1. Exploring a Combinatorial Approach
Biopolymer Metal Binding and ETV-ICPMS
The Bonded-Phase
Ion-Exchange System
ICP-MS is the cutting edge technology for atomic spectrometry. It can offer part per trillion detection limits, over 5 orders of magnitude of linear response, and works for almost all elements in the periodic table. It uses an inductively coupled plasma (~8,000 K) as the ionization source. Our ICP-MS uses a time of flight system for mass analysis.
Though many labs rely on solution nebulization for sample introduction, this is not always the best technique. It can be problematic for some matrices (e.g. salty solutions, organic solutions, and solids or slurries). An alternative is electrothermal vaporization (ETV). This uses a carbon tube to vaporize the sample before introduction to the ICP-MS. Vaporization temperatures of up to 3,000o C can be achieved in a controlled manner. It can handle a wide variety of sample types, and generally has higher sample introduction efficiency than nebulizers.
Anion Binding Residues
Amino Acid
Cation Binding Residues
CH2 SH
Cysteine CH OH
Tyrosine C O- O
Glutamate
Aspartate N NH
Histidine
Lysine
(CH2)4
NH3+
Other Chelating Residues
NH2
Asparagine HN
Tryptophan
Glutamine
Arginine
(CH2)3
NH2+
H2N
COOH H R
For the past several years, one of the primary focuses of our research group has been the development of novel ion-exchange systems for the purpose of metal remediation from aqueous systems. Expanding on hints from Mother Nature, we chose to explore the metal chelation abilities of proteins and, in particular, their constituent amino acids. In order to simplify these ion-exchange systems, short-chain homopolymers consisting of repeating monomers of a specified amino acid residue have been used. These systems exhibit many of the characteristics for an ideal ion-exchanger – strong binding; fast, efficient release and structural stability. These biologically-based systems also have the added benefit of being environmentally friendly, unlike many traditional exchange systems which require harsh extraction agents.
Sample M+
Support
To ICP-MS
Exploring a Combinatorial Approach
Developing Fluorescence-based Sensors
Creating Chemical-free Remediation Systems
Internal Standards for ICP-TOF-MS
ETV-ICP-MS for Isobars and Isotopes
High throughput screening
Library of
Oligopeptides U
Determine what exclusively binds U
Sequence peptide
CGGDCCGDGC
Synthesize polypeptide(s) and characterize uranium binding +
Exposure to mixed metal solution M Cd Cu
High Throughput Screening of Combinatorial Libraries
High Throughput Screening Techniques
LED - stage illumination
Polycapillary optic/
x-ray source
Si Li detector
Sample
Micro-x-ray-fluorescence (MXRF)
Fluorescence Microscopy
ETV-ICPMS
Bulk screening
Based on fluorescence of bound species
Non-destructive
Single bead screening
Quantitative elemental information
UO22+ in solution
Absorption bands: nm, nm
Emission bands: nm with lmax at 485nm, 510nm, 535nm, and 560nm
Moulin, C. et al. Anal. Chem., 1995, 67,
Bell and Biggers. J. Molec. Spec., 1965, 18,
1mm
Bead in metal solution
Metal-bound bead in acid solution
Metal solution to be quantified
Bind metal
Release metal
Bulk/single bead screening
Applicable for wide range of metals
TackyDot™ slide to array beads
Electrothermal vaporization inductively-coupled plasma mass spectrometry
Column
3-electrode potentiostat
Clean Effluent Stream
Metal Recovery Stream
valve
Reference Electrode
Eapplied
Auxiliary Electrode
An electrical potential is used to change the binding characteristics of the column.
Mn+
Oxidation
Reduction
Free metal can be bound and released by exposing the ligand to successive reduction and oxidation cycles.
Flow
Working Electrodes
Counter Electrodes
Scale up of the electrochemical reactor to practical size requires consideration of materials, geometry, operating conditions, and overall cost.
First Vaporization Stage
Second Vaporization Stage
Resonance energy transfer (RET) can be used to determine various characteristics of metal binding. RET involves the transfer of energy between a fluorescent donor and an acceptor molecule. The efficiency of the energy transfer is dependent on the distance between the molecules, which can be related to their spectroscopic properties.
Graphical Illustration of %RSD
By definition, a small change in the ratio between two elements as a condition changes, is indicative of a good analyte-IS pair. The %RSD of these ratios is used as a quantitative measure of internal standard compatibility.
One problem with ICP-MS is elements of the same nominal mass (isobaric interference). ETV can be used to separate some problematic elements based on their differing volatilities. Rb and Sr can be separated to remove the isobar at mass 87.
Determining the Relationship Between %RSD and Chemical Properties
238U/(IS)
ΔIP
%RSD
r =
Δmass
r = 0.81 A B
Each point on the scatter plots illustrated in the example plot above represents a ratio of 238U and one of approximately 100 IS considered. Analyte-to-IS mass separation typically offered the strongest and most consistent relationship to %RSD for all conditions.
The time of flight design is able to offer excellent isotope ratio precision as a result of simultaneous ion extraction from the plasma. However, difficulties have been encountered with ratio accuracy. Factors that cause this and possible fixes are actively being researched.
Questions? Carina.
Questions? Shelly.
Questions? Ram.
Questions? Haley.
Questions? Adam.
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