LA-ICP-MS in combination with other imaging techniques might yield additional information on the spatial distribution of elements in samples. An example of multidisciplinary research is given below and was targeted to the development/application of imaging of Hg and Se in plants (maize (Zea mays L.) and sunflower (Helianthus annuus L.) at the macro (organ/tissue) and micro (tissue/cellular) level [1, 2]. For elemental imaging both LA-ICP-MS and synchrotron radiation-based micro-X-ray fluorescence spectrometry (SR-μ-XRF, both high energy [ID22 beamline, ESFR, Grenoble] and low energy [TwinMic, Elettra, Trieste]) techniques were used for fast, low-resolution (> 8 μm) mapping of large areas (≥ 1 mm2) and high-resolution (sub-μm) mapping of small areas (≤ 0.05 mm2), respectively. The plants were grown in hydroponic nutrient solution with 0.8 mg/kg Se(IV)/Se(VI) or in commercial pot substrate amended with 50 mg/kg of HgCl2. Roots and leaves were collected after 3 weeks of growing and subjected to cryo-microtoming to 35 μm thick sections followed by freeze-drying. Figure 1 gives an overview of the workflow related to this research and Figure 2 summarizes the results obtained. The imaging techniques proved to be suitable for localization of Hg and Se in plant tissues, with the understanding that the techniques are complementary, i.e. laser ablation-ICPMS is able to scan large areas of a section with low resolution whereas SR-µ-XRF techniques enable high-resolution imaging of small areas. Furthermore, laser ablation has a much higher sensitivity for Hg, while with SR-µ-XRF techniques it is difficult to reach the sensitivity for mapping of Hg in plant tissues.

Figure 1: Root and leaf cross-sections of maize and sunflower plants grown on substrates with Hg(II) or Se(IV/VI). The coloured frames relate to the areas mapped with the various techniques (blue for laser ablation-ICPMS, read for SR-µ-XRF [high energy] and violet for SR-m-XRF [low energy]).

Spatial distribution of mercury in maize roots

Spatial distribution of selenium in sunflower roots

Spatial distribution of selenium in sunflower leaves

Figure 2: Spatial distribution results obtained for Hg and Se in maize roots and sunflower roots and leaves using LA-ICP-MS and SR-μ-XRF.

References

  1. DEBELJAK, M., ELTEREN, J.T. van, VOGEL-MIKUŠ, K. Development of a 2D laser ablation inductively coupled plasma mass spectrometry mapping procedure for mercury in maize (Zea mays L.) root cross-sections. Analytica chimica acta, ISSN 0003-2670. [Print ed.], 2013, vol. , no. , 8 str., [in press], ilustr., doi: http://dx.doi.org/10.1016/j.aca.2013.05.053.
  2. DEBELJAK, M., ELTEREN, J.T. van, VOGEL-MIKUŠ, K., GIANONCELLI, A., JEZERŠEK, D. Comparison of various spectroscopic imaging techniques for investigation of Hg and Se metabolism in plant tissues. V: Colloquium Spectroscopicum Internationale XXXVIII, June 17 - 20, 2013 Tromsø, Norway. Programme and book of abstracts. Tromsø: [s. n.], 2013, str. 198-199.