ISO 12846-2012 pdf download.Water quality – Determination of mercury一Method using atomic absorption spectrometry (AAS) with and without enrichment.
ISO 12846 specifies two methods for the determination of mercury in drinking, surface, ground. rain and waste water after appropriate pre-digestion. For the first method (described in Clause 6), an enrichment step by amalgamation of the Hg on, for example, a gold/platinum adsorber is used. For the method given in Clause 7, the enrichment step is omitted.
The choice of method depends on the equipment available, the matrix and the concentration range of interest. Both methods are suitable for the determination of mercury in water. The method with enrichment (see Clause 6) commonly has a practical working range from 0.01 pg/I to 1 pgll. The mean limit of quantification (LOQ) reported by the participants of the validation trial (see Annex A) was 0,008 pg!l. This information on the LOO gives the user of this International Standard an orientation and does not replace the estimation of performance data based on laboratoryspecifIc data. It has to be considered that it is possible to achieve lower LOOs with specific instrumentation (e.g. single mercury analysers).
The method without enrichment (in Clause 7) commonly has a practical working range starting at 0,05 pg/I. The LOQ reported by the participants of the validation trial (see Annex A) was 0,024 pg/I. It is up to the user, based on the specific application, to decide whether higher concentrations are determined by omitting the enrichment step and/or by diluting the sample(s). The sensitivity of both methods is dependent on the selected operating conditions.
Another possibility for the determination of extremely low Hg concentrations down to 0,002 pg/I without pre-concentration is the application of atomic fluorescence spectrometry (see ISO 17852). Specific atomic- absorption mercury analysers allow determinations down to 0,010 pg/I without pre-concentration.
In general, the determination of trace concentrations of Hg by AAS (or AFS) is dependent on clean operating conditions In the laboratory and on the use of high-purity chemicals with negligible low-Hg blanks.
NOTE This International Standard may be applied to industrial and municipal waste water after an additional digestion step performed under appropriate conditions and after suitable method validation (see 7.4). A potential sample stability issue (mercury loss) for anaerobic reducing industrial effluents has to be considered thoroughly.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 5667-1, Water qualify — Sampling — Part 1: Guidance on the design of sampling programmes and sampling techniques
ISO 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples
ISO 8466-1. Water quality — Calibration and evaluation of analytical methods and estimation of performance characteristics — Part 1: Statistical evaluation of the linear calibration function
ISO 8466-2, Water quality — Calibration and evaluation of analytical methods and estimation of performance characteristics — Part 2: Calibration strategy for non-linear second order calibration functions
3 Principle
Mono- or divalent mercury and organo-mercury compounds as well are converted to divalent mercury by oxidation with KBrO3-KBr and then reduced to the elemental form by tin(ll) chloride in an acid medium.
Elemental mercury is then stripped from the solution with the aid of a stream of inert gas or mercury-free air.
Alternatively, samples may be preserved with dichromateiHNOj and digested under appropriate conditions
(e.g. using potassium permanganate/potassium peroxodisulfate). This technique is not part of this International
Standard and has therefore to be validated appropriately by the user.
If the enrichment step is applied, the mercury (in the form of atomic vapour) is transported in a stream of inert gas with negligible mercury content to a quartz tube with a suitable heating and adsorbent (e.g. gold-platinum gauze) on which the mercury is adsorbed.
Other adsorbents based on the principle of amalgamation are allowed if the user demonstrates fitness for purpose.
The mercury is then released by rapid heating of the adsorbent (desorption at 600 t as a minimum) and further transported in a stream of carrier gas to the absorption cell where the absorbance is measured at 253,7 nm in the radiation beam of an atomic absorption spectrometer. Concentrations are calculated using a calibration curve or using the standard addition method.
If the enrichment step is omitted, the mercury is transported directly into a cuvette. Absorbances are also measured at a wavelength of 253.7 nm.
4 General interferences
With mercury, there is a risk that exchange reactions, that is adsorption and desorption. will occur on the walls of the sampling and reaction vessels. The instructions in 6.2.5.2 should therefore be followed exactly.ISO 12846 pdf download.