The Inorganic section is capable of a wide variety of metals analysis on aqueous samples, using ICP-MS and ICP-OES, ion chromatography, including ultra-low level analysis for mercury, arsenic and selenium in waters and acid digested materials. Total organic carbon, total nitrogen, alkalinity, phosphates and nutrient analysis are also routinely carried out in this laboratory.
Principal Contacts for Inorganic Analysis:
- Fiona Sturgeon – ICP-OES, ICP-MS
- Susan McIntyre – Ion Chromatography, Mercury Analyser, Hydride Generator, Discrete Analyser
ICP-OES (Perkin Elmer 5300DV)
The Perkin Elmer 5300DV is a dual view Inductively Coupled Plasma – Optical Emission Spectrometer.
Principle
Aqueous samples are made into a fine mist by a peristaltic pump feeding a nebulizer attached to a spray chamber. The mist is entrained into a stream of Argon gas and passed through an Argon plasma where molecules and broken into atoms which are in turn ionised. As the electrons in the ionised elements decay into lower energy levels after passing through the plasma, they emit quanta of energy. The difference in energy between the two levels is directly proportional to the wavelength emitted which is detected by the spectrometer. Different wavelengths are associated with different elements and the intensity of the emission is proportional to the concentration.
Benefits of the ICP-OES over the ICP-MS
ICP-OES is not as sensitive as ICP-MS and as such is used for higher concentration (dirtier) samples. The detector uses light emitted from the plasma rather than entraining ions into the spectrometer and as such doesn’t become dirtier as it runs samples.
What do we use it for?
High concentration elements such as Aluminium, Iron and Calcium in soil samples and drilling fluids such as formate brines.
Contacts: Fiona Sturgeon.
ICP-MS (Agilent 7700)
The Agilent 7700 Inductively Coupled Plasma – Mass Spectrometer (ICP-MS) is one of the most advanced and smallest of its kind in the world.
Principle
Aqueous samples are made into a fine mist by a peristaltic pump feeding a nebulizer attached to a spray chamber. The mist is entrained into a stream of Argon gas and passed through an Argon plasma where molecules and broken into atoms which are in turn ionised. The ions are streamlined into the ion optics by and separated by a mass filter onto an Ion detector. The isotopes of the different elements are determined by their mass/charge ratio.
Benefits of the ICP-MS over the ICP-OES
The ICP-MS can detect elements at typically 3 to 4 orders of magnitude better that an ICP-OES. It can also differentiate between isotopes of elements allowing isotopic ratios to be analysed.
What do we use it for?
Waters and acid digested soils for typically up to 20 elements. This instrument is capable of analysing nearly two thirds of the periodic table and unlike most ICP-MSs is capable of handling high matrix samples, such as undiluted seawater due to its high matrix introduction system where the analyte stream is diluted with extra Argon.
Contacts: Fiona Sturgeon.
Dionex Ion Chromatograph
Principle
The Ion Chromatograph separates polar molecules from a solution by passing it over a stationary phase containing ionic functional groups that interact with ions of opposite charge in the analyte. The instrument here is used for anion determination where the negatively charged ions are attracted a positive charge on the column. An eluent consisting of Sodium Carbonate / Sodium Bicarbonate is passed over the column and molecules are eluted in the order of ion strength with which they are bound to the column. The molecules in the eluent pass through a suppressor where the anions are turned into their respective acids. The acids then pass through a conductivity cell where the measured value is proportional to the concentration of the anion. The time after initial sample injection is a function of the anions interaction with the column.
What do we use it for?
Measuring the anions; F–, Cl–, NO3–, SO42- and Br– in water.
Contacts: Susan McIntyre and Carol Curran
PSA Millennium Merlin Mercury Analyser and PSA Millennium Excalibur Hydride Generator Analyser
Principle
Mercury compounds in solution are reduced by the action of Tin(II) Chloride to elemental Mercury vapour which is purged from the liquid phase with Argon. The cold vapour mercury is atoms are excited by incident radiation from a Mercury lamp at a wavelength of 253.7nm. The mercury ions then re-radiate the absorbed energy as the electrons decay into their original orbits. The emitted light s detected at the same wavelength and is proportional to the concentration of mercury in the sample.
The picture above is of the Merlin Mercury analyser but a similar piece of equipment called the Excalibur, generates metal hydrides which are also detected by atomic fluorescence. Acidified solutions are treated with sodium tetrahydraborate to generate the metal hydride. The hydride and excess hydrogen are swept out of the reaction vessel by argon and into a chemically generated hydrogen flame. The hydrides are atomised and then detected by atomic fluorescence.
The Excalibur can be used for Arsenic (193.7nm), Antimony (217.6nm), Selenium (196.0nm) and Tellurium (214.3nm).
Benefits over the ICP-MS and the ICP-OES
The Atomic Fluorescence techniques described above are many times more labour intensive than ICP-MS or ICP-OES but are capable of detecting several orders of magnitude lower. Typical detection limits are shown in the table below.
| Excalibur/Merlin | ICP-MS | ICP-OES | |
| µg/l | |||
| Hg | 0.002 | 0.1 | 40 |
| As | 0.02 | 0.2 | 50 |
| Se | Yet to be determined | 0.9 | 50 |
What do we use it for?
Ultra low level analysis of Mercury, Arsenic and Selenium in Waters and acid digested material such as soils and biological samples.
Contacts: Susan McIntyre
TOC/TN Analysis
We have two types of TOC analyser. The one shown below is a Shimadzu TOC-VCSH. The other TOC analyser is a OI-Analytical 1010 TOC analyser.
Principle
The Shimadzu analyser oxidises total carbon in a sample to carbon dioxide by heating it to 720°C. The resulting CO2 is dehalogenated and measured in a Non-Dispersive Infra Red detector (NDIR). The intensity of the signal is directly proportional to the concentration of carbon in the sample. Total Inorganic Carbon (TIC) is measured by acidifying the sample with phosphoric acid and measuring the released CO2 in the same way. TOC can be calculated as TC-TIC or alternatively Non-Purgable Organic Carbon (NPOC) is determined by acidifying the sample with hydrochloric acid and sparging with oxygen to remove the inorganic carbon and then analysing as TC. TOC in water samples may be measured either way.
This instrument also analyses Total Nitrogen (TN) by oxidising nitrogen compounds to nitrogen monoxide. The gas is then dried, dehalogenated and analysed by Chemiluminescence.
Highly saline samples are a problem for this instrument because the samples will leave a coating of inorganic matter in the combustion chamber. Samples that will have a high dissolved solid content such as sea waters are analysed using the OI-Analytical instrument where the oxidation stage is carried out chemically rather than by combustion. The OI-Analytical instrument is only capable of carrying out TOC/TIC and not TN.
What do we use them for?
The Shimadzu is used for analysing environmental samples from locks, streams, groundwaters and clean commercial samples. The OI-Analytical is used for more dirty commercial samples or samples that are highly saline.
Contacts: Susan McIntyre and Carol Curran
Skalar
The Skalar San++ Continuous Flow Analyser (CFA) is a colourimetric autoanalyser that can make up to 6 analytical measurements simultaneously. It is routinely used for nutrient analysis: NH4-N, NO3-N, Total Nitrogen, PO4-P, Total Phosphate and DOC of surface waters and also determinand specific analysis of extracts generated in suitable matrices (eg acetic acid or KCl).
Discrete Analysis (Konelab Aqua 20)
The Discrete Analyser is an instrument that employs colourimetric reactions to determine the quantity of determinand present.
Accurate volumes of samples are injected into a one off use vial followed by chilled reagents. The solution is mixed and a colour reaction takes place. The intensity of the colour is directly proportional to the concentration of the determinand in the sample.
What do we use it for?
This instrument is used for the analysis of environmental water samples for Ammoniacal Nitrogen, Total Oxidised Nitrogen (TON), Nitrite, Alkalinity and Phosphate.
Contacts: Susan McIntyre and Carol Curran
