Speciation and Bio-Imaging of Chromium in Taraxacum officinale Using HPLC Post-column ID-ICP-MS, High Resolution MS and Laser Ablation ICP-MS Techniques

Abstract

A new analytical procedure for the speciation of chromium (Cr) in plants by high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) was developed using a strong anion-exchange Mono Q column for the separation of the Cr species. To optimize the analytical procedure, Cr complexes were first synthesized from Cr-nitrate with the addition of an excess of ligand (90°C). Cr-oxalate, Cr-malate, Cr-citrate, Cr-aconitate and Cr-quinate complexes and Cr-nitrate (pH 6.5) were chromatographically separated from Cr(VI) by applying linear gradient elution from 100% water to 100% NH4Cl at a flow rate of 1.5 ml min−1 in 10 min. The column recoveries ranged from 100 to 104%. The exception was Cr-aconitate (column recovery 33%), where a quantitative synthesis was not possible. Good repeatability of the measurements (relative standard deviations better than ± 3%) and low limits of detection (below 0.37 ng ml−1 Cr) were achieved for the individual Cr species. The developed analytical procedure was applied to Cr speciation for dandelions (Taraxacum officinale) grown in soil with a high Cr content and a study of the uptake and metabolism of Cr species in dandelions grown in soil with a low Cr content treated with solutions of Cr(VI) or Cr-nitrate (5000 ng ml−1 Cr, pH 6.5) for 48 h. The separated Cr species were quantified by post-column isotope dilution ICP-MS, while the identification was based on retention times and was also supported by mass spectra obtained with high resolution mass spectrometry (HR-MS). The data indicate that for dandelions grown in Cr-rich soil and that treated with Cr-nitrate (pH 6.5), the Cr was mainly accumulated in the roots, while in plants treated with Cr(VI) (pH 6.5), the Cr was evenly distributed between the roots and the leaves. The Cr species found in dandelion roots and leaves were Cr-aconitate, Cr-malate, and Cr-quinate. The results revealed that Cr(VI) was completely reduced and metabolized to Cr(III) complexes. LA-ICP-MS data showed that the Cr in a leaf of dandelion grown in Cr-rich soil was localized mainly at the apex of the leaf.

Stimulating and toxic effect of chromium on growth and photosynthesis of a marine chlorophyte

“…Such reduction and accumulation of Cr(III) was not found in other nondiatom species, suggesting Cr(VI) was the major species that entered the cells in those phytoplankton (Semeniuk et al ., 2016). The phytoplankton investigated in this study was neither a diatom nor a coccolithophore, and therefore, considering that Cr species were not determined during transmembrane uptake processes in our study, it is more likely that Cr entered the cells as Cr(VI) before its intracellular reduction into Cr(III), as suggested by numerous other studies (Viti et al ., 2014; Zhang et al ., 2019a,b; Marković et al ., 2022).…”

“…Hexavalent and trivalent forms are the most common and stable species of Cr in natural environments (Richard & Bourg, 1991), in which Cr(VI) has very high solubility and bioavailability under toxic conditions (Zhang et al ., 2018a, 2019a,b). When Cr(VI) enters into cells, it reacts spontaneously with the intracellular reductants and generates short‐lived intermediates Cr(V) and/or Cr(IV) that can be ultimately converted to Cr(III) in cells (Viti et al ., 2014; Zhang et al ., 2019a,b; Marković et al ., 2022). In the cytoplasm, some of the Cr(V) that is generated can be re‐oxidised to Cr(VI) producing reactive oxygen species (ROS; Cheung & Gu, 2007).…”

Atomic spectrometry update – a review of advances in environmental analysis

“…Indeed, a Cr VI spike added to basmati rice was reduced to Cr III within 2 h thereby confirming that Cr in rice is present solely as Cr III . An HPLC-ICP-MS method was developed 182 and applied, together with LA-ICP-MS, to study Cr uptake in Taraxacum officinale (dandelion). Two methods for Se speciation analysis, one for rice 150 and the other for plant-based foods, 183 were based on enzymatic extraction and RP IC-ICP-MS. A species-specific ID-GC-ICP-TOF-MS method was developed 184 for the determination of MeHg in canal sediment.…”

Atomic spectrometry update: review of advances in elemental speciation

“…The majority of Cr speciation procedures described in the past year have featured HPLC-ICP-MS . The group of Milacic and Scancar has reported on speciation in wine and beer, 65 speciation and bioimaging in dandelions, 66 the simultaneous speciation of arsenate, chromate, and molybdate in lysimeter water, 67 and the reduction of Cr VI by bacteria in tannery effluent. 68 In each of these studies, Cr speciation was carried out by an HPLC-ICP-MS procedure, originally described in 2012, in which analytes were separated on a SAX fast-protein column (Mono Q HR 5/5) that had been conditioned with 1.0 mol L −1 NaCl.…”

“…Total Cr concentrations, determined by ICP-MS following MAE with HNO 3 and H 2 O 2 , ranged from 1.8 to 22.1 ng mL −1 . For Cr speciation in dandelions, 66 the researchers synthesised a number of complexes with low molecular weight acids (aconitate, citrate, malate, oxalate and quinate) and then identified the species in the plant extracts (water at 70 °C for 6 h) by retention time matching and from the mass spectra obtained (off line) with high resolution ES-MS. Species were quantified by both internal standardisation with Rh and with species-unspecific IDMS with 53 Cr III , both of which were added post-column.…”