Download Difference between total analysis, fractionation and species

Difference between
total analysis,
fractionation and
speciation
KJM MENA 4010
Module 19
Module plan, Week 1

Thursday October 9th;

Lecture, Auditorium 3, hr. 08:15 – 10:00
• Difference between total analysis, fractionation and species
• The significance of species activities rather than total
concentration in terms of mobility and toxicity
• Chemical analytical speciation and fractionation (Al) methods
• Water sampling from different compartments
of the environment
• Sampling strategies for environmental samples

Field work, Vansjø, hr. 10:00 ~ 17:00
• Visit to Morsa – Vansjø watershed
• Sampling of water samples from tributaries to Vansjø and
Vansjø lake
Module plan, Week 1

Friday, October 10th;

Lecture, Auditorium 3, hr. 08:15 – 09:00
• Important species in natural water samples
• Central equilibriums in natural water samples
• Concentrations and activities

Labwork, hr. 09:15 ~ 17:00
• Sample preparation

Total (S2O8) oxidation, Filtration, UV oxidation
• Analysis of:

pH, Alkalinity, Conductivity, UV/VIS absorbency,
• Presentation of instruments:

Major Anions and Cations on IC, TOC, Al-fractions
Module plan, Week 2
 Thursday,

October 16th;
Lecture, Auditorium 3, hr. 09:15 – 11:00
• Challenges with simultaneous equilibrium
• Speciation programs (MINEQL)

PC lab, hr. 11:15 – 16:00
• Practice in using MINEQL
 Friday,

October 17th
Independent report writing
Total analysis
 Most
standard chemical analytical
methods determine the total
amount (component) of an element
in the sample


AAS, ICP and IC
The sample is typically digested
where all analyte is transferred to its
aqueous form
• Me(H2O)2,4 or 6n+ prior to analysis
What is speciation and fractionation?
 Speciation*
Specific form of an element defined as to
electronic or oxidation state,
complex or molecular structure
and isotopic composition
* D.M. Templeton, F. Ariese, R. Cornelis, L- G. Danielsson, H. Muntau, H.P. Van
Leuwen , and R. Lobinski, Pure Appl. .Chem.,2000, 72, 1453
 Fractionation*
Process of classification of an analyte or a
group of analytes from a certain sample
according to physical (e.g., size, solubility)
or chemical (e.g., bonding, reactivity)
properties
* D.M. Templeton, F. Ariese, R. Cornelis, L- G. Danielsson, H. Muntau, H.P. Van
Leuwen , and R. Lobinski, Pure Appl. .Chem.,2000, 72, 1453.
Why is chemical speciation
important?

Mobility and solubility of a compound depend on
in which form it can exist in solution
 The bioavailability of metals and their
physiological and toxicological effects
depend on the actual species present
– not on the total concentration

Examples:
• Cr (VI) more toxic than Cr (III)
• Organometallic Hg, Pb, and Sn are more toxic than inorganic

Methylmercury (CH3Hg+) is kinetically inert, and readily passes
through cell walls. It is far more toxic than inorganic forms
• Organometallic Al, As and Cu are less toxic than inorganic forms


Inorganic Al are more toxic to aquatic organism
than Al bound to organic ligand
Copper toxicity correlates with free Cu-ion conc.
- has reduced toxicity in the presence of organic matter

Aluminum


Toxicity of Al, and its environmental and
biological effect are associated with the forms
present in aquatic system
In aquatic systems, Al exists mainly as:
• free aqueous Al 3+ , AlOH 2+ , Al(OH)+, Al(OH)3 and Al(OH) 4 –
• AlF 2+ , AlF +2, AlF3,
• monomeric SO4 2– complexes, Al-Org


Al speciation depend on soln. pH & conc. of ligand
Toxicity:
• Al 3+, AlOH 2+, Al(OH)+ (more toxic)
• Al-F and Al-Org (less toxic)
pH dependence on Al speciation
Mineql calculations
[Al] = 1E-5M
[SO4] = 1E-4M
[F-] = 1E-6M
Mobility of metals in soil and soil solution
pH
G.W Brummer In the : Bernhard M, Brickman FE, Sadler PJ (eds) The importance of chemical
“speciation” in environmental process. Springer, Berlin Heidelberg New York, 1986, p 170
The significance of species activities
in terms of mobility

The distribution of an element among different species
profoundly affects its transport by determining such
properties as: charge, solubility, and diffusion coefficient

Charge and oxidation states
• Profoundly affect mobility


E.g. The Fe(II) ion is soluble,
whereas Fe(III) is more prone
to hydrolysis and subsequent precipitation
Inorganic complexes
• Formation of hydroxides
is often a key determinant of element solubility
• Inorganic ligands


E.g. NiCl2 and NiSO4 are water soluble
while NiO and Ni3S2 are highly insoluble in water
Organic complexes
• Macromolecular compounds and complexes

Dissolved natural organic matter (DNOM) complex heavy metals and sorb
organic micro pollutants enhancing thereby solubility and mobility
The significance of species activities
in terms of toxicity

The distribution of an element among different species
profoundly affects its bioavailability by determining such properties as:
Charge, solubility, and diffusion coefficient

Charge and oxidation states
• Profoundly affect toxicity



E.g. Cr(III) is an essential element, but Cr(VI) is genotoxic and carcinogenic
Toxic effect of As and its compound decreases in sequence As (III)>As (V)
Inorganic compounds
• Aqueous species

Heavy metals (Cu2+, Cd2+, Zn2+, Pb2+) are commonly more toxic in their aqueous form
• Inorganic complexes


E.g. Transient polymeric aluminum-hydroxo complexes (Al(OH)3) with high toxicity
Organic complexes
• Organometallic compounds


Hydrophobicity and volatility are important
Bioaccumulation in fatty tissues and penetration of membrane barriers
• E.g. MeHg
• Macromolecular compounds and complexes

Heavy metals and organic micro pollutants bound to DNOM
are generally concidered less toxic.
Effect of a pollutant

Determined by its concentration and
physical, chemical and biological characteristics
of the:
Bio-magnificaton
• Pollutant




Solubility in water and
organic solvent
• Bio-accumulability (Kow)
• Bio-magnification
Degradability, persistence (t½)
Organic complexability (Kex)
Density
• Recipient




Stagnant conditions (redox)
Hardness (Ca+Mg)
pH (speciation)
Humic content
Chemical analytical speciation methods

Isotopic composition


Charge and oxidation states



C. Anodic stripping voltametry on electroactive species
Organometallic compounds


B. Potentiometric determination of the activity of
Free aqueous species
(e.g. ion selective electrodes for Free F, Ca)
Organic complexes


A. Selective organic complexation with
spectrophotometric detection
Separation with HPLC, detection with e.g. ICP
Inorganic compounds and complexes


Mass spectrometry (MS) (e.g. 14C/12C)
D. Separation with GC or HPLC, detection with e.g. ICP
Macromolecular compounds and complexes

Size exclusion, ion-exchange, affinity and reversed phase chromatography
(e.g. P and Al fractionation)
Speciation
Species/element specific techniques
A. Spectroscopy

Less application because of
low sensitivity
 Oxy-anions of Mn, Cr
absorb UV/VIS
 Proxy for Humic substances
 Many species can be determined by
addition of selective color forming
reagents

MnO4-
Molecular Absorption spectrophotometry
(MAS)
• For metal species using chromogenic
reagents

Al-8HQ
Speciation
Species/element specific techniques
B & C. Electro analytical techniques

Ion selective Electrode (ISE)





Detection of free-aqua ions (F-, Cu2+, Cd2+, Pb2+)
Low sensitivity (µmol/L –mmol/L)
Less applicable for the speciation of metals
E.g. Fluoride Selective electrode - Al speciation
Polarographic and Voltametric methods
Differential Pulse Polarography (DPP)


Gives separated signals for free-metal ion and
metal complex
DC- polarography

Can be used to distinguish between red-ox states
Speciation
Species/element specific techniques
D. Separation and detection techniques
Separation
 Chromatography

Liquid chromatography/HPLC
• Size, affinity to mobile/stationary phase

Gas chromatography (GC)
• Volatility
Detection techniques
 Non specific techniques



HPLC: Photometer, Refractometer, Diode-array, Electrochemical
and Conductivity
GC:TCD, FID
Element specific

FAAS , GFAAS, ICP-AES, ICP-MS
Speciation
Separation
- Liquid chromatography-HPLC

Samples introduced to chromatographic column
of stationary phase (SP)
 Mobile phase (MP) pumped through column
 Separation based
on the interaction
of the analyte with
the SP and MP
 Separated speciation:
 inorganic species,
such as cations,
anions (IC)
 metal complexes
 organometallic
compounds
Speciation

Example:
Speciation of mercury in soil and sediment by
selective solvent and acid extraction *
*Y. Han , H. M. Kingston , H. M. Boylan, G. M. M. Rahman, S. Shah, R. C. Richter, D. D.
Link, S. Bhandari, Anal. Bioanal. Chem.,2003, 375,428.
Separation
- Gas chromatography (GC)
 Need
to be Volatile and thermal stable
compounds
 Organometallic species

Volatile species :
• Me2Hg, Me2 Se, Me4Sn, Me3Sb, Tetraalkylated
lead

Non-volatile species after derivatization
Speciation
Problems

Often, chemical species present in a given
sample are not stable enough to be determined
as such

During the measurement process the partitioning of
the element among its species may be changed
• This behavior can be caused by intrinsic properties of
measurement methods that affect the equilibrium between
species


For example a change in pH necessitated by the analytical
procedure
Detection Limit (DL) problems

When you split an analyte at low concentration then
each specie concentration may fall below DL
Solution:
Chemical analytical fractionation

Isolate various classes of species of an element
and determine the sum of its concentrations in each class
Based on
Size
Filtration, size-exclusion chromatography
Affinity
Chromatography
Solubility
Hydrophobicity

By means of
Extraction
Charge
Ion-exchange
Reactivity
Complexation to complexbinder
In some instances, fractionation may be refined by
supplementary speciation analysis.

With further analyses and/or calculations the inorganic fraction
can be subdivided into individual species.
Fractionation
Extraction
 Soil

sample
Leaching method
• Sonication, stirring, shaking or
soxhlet with organic solvent


Sequential Extraction (Tessier)
Supercritical Fluid Extraction (SFE)
 Water


CO2
sample
Solvent extraction
Solid Phase Extraction (SPE)
• Ion exchange resins
Fractionation
Ion exchange resins
for fractionation of metals in water
 Retains:



Labile free aqueous metal ions
Labile inorganic complexes
Labile metal organic complex
 Eluted:

Non-labile metal complexes
(Strong complexes)
Fractionation
Example;
Al fractionation



Fractionation of
Monomeric aluminium
from polymeric forms
is accomplished by
20 sec. complexation
with 8-hydroxyquinoline at pH 8.3 with subsequent
extraction into MIBK organic phase
Organic bound monomeric aluminium is separated from
inorganic aluminium (mainly labile) by trapping the latter
fraction on an Amberlight IR-120 ion exchange column
The Al concentrations in the organic extracts are
determined photometrically
Chemical analytical fractionation;
Shortcomings

The discrimination
inherent in the
method can be more
or less selective but it
is not absolute


Small variations in the
methodical cutoff may
cause significant
variations in the output
I.e. Operationally
defined
Small variations in the cutoff will
often give large variations in the
results
ISE
MAS
MS
Summary
Sampling
Sample prep.
Fractionation
Techniques
Liquid phase
• Organic extraction
• SFE
Solid phase (soil)
• Sequential extraction
• Leaching
Sample prep.
Chemical
Speciation
Techniques
Separation
• HPLC
• GC
Element specific
detection Techniques
• GFAAS
• ICP-AES
• ICP-MS
Water sampling from different
compartments of the environment
Sampling and sample preparation
 Soil





Sample genetic horizons
Drying
Storage
Sieving (2 mm)
Grinding/Homogenizing
 Soil



water
Samples at different soil
genetic horizons
Conservation (biocide, cooling)
Filtration (through 0.45µm filter)
Sample conservation

Content of labile substances in water sample can be altered due to the
chemical, physical, and biological reactions




Best is to analyze immediately upon arrival at lab
Reduce biological activity by:







Nutrients: PO43-, NH4+, NO3-, Silicates
Volatile: HCO3-, - pH at circum neutral pH
Refrigeration –Freezing (hysteresis effect)
Store in dark
Add Biocide HgCl2, Azid (may release nutrients)
Filtering through 0,2um filter
Acid H2SO4
Trace metal concervation : Acidification to pH<2 with HNO3
Special: Hg with Cl
Problem associated with sampling , storage and
sample preparation for speciation/fractionation
 The
procedure should not disturb
the chemical equilibrium between
the different forms of the elements
that exist in a given matrix
 Species transformations stimulated by
change in:

Temperature, light, pH, redox
(in case of liquid samples)
Water sampling equipment

Deposition





Soil water



Bulk precipitation
Wet only
Canopy throughfall
Ground vegetation
throughfall
Percolation lysimeter
Suction lysimeter
Runnoff

V-notch weir
Sampling strategy

Large spatial and
temporal variation

Worst case or
representative

Spatial variation:
• Regional or Hotspots
Temporal variation

Seasonal & Climate

Runoff concentrations of
both solutes and
suspended material show
large variations both over
time and as a function of
discharge.
Discharge and concentration
measured continuously in runoff
water from a small catchment in
Norway and N Sweden
Deelstra et al., 1998, Sampling technique and strategy. In: Measuring
runoff and nutrient losses from agricultural
land in Nordic countries. TemaNord, Nordic Council of Ministers,
1998:575
Point sampling strategies
 Different
water sampling strategies
depending on the objectives of the
measurements.

Study processes
• E.g. event studies

Study of total loss
• Flux dependent sampling

Study of chemical and/or biological conditions
• Time averaged sampling
Point sampling strategies

Point sampling with variable time interval – Episode studies

Rainfall - and snow melt events, which often lead to high soil and
nutrient losses, influence to a high degree the sampling frequency.
• Calculations of soil and nutrient losses based on this method are biased.

Point sampling with fixed time intervals


Volume proportional point sampling


Point sampling is triggered each time a certain volume of water has
passed the monitoring station. In general, load estimates based on this
system leads to an improvement
Flow proportional composite water sampling


The accuracy of the result is strongly dependent on the sampling
frequency
An alternative to point sampling systems is volume proportional mixed
water samples. In this case a small water sample is taken, each time a
preset volume of water has passed the monitoring station
Combined sampling

Sampling systems might be combined so as best to suit its purpose.
• It is assumed that the chemical concentration of runoff water during low flow
periods can be considered constant
Integrated
monitoring
The Vansjø Problem


In 1964 the level of nutrients in
the water course was at
moderate level with an evenly
distributed algae growth
Ten years later the water
course was starting to become
eutrophic with increased algae
growth and an almost doubling
of the levels of nutrients as
well as blossoming of
bluegreen alga.


Bluegreen alga produce toxins
A number of remedial actions
have not given the required
effect.
The Morsa Watershed





698 km2
Forest and agricultural
land
8 communes
Below the marine limit
Drinking water source for
60.000 people