INTERNATIONAL ATOMIC ENERGY AGENCY DEPARTMENT OF NUCLEAR SCIENCES AND APPLICATIONS MARINE ENVIRONMENT LABORATORIES MONACO

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1 INTENATIONAL ATOMIC ENEG AGENC DEPATMENT OF NUCLEA SCIENCES AND APPLICATIONS MAINE ENVIONMENT LAOATOIES MONACO

2 Deterination of Mercury in Sea Water by using Isotope Dilution High esolution Inductively Coupled Plasa Mass Spectroetry ( ID H ICP- MS) Dr. E. Vassileva IAEA Marine Environent Laboratory

3 Suary Probles with analysis of ercury in sea water at low level Isotope Dilution ICP-MS ethod Assessent of all factors influencing the isotope ratios easureents Modetisation of easureent process Calculation of Cobined uncertainty

4 Introduction National and International onitoring prograes have been assessed word-wide to asses the quality of the arine environent It is essential to ensure that the data produced are of sufficient accuracy, so that results fro different laboratories obtained over a nuber of years can be copared EQS 0.07 ng.kg -1 Hg in sea water This low concentration of Hg typically found in natural water present significant challenge for its accurate deterination

5 What is the proble? 1. Data produced are oceanographically inconsistent 2. Different ethods easuring different fractions of ercury 3. Errors in the quantification of the analytical blank 4. Inaccuracies in syste calibration 5. Coplexity of saple atrix 6. Sound and realistic cobined uncertainty estiation associated with the declared easureent results is nearly always lacking, which akes the coparison of different sets of results difficult ACCUAC OF MEASUEMENT DATA: IT MATTES!

6 Principle of isotope dilution = n( n( Pb) Pb) Saple Enriched spike lend C = C K K K ( 1 ) ( K ) ( i) ( i) ( i) Concentrations derived fro ratios Designated by CCQM* as a priary ethod of easureent *Coité Consultatif pour la Quantité de Matière

7 Priary ethod of easureent A priary ethod of easureent is a ethod having the highest etrological qualities, whose operation can be copletely described and understood, for which a coplete uncertainty stateent canbewritten down intersofsiunits and whose results are accepted without reference to a standard of the quantity and being easured.

8 IDMS as a Priary Method of Measureent Siple, well understood relationship between easurand and influencing quantities ==> easureent result is traceable to SI ==> can lead to sall cobined uncertainty

9 Principle and advantages of IDMS Saple Spike lend Isotope ratios ( 202 Hg/ 202 Hg), not absolute concentrations are easured After the coplete isotopic exchange has taken place, eleental losses do not affect the analytical result An external calibration is not necessary /z A quantitative or reproducible recovery of the eleent is not needed The analytical result is independent of changes in intensity by atrix effects

10 Analytical protocol 20 g sea water is spiked with 0.1 diluted spike solution Hg EM-AE 640 Separation of Hg on inicolun filled with Nobias Chelate PA-1 (ph 2) Elution with 0.05 % βmercaptoethanol in 2% HNO 3 (2 g) Isotope ratios easureent n( 200 Hg)/n( 202 Hg) Mass discriination correction, Procedural blank, Instruental background, Dead tie effects

11 Effect of ph on the collection of eleents fro MQW on Nobias Chelate PA1 120 % Ca Mg K Na Hg ph

12 Nobias Chelate P- A1 resin EDTA and IDA are iobilised on ethacrilate polyer

13 Instruentation High sensitivity Low instruental noise epeatability on I easureent at low resolution is ~0.05% High esolution Sector Field Inductively Coupled Plasa - Mass Spectroeter with Apex saple introduction syste

14 Saple container Mass discriination effects during ICP-MS isotopic easureents The production of a different response for ions of different asses during the instruental step of the easureent process is called ass discriination Saple introduction syste ICP Interface MS Detector n ( ) = = 3/4 n ( ) Ech_ Abs r Ech_ Meas Quid ipact of saple atrix characteristics??? I ( ) r = = 2.95/4 I ( )

15 Correction for ass discriination Measured isotope ratio Ech_ Corr = K IM r Ech_ Mes K IM = r IM Cert IM Mes The EM-AE640 was used for the evaluation of ass discriination correction for the IDMS easured isotope ratios n( 200 Hg)/n( 202 Hg).

16 Ipact of residual salinity on easured I The difference in atrix coposition of the saples and solution used for ass discriination correction leads to error larger than the uncertainty claed on the ratio results IM used for accounting of ass discriination effect were spiked with appropriate aount Ca and Mg in order to avoid any difference in the atrix characteristics

17 Matching the atrix conditions during correction for ass discriination 10 µg g -1 Ca, Mg residual salinity after wash out of the colun several ties with 0.05 M CH 3 COONH rapport (200/202)Hg (5ng/g) rapport (200/202)Hg (5ng/g) Concentration en Ca et Mg en µg/g Concentration en Ca et Mg en µg/g

18 To iniise the blank : Use of high-purity reagents Gold trap on the Ar line Extensive cleaning of lab ware (Kr) and resin All operations with the sea water carried out in a closed syste under lainar clean bench inside a clean roo (class 100) Procedural + Instruental blank 0.06 ± 0.03 ngkg -1 (n=12)

19 External correction - bracketing approach optional bkg K rinse bkg Spl 1 rinse bkg Spl 2 rinse bkg K Measureent sequence easureent of rinse blank (for correction for instruental background ) optional easureent of rinse blank (for high eory effects eleents, large differences in eleent concentration and saple atrix coposition between Spls 1 & 2 etc E) easureent of isotopic reference aterial (for correction for ass discriination effects) easureent of saple rinsing step (no easureent) 180 s 0.05 % βmercaptoehanolin 2% HNO 3

20 Modelization of easureent procedure The analytical procedure is based on isotope dilution ass spectroetry (ID ICP-MS) applied as a priary ethod of easureent. C = C K K K ( 1 ) Correction for ass-discriination effects ( K ( ) ) ( i) ( ) i i K = IM-true / IM-Obs lank corrections C = C n / _ bl bl x Correction for dead-tie effects I _ dt = (1 I I raw raw τ)

21 U associated to (sei) additive corrections applied to isotope signal intensities C = C C = C ( K ( Kdt _ rstd_ dt_ r eas Std_ eas K K bkgr _ bkgr _ Std_ Cert Std_ eas Std_ Cert Std_ eas K in_ r K ( i) ( ) in_ r Std_ eas Std_ eas r i r Std_ eas Std_ eas K ) K ) dt_ r and dt_ r K K bkgr _ K bkgr _ K = r in_ Cert Std_ eas Kin _ rr ( i ) ( i ) rr K dt = 1 ±u c_kdt K bkg = 1 ±u c_kbkg K in = 1 ±u c_kin s.u. on correction for dead tie effects s.u. on correction for instr. background s.u. on correction for isobaric interference ef.: Plasa Source Mass Spectroetry: The New Millenniu, Proceeding of the 7 th Durha Conference, (Ed.) G. Holland and S. Tanner, oyal Society of Cheistry, Cabridge, 2001, pp

22 lank is easured by IDMS lank is easured by external calibration lk lk i i C C C = ) ( ) ( = i i lk C C lk lk lk ) ( ) ( Two way for correction for containation

23 Uncertainty calculations Error propagation using partial differentiation More practical to use nuerical approach Kragten s ethod (Analyst, 1994, 119, 2161) Guidelines provided by ISO Guide for the Expression of Uncertainty in Measureentand Eurache Dedicated software used Uncertainties reported herein with coverage factor k = 2 (i.e. 2 x standard uncertainty)

24 Uncertainty budget for the easureent of Hg in sea water s.u.on correction for instruental background Mass discriination factor Hg in sea water 6.35ng/kg ± 6.80% (k=2) s.u. of spike concentrations.u. of blend isotope ratio easureent s.u. of blank deterination

25 ISO/IEC Validation of ethods Validation is the confiration by exaination and the provision of objective evidence that the particular requireents for a specific intended use are fulfilled [J] Note 2: The techniques used for the deterination of the perforance of a ethod should be one of, or a cobination of, the following: Calibration using reference standards or reference aterials Coparison of results achieved with other ethods Interlaboratory coparisons Systeatic assessent of the factors influencing the results Assessent of the uncertainty of the results based on scientific understanding of the theoretical principles of the ethod and practical experience

26 Validation of the ethod- C 579 Certified value : 1.9 ± 0.5 ngkg -1 (k=2) Obtained in this study value: 1,78 ±0.12 ngkg -1 (k=2) Hg in C ngkg Certified value ID ICP-MS CV-AFS

27 Suary The proposed ethod for deterination of low level Hq in sea water is based on atrix separation and ID ICP MS deterination. ID-ICPMS was applied as priary ethod for the certification of Hg aount content in sea water The optiisation of the factors influencing isotopic ratio easureents has consequences on the final IDMS result and on the U stateent on this value The coprehensive total uncertainty budget is iportant tool to assess the ain potential sources of error and to develop strategies to decrease the uncertainty of a value

28 Thank ou Departent of Nuclear Sciences & Applications