14 Environmental Analysis - Focus on Mercury


of very low mercury concentration. Following capture the mercury can be liberated for detection via heating in an automated furnace.


Sample Preparation


For both CVAAS and CVAFS sample preparation is straight forward, the aim of which is to produce a representative and homogenous sample from which elemental mercury may be liberated in vapour form via reduction. A typical approach to sample preparation is digestion and oxidation followed by a reduction step with the appropriate agents and dilution in preparation for measurement. Some samples, solids for example, my require prior breakdown via strong acid conditions and heating. For each analysis a series of matrix matched blanks and standards are also prepared.


Results and Discussion


We present the data generated from the measurement of three types of environmental sample using CVAAS and CVAFS.


Seawater


Samples of the certified reference material (CRM) Coastal Seawater BCR-579 were digested and oxidised via exposure to 0.1 N potassium bromide/potassium bromate solution followed by reduction with hydroxylamine (12 %). Digested samples were subsequently stored in hydrochloric acid. During analysis the inorganic mercury of the sample was reduced to elemental


mercury for measurement following exposure to stannous chloride (10 %) in hydrochloric acid (7 %). The CRM seawater was then analysed in conjunction with matrix matched blanks and standards. The data generated from the analysis of the seawater (n = 7) is shown in Figure 3. The mean measured concentration of mercury in BCR-579 was 1.78 ng L-1


(% RSD = 8.8 %) which has


good agreement with the target concentration of this CRM of 1.9 ng L-1


± 0.5. Water


Samples of CRM National Institute of Standards and Technology (NIST) Water 1641c were digested and oxidised in the same manner as the CRM seawater as described above followed by the same reduction approach. Samples were similarly stored in hydrochloric acid and analysed in conjunction with matrix matched blanks and standards. The data generated from the analysis of the water samples (n = 7) is shown in Figure 4. The mean measured concentration of mercury in Water 1641c was 1.49 mg L-1


target concentration of 1.47 mg L-1


(% RSD = 1.2 %) which shows good agreement with the ± 0.04.


permanganate. The potassium permanganate of the resulting digest solution was reduced by the addition of hydroxylamine. The resulting solution was then in a position to be analysed, during which inorganic mercury was reduced to elemental mercury via the online addition of stannous chloride (10 %) in hydrochloric acid (7 %). As with the seawater and water analysis described above the CRM soil samples were analysed in conjunction with matrix matched blanks and standards. The data generated from this soil analysis (n = 7) is shown in Figure 5. The mean measured concentration of mercury in this CRM soil was 32.28 mg Kg-1


(%


RSD = 3.88 %) and similarly showed good agreement with the target concentration of 32.6 mg Kg-1


± 1.8.


Figure 5: A graph comparing the measured concentration of NIST 2710 Montana Soil CRM across the seven replicate analyses. The seven measurements all fall very close to the 32.6 mg Kg-1 target concentration of this CRM (which is represented in this graph along the black dashed line) and within the target tolerance of ± 1.8 mg Kg-1 dashed lines).


which is indicated by the two red Conclusions


Figure 4: A graph comparing the measured concentration of the NIST Water 1641c CRM across the seven replicate analyses. The seven measurements all fall very close to the 1.47 mg L-1


target concentration of this CRM (which is


represented in this graph by the black dashed line) and within the target tolerance of ± 0.04 mg L-1


(which is indicated by the two red dashed lines).


Figure 3: A graph comparing the measured mercury concentration of the Coastal Seawater BCR-579 CRM across the seven replicate analyses. The seven measurements all fall very close to the 1.9 ng L-1


target concentration of this CRM


(which is represented in this graph along the black dashed line) and within the target tolerance of ± 0.5 ng L-1


(which is indicated by the two red dashed lines). Soil


Samples of CRM NIST 2710 Montana Soil were digested in aqua regia under heat and subsequently oxidised with potassium


CVAAS and CVAFS provide the analyst with a means of very accurate and precise measurement of mercury from ultra-trace to levels considered abundant in environmental sample types. This ability is considerably beneficial to analytical laboratories and in the monitoring of environmental samples. Considering the toxicity of mercury and its movement throughout the environment the ability to measure ultra-trace levels is just as important as measuring levels that are much higher. CVAAS and CVAFS are therefore ideal tools for environmental monitoring particularly with the preparation of the global legal instrument in mind and the emphasis that this will put on the measurement of mercury in environmental samples and across the wider scientific disciplines.


Accurate Emission Monitoring


of Mercury in the Range of 1 µg/m3 Environnement S.A (France) is pleased to introduce the mercury trap version of the AMESA system. Already MCERTS and TUV certified for continuous dioxin and furan monitoring, the AMESA - M has been adapted for mercury monitoring.


More than 15 years experiences of continuous sampling of Dioxins and Furans (PCDD/PCDF) with the AMESA system were used to design the AMESA M for continuous sampling of mercury, a Sorbent Trap Monitoring System (STMS) according to US EPA Performance Standard 12B.


Exclusive features include: Extracts a part of the flue-gas through a heated sampling probe, Sampling of Mercury on paired sorbent traps (for QA purposes), Fully automatic sampling between 30 minutes and 4 weeks, Remote control by Internet or Intranet with TCP/IP connection, Moisture determination and Easy transfer of the operating data protocol by the use of an USB memory stick.


Reader Reply Card No.


Make Low Level Mercury Sampling a Reality with SilcoNert


Laboratory Testing and field results have proven that SilcoNert 2000 from Silkotek (USA) treated sampling and testing equipment is inert to mercury, mercury species, H2S, mercaptans, and many others.


SilcoNert 2000 is an inert coating that can be applied to the most intricate surfaces while maintaining precise tolerances found in monitoring and instrumentation. SilcoNert 2000 can be applied to most components found in mercury and sulphur sampling systems, including: housings, impingers, tubing, fittings, valves, filters, sample cylinders and storage containers, downhole samplers and flare gas and stack probes.


Reader Reply Card No. IET November / December 2012 45 www.envirotech-online.com Reader Reply Card No. 47 172


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