Hydrogeochemistry Laboratory

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Summary
Equipment, Capabilities and Services

Summary

Hydrogeochemistry Laboratory provides services in the area of water and sediment chemistry. The laboratory specialises in analysis of groundwaters, rain water and pore fluids (liquid samples pressed from core samples) and sediments. In contrast to commercial laboratory services, each sample can be treated and analysed individually, depending on its characteristics.

The analyses include:

pH
electrical conductivity (EC)
total alkalinity
anions (F, Cl, Br, NO₃, PO₄, SO₄)
cations (major cations: Ca, Mg, K, Na and selected minor cations)
dissolved inorganic carbon (DIC)
dissolved gases (N₂ and O₂)
total oxidised nitrogen (NO_x) and filterable reactive phosphorous (FRP) by direct analysis of waters
sequential extraction of phosphorous in sediments
chlorophyll-a, phaeophytin and chlorin index in waters and sediments
total dissolved nitrogen.

Sample preparation

A number of techniques are used to prepare samples for analysis. These include:

centrifugation or filtration to remove physical particles from the water sample before it can be analysed using Ion Chromatography and Inductively Coupled Plasma Optical Emission Spectrometery.
pore fluids are obtained by pressing core samples using specialised hydraulic presses developed specifically for this purpose by Geoscience Australia mechanical workshop
saturation extracts are processed where not enough volume is obtained from the pressing technique
numerous extraction and digestion techniques are used on sediments to obtain solutions for analysis

Equipment, Capabilities and Services

Range of wet chemistry instruments like pH-meters, EC-meters (electrical conductivity) and Eh-meters (redox potential).

Automated titrimetry – Metrohm 808 Titrando with 5 and 10mL exchange units

Combined pH measurement and automated potentiometric titration for total alkalinity determinations. A number of methods have been developed to analyse low volume pore waters (2-3mL sample); larger volume groundwaters (25mL); high precision seawater (50mL) with water jacketed titration vessel to maintain titration temperature.

Automated titrimetry – Metrohm 808 Titrando with 5 and 10mL exchange units
© Geoscience Australia

Ion Chromatograph (IC) Dionex-120

IC with automated sample loader and online data processing is used for anion analysis. The instrument utilises chromatography as a separation method. Chromatography relies on different partitioning behaviour of molecules between a flowing mobile phase (eluent) and stationary phase (column packed with resin). Ion chromatography uses ion exchange resins to separate ions based on their interactions with the resin. The element type is determined based on different rate of elution from the column and content is proportional to electrical conductivity of eluted solution.

To obtain reliable results a number of methods with different calibration ranges have been developed for different types of samples. The detection limits of 0.1 to 0.05 mg/L can be achieved for most anions, which is adequate even for analysis of rainwater samples.

Ion Chromatograph Dionex-120 (IC). © Geoscience Australia.

Ion Chromatograph (IC) Dionex-120
© Geoscience Australia

Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES), Varian Vista MPX radial

ICP-OES with automated sample loader and online data processing is used for cation analysis.

The sample is introduced into the plasma, a high electron density and high temperature argon flame, which excites atoms to the high energy levels. When excited atoms return to low energy position, emission rays (spectrum rays) that correspond to the photon wavelength are released and measured by highly precise optical spectrometer. The element type is determined based on the position of the photon rays in the spectrum, and content of each element is determined based on the intensity of the rays.

A number of methods with different calibration ranges have been developed for different types of samples. The detection limits of 0.1 to 0.01 mg/L can be achieved for most cations.

Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES),
Varian Vista MPX radial
© Geoscience Australia

Dissolved Inorganic Carbon (DIC) analyser - Apollo SciTech model AS-C3

The DIC analyser determines the sum of the dissolved inorganic carbon species in solution – carbon dioxide, carbonic acid, bicarbonate anion and carbonate anion. Water samples are filtered (0.45µm) and collected in gas tight glass bottles. Each sample is dosed with a drop of saturated mercuric chloride to inhibit biological activity. Samples are stored in the dark and at room temperature.

Strongly acidic conditions during the analysis drive the equilibrium of all the carbon species in the sample to CO₂. Nitrogen purge gas carries the sample gas stream to a LI-COR infra‑red gas analyser.

Dissolved Inorganic Carbon (DIC) analyser - Apollo SciTech model AS-C3
© Geoscience Australia

Membrane Inlet Mass Spectrometer (MIMS)

The MIMS determines dissolved gasses in water samples using a semipermeable membrane sample introduction system coupled to a high vacuum quadropole mass spectrometer. It is capable of high precision gas measurements at very low concentrations.

The system is set up to determine isotopes at masses 28, 29 and 30 (various combinations of N-14 and N-15 isotopes), 32 (O₂) and 40 (Ar) – quantification is carried out off line. Samples are collected in narrow bore glass tubes with ground glass stoppers and are stored at collection temperature (or slightly lower) in order to prevent degassing of the sample before analysis.

Membrane Inlet Mass Spectrometer (MIMS)
© Geoscience Australia

Automated colorimeter – segmented flow analysis – Bran+Luebbe autoanalyser AA3

The autoanalyser uses the principle of segmented continuous flow analysis for fully automatic analysis of solutions (water samples and extractions) using classical wet-chemistry colorimetric methods. Samples are mixed with reagents in a continuously flowing stream controlled by a high precision pump. The colour developed and detected by the digital colorimeter is either directly or indirectly proportional to the concentration of the element of interest.

The system has two chemistry modules which are currently set up for the analysis of total oxidised nitrogen (NO₃ + NO₂) and phosphorous; this allows for capability to perform the following analyses:

total oxidised nitrogen (NO_x) and filterable reactive phosphorous (FRP) by direct analysis of waters
sequential extraction of phosphorous in sediments – using the modified SEDEX method
total dissolved nitrogen – using persulphate digestion
total dissolved phosphorous – using persulphate digestion

Automated colorimeter – segmented flow analysis – Bran+Luebbe autoanalyser AA3. © Geoscience Australia.

Fluorometer – Turner Designs Model 10-AU-005-CE

The fluorometer is capable of determining various analytes in samples via fluorescence. A fluorescent molecule has the ability to absorb light at one wavelength and almost instantly emit light at a new and longer wavelength. The light emitted is directly proportional to the concentration of the element. Specific wavelength filters are installed that are optimal for the element of interest and minimise interference from other fluorescent materials. All compounds that fluoresce can also be measured by colorimetry (e.g. the UV/VIS spectrometer); however the fluorometer is several orders of magnitude more sensitive and is used where colorimetric methods are not sensitive enough.

Whilst normally used in the laboratory with discrete samples in cuvettes (In vitro) the Turner designs instrument can be set up for continuous flow use (In vivo).

Current capability:

Chlorin Index (a measure of biomass freshness in marine sediments) - determined after solvent extraction of sediment with a calibration range of as low as 0-1µg/L for the extracted solution
Chlorophyll-a and Pheophytin – determined after solvent extraction of sediment or water samples. Large dynamic range, with detection limits of around 0.05µg/L and an upper limit of linearity of approximately 250µg/L in the extracted solution.

Chlorophyll‑a for water samples is collected by filtration of large volumes of water (~5L) through GF/C filters and extraction of the particulate matter on the filter.

Fluorometer – Turner Designs Model 10-AU-005-CE . © Geoscience Australia.

UV/VIS Spectrometer – Unicam UV-VIS Spectrometer Heλios

The spectrometric methods are less sensitive than the fluorometric; larger sample volumes are required to determine the equivalent sample concentration. The UV/VIS spectrometer is used in favour of the fluorometer if high concentrations of the parameter are anticipated.