- Measurement of major elements in water (anions and cations)
The levels of major elements (concentrations in the ppm range) in the water are measured in the two SNO Hybam partner laboratories:
- The geochemistry laboratory of the Federal University of the State of Amazonia (UFAM) in Manaus, Brazil.
- The Geosciences Environment Toulouse (GET) laboratory
Inter-calibration tests have been carried out from the outset to check the consistency of the results produced by the two laboratories. The validity of the results for major anions and cations is verified by analysis of certified reference materials: Super-05 and Perade-09 from the National Water Research Institute (Canada).
At UFAM, Manaus, Brazil : analysis of samples from Brazilian stations, representing 9 of the 15 stations in Amazonia.
The anions (F-, Cl-, NO3-, SO42-) were analysed by ion chromatography using the Aquion model (Thermo) equipped with an AS14 anion resin and an ASRS4mm suppressor. A column consisting of a positively charged resin was used to separate the anions. The eluent was 9mM sodium carbonate. Anions are detected by ion chromatography using a conductimeter detector.
The cations (Ca2+, Mg2+, Na+, K+) are analysed by ion chromatography using the Aquion model (Thermo) equipped with a CS12A cation resin and a CDRS4mm suppressor. A column consisting of a negatively charged resin was used to separate the cations. The eluent was 0.02M methanesulphonic acid. The cations are detected by ion chromatography using a conductimeter detector.
Silica Si was measured by ammonium molybdate colorimetry using a UV/visible spectrometer, wavelength 710nm (Thermo).
Alkalinity, HCO3- concentration, is measured by titrimetry using an automatic titrator (Titroline5000).
GET, Toulouse:
The cations (Ca2+, Mg2+, Na+, K+) and silica (Si) are analysed by ICP-OES (Inductively Coupled Plasma – Optic Emission Spectroscopy), Horiba Scientific brand, Ultima Expert model. The method involves ionising the sample by injecting it into an argon plasma induced by a high-frequency generator.
The anions (F–, Cl–, NO3–, SO42-) were analysed by ion chromatography model IC2000 ThermoFisher Scientific, equipped with an AS18 column and an ADRS600 4mm suppressor. The eluent was 30mM KOH.
- Measurement of dissolved organic carbon (DOC)
DOC is measured using the HTCO (High Temperature Catalytic Oxidation) method, TOC 5000 Shimadzu. This method involves passing a sample through a high-temperature furnace (680°C) containing a platinum-enriched oxidation catalyst, where the DOC is broken down into CO2. The combustion product transported by the carrier gas (O2) is then detected by a non-dispersive infrared cell.
- Measurement of particulate organic carbon (COP)
COP has been measured since 2006 at 6 stations (Caracarai, Serrinha, Manacapuru, Obidos, Borba and Itaituba). Analyses are carried out at LEFE, Toulouse, using an elemental organic analyser, model Flash 2000 (ThermoFisher Scientific).
- Trace elements analysis
Trace element levels (concentrations of the order of ppb or less) are measured using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) on a Thermo Scientific iCap TQ triple quadrupole instrument at the Geosciences Environnement Toulouse (GET) laboratory. The elements measured were : Ti, V, Cr, Mn, Co, Ni, Cu, Zn, As, Rb, Zr, Mo, Cd, Ba, Pb, Th, U, Sr, Al, Fe and REE. ICP-MS detection limits are in the range 0.1 to 10 ppt. Measurement uncertainty is 5%. The validity and reproducibility of the results are verified using two certified multi-element solutions: the standard EPOND solution and SLRS-6 river water (nrc-cnrs).
- Total dissolved mercury in river water samples
The mercury present in the water sample is oxidised using bromine chloride, BrCl. The oxidised mercury is then reduced by the addition of tin chloride, SnCl2, to volatile elemental mercury. The elemental mercury is purged with argon and collected on a gold trap. The trap is then heated and the desorbed mercury is measured by cold vapour atomic fluorescence spectrometry (CVAFS). The detection limit is 5pg of HgT and the measurements are validated by analysis of a seawater reference material ERM-CA400.
- Total particulate mercury in suspended solids
HgT analyses on solid samples are performed with an AMA direct mercury analyser which is based on combustion of the sample and pre-concentration by gold trap. The trap is then heated and the desorbed mercury is measured by atomic absorption spectrometry. The detection limit is 0.1ng of HgT, and the measurements are validated by analysis of a NIST 1632d carbon reference material.
- Measurement of the 87Sr/86Sr isotope ratio in water
The 87Sr/86Sr isotope ratio is measured by thermionisation mass spectrometry on a Thermo Scientific TRITON PLUS instrument at the Geosciences Environnement Toulouse (GET) laboratory. After separation and purification of Sr by solid-liquid chromatography on Sr-spec Eichrom ® ion exchange resin, 50-100 mesh (Horwitz et al., 1992), approximately 150 ng of Sr were deposited on a 25 µm thick tungsten filament with Ta2O5 as activator. The filament was then heated to around 3400 mA to obtain a signal of at least 5 V in 88Sr. The 87Sr/86Sr ratio was evaluated by the statistical mean of 150 ratios. The validity and reproducibility of the measurements are assessed by regular testing against a standard, SRM 987.
- Measurement of isotope ratios of Oxygen 18O/16O (d18O) and Hydrogen 2H/1H (dH in water)
The stable isotopes ²H and 18O are analysed using constant flow (MultiFlow-Geo) and isotope ratio mass spectroscopy (CF-IRMS, IsoPrime100) at the SHIVA stable isotope platform at the LEFE laboratory in Toulouse.