Dj. Sinclair et al., HIGH-RESOLUTION ANALYSIS OF TRACE-ELEMENTS IN CORALS BY LASER-ABLATION ICP-MS, Geochimica et cosmochimica acta, 62(11), 1998, pp. 1889-1901
A method has been developed using laser ablation inductively-coupled p
lasma mass spectrometry (LA-ICP-MS) for rapid high resolution analysis
of B, Mg, Sr, Ba, and U in corals. Corals represent a challenge for a
microbeam technique due to their compositional and structural heterog
eneity, their nonsilicate matrix, and their unusual range of trace ele
ment compositions relative to available standards. The method employs
an argon-fluoride excimer laser (lambda = 193 nm), masked to produce a
beam 600 mu m wide by 20 mu m across to average ablation sampling ove
r a range of structural features. Coral sections are scanned at a cons
tant rate beneath the laser to produce a continuous sampling of the co
ral surface. Sensitivity drift is controlled by careful preconditionin
g of the ICP-MS to carbonate material, and standardisation is carried
out by bracketing each traverse down the coral sample by analyses of a
CaSiO3 glass synthesised from coral powder. The method demonstrates e
xcellent reproducibility of both the shape and magnitude of coralline
trace element profiles, with typical precisions of between 1.0 and 3.7
% based on analysis of the synthetic standard. Accuracy varies between
3.8% for B and 31% for U. Discrepancies are attributed to heterogenei
ties in the: synthetic standard, and matrix differences between the si
licate standard and carbonate sample. The method is demonstrated by an
alysis of a coral collected from Australia's Great Barrier Reef near a
weather station recording in-situ sea-surface-temperature (SST), The
elements B, Mg, Sr, and U show seasonal compositional cycles, and tent
ative calibrations against SST have been derived. Using independent IC
P-MS solution estimates of the coral composition to correct for standa
rdisation uncertainties, the following calibrations have been derived:
B/Ca (mu mol/mol)= 1000 (+/-20) - 20.6 (+/-0.8) x SST Mg/Ca (mmol/mol
)= 0.0 (+/-0.3) + 0.16 (+/-0.01) x SST Sr/Ca (mmol/mol)= 10.8 (+/-0.1)
- 0.070 (+/-0.004)x SST U/Ca (mu mol/mol) = 2.24 (+/-0.07) - 0.046 (/-0.003) x SST1 These calibrations agree with literature within experi
mental errors, except for ME which displays a 35% greater temperature
dependence than reported previously. None of the elements in the coral
appear to be sensitive to decreases in salinity associated with heavy
rainfall in the summer of 1991/1992. Copyright (C) 1998 Elsevier Scie
nce Ltd.