Hydrogeochemistry Laboratory

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Summary

Hydrogeochemistry Laboratory provides services in the area of water and sediment chemistry. The laboratory specialises in the analysis of groundwaters, rain water, pore waters (e.g. 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 laboratory manager must be contacted at project planning stage if use of the laboratory facilities is envisaged. This is important to ensure correct procedures for sampling, storage, volume, preservation etc. of the sample and allows proper scheduling and resourcing of the work.

We are also the custodians of a variety of hydrochemical equipment for measurement of unstable parameters in the field – contact the laboratory manager for further details.

Quality of the laboratory’s data is assured by using standard operating procedures and quality control measures which enable the accuracy and precision of the data to be demonstrated.

The analyses include, but are not limited to:

  • pH
  • Specific Electrical Conductivity (SEC)
  • 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 (NOx) and filterable reactive phosphorous (FRP), silicon by direct analysis of waters using colorimetry
  • sequential extraction of phosphorous in sediments
  • extraction of biogenic silicon from 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:

  • 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
  • centrifugation or filtration to remove particulate matter from the water sample before it is analysed. Numerous extraction and digestion techniques are used on sediments to obtain solutions for analysis.

Equipment, capabilities and services

The current capabilities of our analytical equipment are listed below, however many instruments have the potential to determine other parameters. Please talk to the laboratory manager if you do not see the analysis that you require below.

A range of of equipment for basic characterisation parameters.

pH-meters, SEC-meters (specific 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.

This instrument is controlled by a laptop computer onto which is loaded the titration software. The analytical equipment consists of a module which contains the pumping mechanism to accurately dispense the titrant from the glass bottle to the titration cell. A pH probe and the titrant dispensing tube are dipped into the sample to be analysed in the titration vessel.

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

Ion Chromatograph Metrohm Compact Pro (IC)

IC with autosampler, dilution control and software control. It is currently used for anion analysis e.g. F, Cl, Br, NO3, PO4, SO4. Chromatography relies on the different partitioning behaviour of molecules between a 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. Each element is identified based on its rate of elution from the column and the concentration is proportional to electrical conductivity of the eluted solution.

Sub-mg/L detection limits can be achieved dependent on sample type and analytical requirements.

A bench top instrument which consists of two components, an autosampler and a box which houses the pump, and chromatography column which determines the anions in solution

Ion Chromatograph Metrohm Compact Pro (IC)

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

ICP-OES is a multi-element simultaneous technique for elemental analysis of cations (e.g. Na, K, Ca, Mg, Fe, Al, Mn etc.), sulphur, phosphorous and silicon. It is used for the direct analysis of waters and of extractions prepared for the determination of biogenic silicon.The sample is introduced as an aerosol into the inductively coupled plasma, which at its core is 10,000Kelvin. The high temperature of the plasma vaporises the aerosol and excites the atoms to high energy levels. On returning to their ground state the spectrum of wavelengths emitted can be used to identify the element that it originated from.

Detection limits of 0.1 to 0.01mg/L can be achieved dependent on sample type and analytical requirements.

A large and complex analytical instrument with an autosampler to enable unsupervised analysis. The sampler has a probe to transfer the sample to the instrument. Once the sample is aspirated into the plasma, an emission signal is captured by the spectrometer and this is related to the concentration of various elements in solution.

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

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 External site link infra‑red gas analyser. Quantification of data is carried out offline.

The DIC analyser consists of three modules housed in one box about the size of a microwave overn. The modules consist of a syringe mechanism for accurate measurement and mixing of sample and reagent, a phase separator and a LiCor CO2 analyser.

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

Membrane Inlet Mass Spectrometer (MIMS) - currently decommissioned (02/2013) but can be reinstated if required by contacting the laboratory manager

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.

A series of tubes which carry the sample from a sample uptake tube to a water bath, through a liquid nitrogen bath and on to a mass spectrometer for analysis.

Membrane Inlet Mass Spectrometer (MIMS)

Automated colorimeter – segmented flow analysis – Seal Analytical 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 three chemistry manifolds and has been set up for the analysis of total oxidised nitrogen (NO3 + NO2), phosphorous and silicon; this allows for capability to perform the following analyses:

  • total oxidised nitrogen (NOx) 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
  • biogenic silicon determination – using carbonate extraction (NB: this analysis can also be carried out on the ICP-OES).
A series of modular pieces of equipment. On the right hand side is the auotsampler which takes up the sample for analysis. The next module is the pump, which is used to suck up the sample and various reagents, after which the solution stream travels to a chemistry module and finally to the colorimeter

Automated Colorimeter - segmented flow analyser

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 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. Large dynamic range, with detection limits of around 0.05?g/L and an upper limit of linearity of approximately 250?g/L in the extracted solution.
A sturdy small bench top instrument with a digital screen where the data values are displayed.

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

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.

Current capability:

  • Chlorophyll-a and Pheophytin – determined after solvent extraction of sediment or water samples.

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.

A small bench top instrument with a covered sample cell on the left hand side and a digital screen on the right hand side which displays the data values for the sample being analysed.

UV/VIS Spectrometer – Unicam UV-VIS Spectrometer Heλios

Topic contact: labs@ga.gov.au Last updated: January 30, 2014