a European standard In the standard “EN 16175-2 Sludge, treated biological waste and soil - Determination of mercury - Part 2: Cold vapor atomic fluorescence spectrometry (CV-AFS)”, A method is described for the determination of mercury in aqua regia or nitric acid digests of sludge, treated biological waste and soil obtained using cold vapor atomic fluorescence spectrometry (CV-AVS) according to EN 16173 or EN 16174. The lower working range limit is 0,003 mg/kg (dry matter basis).
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Mono and divalent mercury are reduced to elemental form by tin(II) chloride solution or sodium borohydride in an acid medium. Elemental mercury is stripped from solution in a closed system by means of argon or nitrogen flow. Mercury vapor is injected into the cell of an atomic fluorescence spectrometer, where mercury atoms are excited by radiation of a specific wavelength, usually about 254 nm. The intensity of fluorescence radiation is a function of the mercury concentration. Concentrations are calculated using a calibration curve.
The matrix of the analyzed solution is dominated by the acids used in the digestion step. In this standard, tin(II) chloride is recommended as a reducing agent because sodium borohydride reduces many elements commonly found in soil, sludge and waste extract solutions to the elemental state, which can cause matrix problems under certain conditions. However, it is still possible to use sodium borohydride as a reducing agent. The concentration range of 0,1 µg/l to 10 µg/l in the digested solution can be determined directly, corresponding to 3,0 µg/g to 0,003 µg/g mercury when a 0,3 g sample is digested. Higher concentrations can be determined if the digested solution is diluted. Sensitivity can be increased by the amalgamation technique.
The presence of water vapor or aerosol in the fluorescence cell may cause suppression due to quenching. Water vapor must be removed from the carrier gas stream using a hygroscopic membrane before entering the detector. Noble metals such as gold and silver may combine with mercury and cause suppression. In addition, anions such as sulphur, iodide and bromide, which strongly complex mercury, may also cause suppression.
When tin(II) chloride is used instead of sodium borohydride, less interference from heavy metals occurs. When flow systems are used, the interference effects from heavy metals may be less than those stated in the table given in the standard.
For the determination of trace and ultra-trace levels of mercury, the reagents must be of sufficient purity. The concentration of mercury or interfering substances in the reagents and water must be negligible compared to the lowest concentration to be determined.
The reagents used in this standard include: water, hydrochloric acid, nitric acid, aqua regia, tin(II) chloride solution, sodium borohydride solution, mercury standard stock solution, mercury, standard solution I, mercury, standard solution II, mercury, standard solution III and carrier gas
Test equipment used in these tests includes:
The test solution is a portion of a particle-free digestion or extraction solution prepared according to EN 16173 or EN 16174. To dilute the test solution, 10 ml of the prepared digestion solution is transferred to a 100 ml volumetric flask and filled to the mark with water.
A test blank solution is prepared simultaneously with the extraction of the test sample with aqua regia or nitric acid, following the same procedure, using the same quantities of all reagents for the determination, but omitting the test solution. Transfer 10 ml of the test blank solution to a 100 ml volumetric flask and fill to the mark with water.
When preparing calibration solutions, before each determination batch, prepare a calibration blank solution and at least five calibration solutions covering the concentration range to be determined from the 100 µg/l mercury standard solution III.
Pipette 100 ml, 0 ml, 1 ml, 2 ml, 5 ml and 10 ml of mercury standard solution III into a series of 20 ml volumetric flasks. Fill to the mark with diluted nitric acid solution or diluted aqua regia solution and mix well. These solutions correspond to mercury concentrations of 0 µg/l, 1 µg/l, 2 µg/l, 5 µg/l, 10 µg/l and 20 µg/l, respectively.
When measuring the test sample, the cold vapor generator is connected to the atomic fluorescence spectrometer and the time-controlled measurement program is started. The test blank solution and then each test solution are analyzed and the signals are recorded. If the mercury concentration of the test solution exceeds the calibration range, the test sample solution is diluted with diluted nitric acid solution or diluted aqua regia solution accordingly.
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