title: Levels of mineral nutrients in fresh- and frozen bulk hydrated biological specimens: a comparison of EDS data collected in the environmental SEM and a conventional cryo-SEM.
abstract: Energy-dispersive X-ray microanalysis (EDS) was compared in fresh- and frozen bulk hydrated tissues using the Environmental SEM (ESEM) and conventional cryo-SEM, respectively. Analysis of globoid inclusions of Eucalyptus calophylla seed from two soil types demonstrated that higher levels of cations (K, Ca, Mg, Al, Fe, Mn, Cu, Zn) occurred in seeds from soils containing higher levels of Al, while EDS-detectable levels of S and P were dependent upon the techniques utilised. Cumulative changes in ESEM-EDS-detectable levels of S and P were characterized by collecting cumulative spectra from nutrient standards and compared with those for K. Progressive increases in K occurred and were consistent with an enriching effect. Levels of S and P increased during early analysis (40-60 sec live time) and decreased thereafter. The semi-conductive nature of biological samples, the loss of anions and gain of cations from the net negatively-charged electron interaction volume contributed to an electrochemical bias. These local modifications in fluid chemistry were reversible. Dehydration effects also occurred in stable, 'wet' samples. These differences indicated that EDS in ESEM may be limited to cations rather than anions, and that changes in fluid electrochemistry and dehydration may affect the level and distribution of elements.
authors.affiliation: Plant Sciences (Horticulture), University of Western Australia, Nedlands.
authors.forename: L M
authors.initials: LM
authors.lastname: Egerton-Warburton
authors.forename: B J
authors.initials: BJ
authors.lastname: Griffin
mesh_terms: D000838:Anions / Q000032:analysis; D002412:Cations / Q000032:analysis; D003890:Desiccation; D004577:Electron Probe Microanalysis / Q000379:methods*; D005615:Freezing; D002479:Inclusion Bodies / Q000737:chemistry; D008670:Metals / Q000032:analysis*; D012639:Seeds / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013048:Specimen Handling
chemical_list: D000838:Anions; D002412:Cations; D008670:Metals