while Warburgia ugandensis had the lowest level of 13.9 ± 0.4 mg/kg. The highest level of copper was in Bidens pilosa (29.0 ± 0.6 mg/kg) while the lowest was in Aloe vera (3.0 ± 0.1 mg/kg). Croton macrostachyus had the highest manganese level of 1630 ± 40 mg/kg while Clerodendrum myricoides had the lowest (80.2 ± 1.2 mg/kg). The highest level of chromium was in Solanum mauense (3.20 ± 0.06 mg/kg) while the lowest (0.04 ± 0.01 mg/kg) were in Clerodendrum myricoides and Warburgia ugandesis among the medicinal plants from Nyamira and Borabu, respectively. The levels of the elements were statistically different from that of other elements while the level of a given element was not statistically different in the medicinal plants from the different sub counties. Sequential extraction was performed to determine the solubility and thus estimate the bioavailability of the four investigated essential and potentially therapeutically relevant metals. The results showed that the easily bioavailable fraction (EBF) of chromium, manganese, zinc, and copper ranged from 6.7 to 13.8%, 4.1 to 10%, 2.4 to 10.2%, and 3.2 to 12.0% while the potentially bioavailable fraction (PBF) ranged from 50.1 to 67.6%, 32.2 to 48.7%, 23.0 to 41.1%, and 34.6 to 53.1%, respectively. Bidens pilosa, Croton macrostachyus, Ultrica dioica, and Solanum mauense medicinal plants used to treat diabetes by 80 % of the herbalists in Nyamira County were found to be rich in chromium, manganese, copper, and zinc. The EBF of zinc, manganese, and chromium constitutes adequate amounts recommended for daily intake not exceeding the ADI and delivered a low percentage of RDA when estimating daily intake during therapy from typically applied doses. The plants did not show any significant differences at p < 0.05 in terms of concentrations of the elements between the two study areas though the levels of the different elements were statistically significant. Another major observation was that high total levels of the metals in a given plant did not necessarily translate to high bioavailable levels, and hence the need to determine bioavailable form as it is the one accessible to the patient.

Speciation of Pt(II) and Pt(IV) in spiked extracts from road dust using on-line liquid chromatography-inductively coupled plasma mass spectrometry.

The emission of platinum from automobile catalytic exhaust converters is well known and the accumulation of Pt in road dust has been studied by the analysis of total Pt contents. However, there are few studies on the speciation of the emitted Pt-compounds in the environment. A separation method with HPLC-UV has been developed by Nachtigall et al. [Chromatogr. A 775 (1997) 197] with aqueous standards of Pt(II)- and Pt(IV)-chloro complexes. Due to the limited selectivity and sensitivity of the UV-detection this method is not suitable for Pt-speciation in road dust extracts. Therefore, in this study the method of Nachtigall et al. was modified to realize an on-line coupling to ICP-MS with the advantage of Pt-specific detection. Calibration was performed with aqueous standards and spiked road dust extracts. Calibration curves were linear with low residual standard deviation (1.3-3.1% for the aqueous standards) and approximately 10-times lower detection limits compared to the HPLC-UV-method. Moreover, the stability of the model species was investigated using isocratic as well as gradient separation. Isotopic ratios of 194Pt, 195Pt, 196Pt and 198Pt were determined for quality control. A new mathematical correction method for the HfO-interference on the 195Pt-signal was developed. Additionally, the elution pattern of further elements in the road dust extracts was monitored and total element contents were determined in unspiked road dust extracts.

Identification and quantification of metallothionein isoforms and superoxide dismutase in spiked liver extracts using HPLC-ESI-MS offline coupling and HPLC-ICP-MS online coupling.

A two-dimensional chromatographic method for the characterization of metallothionein isoforms (MT) and superoxide dismutase (SOD) in spiked liver extracts was developed for the optimization of extraction procedures from liver samples. Element-specific detection (ICP-MS) and molecule-specific detection (ESI-MS) were applied for maximum species information. A special focus was laid on the quantitative data evaluation (species stoichiometry, calibration with and without matrix, recovery), which is neglected in most MT/SOD publications with hyphenated techniques. Linearity, precision (residual standard deviation of calibration curves <10%), and detection limits (<0.6 mg L(-1) for MT isoforms and 13 mg L(-1) for SOD) prove the suitability of the method for quantification. An alternative quantification is proposed for the extension towards other lesser or even unknown trace element species, especially the native porcine MT and SOD.

Inert sampling and sample preparation--the influence of oxygen on heavy metal mobility in river sediments.

Two approaches have been used to investigate changes in the nature of metal binding in river sediments caused by atmospheric oxygen. Firstly, non-inert and inert sample preparation were applied, in combination with sequential extraction, to determine for which metals inert sample preparation is necessary for correct determination of metal mobility under environmental conditions. Secondly, the metal contents of sediments sampled before and after a river weir were fractionated by sequential extraction to study the effect of the oxygen impact at the weir on heavy metal mobility in the sediments. Different grain-size fractions from one sample were also extracted, to enable selection of the upper grain-size limit most suitable for answering this analytical question. The results showed the need for the inert sample preparation technique for Cd, Zn, Pb, Mn, and Fe, but not for Co, Ni, Cu, and Cr. No significant change of heavy metal mobility at the weir could be proved, although the mobilization behavior of some elements was different. The optimum upper grain-size limit was 63 microm.