david singapore

Dr. Dr. Iulia Gabriela DavidIulia Gabriela David

Department of Analytical Chemistry

Faculty of Chemistry

University of Bucharest,

ROMANIA

KontakTUM Seminar -Singapore 2009

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AIM AIM ---- ---- determination of nature quantity qualitative analysis quantitative analysis

WHATMATTER in

ENVIRONMENTALANALYTICALCHEMISTRY

ENVIRONMENTALANALYTICALCHEMISTRY

HOW MUCH


Manahan Stanley E., Environmental Science, Tehnology and Chemistry, Environmental Chemistry, Boca Raton, CRC Press LLC, 2000

Major aquatic chemical processesMajor aquatic chemical processes


essential elementsessential elements Fe, Se, Cu, Zn Fe, Se, Cu, Zn

toxic metals toxic metals Pb, Cd, Hg, AsPb, Cd, Hg, As


elementsthat occur at very low levelsof a fewppm or less in agiven

system.

Manahan Stanley E., Environmental Science, Tehnology and Chemistry, Environmental Chemistry, Boca Raton, CRC Press LLC, 2000.



Obtain &preserverepresentative

sample

Transform the sample to an analyzable form

Calculate the result

(Input)

(Black box)

(Output)


Pretreatments required for various water samples. Filtration and irradiation steps can be omitted for samples that don’t have particulate matter/significant organic content (e.g., tapwater and open ocean water); this is represented by the dashed line.

A.W.BottVoltam. Determ. of Trace Concentrof Metals in the Environm, Crt.Sep. 14:1 (1995)


SampleSample

Pe

ristaltic pum

p

Carrier flow(HCl)

Reducing agent(NaBH4)

Mixing chamber

Inert gas(Ar)

Gas/liquid separator

Heated Heated quartz quartz

cellcell

Waste

Waste

Hydride(AsH3)

Decte

ctor

SCHEMATIC OF A Hydride Generation-Atomic Absorption Spectrometer

Application: Application: Antimony, arsenic, bismuth, germanium, lead, selenium, tellurium, tin

native3324 8HBOHO3H H BH

O23HA3H3H-33OAnativ6H ss

O23HA343BO3H3

-334AsO H 1543BH

sH

Valve

-high sensitivity

-high sample throughput

-minimal chemical interferences because only few

elements

are able to form hydrides

-enables speciation

-no interferences due to radiation scattering


- limited applicability range

- expensive instrumentation

- relative sensitive to interferences


SCHEMATIC OF AN ICP-AESpectrometer

Nebuliser

Ar

Sample

excited atoms

hDetector

Polychromator

(Ar+sample aerosole)

(T=8000Kh=12 cm)

(cooling, 12 L/min)

(0.8 L/min)

(1 L/min)

(0.002 l/min)

(Frequency 27.12 MHz Power adjustable 800 -1,600 W)

(165–210 nm;210-580 nm)

Plasma torch


-low detection limits for over 70 elements (ppb)

[e.g. 10 ppb for Pb; 50 ppb for As]

-PDA detectors enable simultaneous multielemental analysis

-enables automatisation high sample throughput :

1-3 minutes for a complete analysis of 30 elements

- high Ar consumption-expensive instrumentation


-HMDE-MFE-Bare C, Au, etc.

10-4 -10-5 Hg+2 for co-metal deposition.

A cathodic or reducingpotential is applied for afixed time interval reducing Mn+

Potential is scannedin anodic or oxidizingdirection to strip out Mo


MeASVoltammogram of Cu.

Cu

MeASVoltammograms of Zn, Cd ,Pb).

L.R.=0.1 - 500 μg/LD.L. = 0.05 μg/L (ppb)

Cu

PbZn

Cd

GaL.R.=0.5 - 50 μg/LD.L. = 0.05 μg/L

environmental matrices : -drinking or waste water.samples containing large amounts of chloride (e.g. sea water).


•Sensitive and reproducible (RSD<5%) method for

trace metal ion analysis in aqueous media.

Accuracy is proportionate to the way of sample calibration:<5% when calibrated directly via the method of standard

additions. 10% when a calibration curve is built before measuring20% - 40% when operating uncalibrated

•Concentration limits of detection for many metals are in

the low ppb to high ppt range (S/N=3)

Part per million is instantaneous Part per billion in 20 seconds or less Part per trillion takes 1-3 minutes

compares favorably with AAS or ICP analysis.


•Selectivity & sensitivity can be improved by electrode surface modification e.g.:-Bi deposition on GCE (DL=1.4×10-10 mol/L Pb²+; 0.03 μg/L)

[C. E. Cardoso et.al. Anal. Sci., 23, 1065, 2007]

-Heparin modified GCE (DL= 3×10-10 mol/L Pb²+; 0.06 μg/L) [N.-B. Li, J.-P. Duan, G.-N. Chen, Chin. J. Chem., 22, 553, 2004]

CSV of metal complexes e.g. Zn²+ and Pb²+ with dopamine (DA) from water samples DL=0.5 μg/L Pb²+; 0.06) =1,8 μg/L Zn²+)

Differential pulse voltammograms of a) Blank solution; b) Pb2++Zn2+ (40 ng/ml) without ligand (DA) ; c)Pb2++Zn2+ (40 ng/ml) complexes with DA; Conditions: HMDE, pH, 10; DA= 1.0×10-4 M; accumulation potential, 0.0 V;

accumulation time, 10 s; scan rate, 10 mV/s..

Alireza Asghari , Malaysian J. Anal.Sci.,12(2),410, 2008

•Simultaneous metal ions analysis.No interference between: Lead, Cadmium, Copper and Mercury Zinc, Lead, Cadmium and Mercury Zinc and Copper at low concentrations The method is inherently tolerant of saline solutions: unlike Graphite AA techniques, salinity does not impact the accuracy or performance of the metals measurement

•Inexpensive (field) instrumentation.A quarter of the cost of AA systems A tenth of the cost of ICP systems Use one electrode to measure up to five metals Robust electrodes can make thousands of

measurements



concentrations of the different physicochemical forms of the element (metal ions)

determination

hydrated complexes with

adsorbed on

ligands

inorganicorganic

Colloidal particles

inorganicorganic

As(V) (nontoxic) + As(III) (toxic)

Cu2+ HMDES1 As(III)

reduction

Cu2+ HMDES2 Astotal = As(III)+As(III)reduced

S2-S1 As(V)

inorganic lead and organometallic lead compounds

varying the deposition potential (Ed) in ASV.

Ed=-1.4 V : S1 Et3PbCl+ Et2PbCl2 +Pb(II)

Ed=-0.6 V : S2 Et2PbCl2 +Pb(II)

Complexation Pb(II) +EDTA

S3 Et2PbCl2Ed=-0.6 V :

S1-S2 Et3PbCl

Pb(II) S2-S3



PbH4 A2

inorganic lead [Pb(II) + Pb(IV)]

NaBH4

PbH4 A1 Pb(IV)Pb(IV)oxidation

(NH4)2S2O8

Pb(IV)oxidised + Pb(IV)NaBH4

Pbtotal=Pb(IV)oxidised + Pb(IV)

A2 - A1= Pb(II)Pb(II)

NaBH4

As(III) +As(V)

AsH3A1 As(III)As(III)

1

NaBH4

AsH3 A2

As(V)As(V)2 reduction, KI

As(III) +As(III)reduced

Astotal = As(III) + As(III)reduced

A2 - A1=


Acknowledgement

Financial support is acknowledged from the

PN-II- project BIOXEN 32111-2008.

david singapore

Education

environmental chemistry

elements ppb

waste water

environmental science

gl environmental matrices

various water samples

sea water

gl ppb cu pb zn cd ga