University of North Florida
Browse the Citations
-OR-

Contact Info

Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

View Stuart Chalk's profile on LinkedIn

James A. Holcombe

Abbrev:
Holcombe, J.A.
Other Names:
Address:
Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, TX 78712, USA
Phone:
+1-512-471-5140
Fax:
+1-512-471-0985

Citations 6

"Peak Broadening From An Electrothermal Vaporization Sample Introduction Source Into An Inductively Coupled Plasma"
Spectrochim. Acta B 2001 Volume 56, Issue 8 Pages 1431-1440
John Venable and James A. Holcombe

Abstract: Signal broadening using electrothermal vaporization with inductively coupled mass spectrometry (ETV-ICPMS) occurs at a rate much faster than would be predicted by simple longitudinal diffusion. A Monte Carlo simulation that focused on particle motion within the transport tubing was created to elucidate the causes of this dispersion within ETV-ICPMS. Several parameters, including the diffusion coefficient, tube diameter, transport tube length, and flow rate were varied to discern their role in signal broadening. Using typical instrumental parameters, the parabolic flow profile generated by laminar flow of the carrier gas was shown to be the primary cause of dispersion. Manipulating the aforementioned variables to lessen the effects of laminar flow led to a decrease in dispersion. Conversely, increasing the role of laminar flow promoted broadening. The broadening processes should be applicable to any transient introduction system where material must be transported to a detection system. Due to the difference in the rate of broadening expected for particles of different sizes, the simulation was used to calculate the average size of particles generated in the ETV using different mass amounts of sample. No change in particle size (~1 nm) was seen for mass amounts ranging from 10^-10 000 pg, which suggests that the particle number is increased with increasing sample mass rather than the average particle size. Using this method of determining particle size, it might be possible to further evaluate the mechanisms of physical carrier action.

"Comparison Of Silica-immobilized Poly(L-cysteine) And 8-hydroxyquinoline For Trace Metal Extraction And Recovery"
J. Anal. At. Spectrom. 1999 Volume 14, Issue 8 Pages 1209-1214
Maury Howard, Holly A. Jurbergs and James A. Holcombe

Abstract: Poly(L-cysteine) (PLC) and 8-hydroxyquinoline (8HQ) were immobilized on controlled-pore glass and used in a flow injection system for the separation of Cd, Pb and Cu from synthetic sea-water, Co and Ni matrices as well as CRM sea-water. Both resins allowed for the quantitative recovery of 50 µg L-1 Cd and Pb in synthetic sea-water. However, low recoveries of 2-4% and 40-50% were observed using 8HQ for the separation of 50 µg L-1 Cd and Pb, respectively, from a 10 000-fold excess of Co and Ni, while PLC maintained quantitative recoveries. Neither 8HQ nor PLC showed reproducible or complete recoveries of Cu2+ from the columns using the typical means for stripping (1 M HNO3). Online breakthrough experiments showed that 8HQ had a significant strong binding site capacity for Cd, Pb, Cu, Co and Ni. PLC also had strong sites for Cd, Pb and Cu but showed only weak binding of Co and Ni. The selectivity of PLC against these harder acid metals allowed for quantitative recovery of Cd, Pb and Cu in Co and Ni matrices. Extracting low level spikes of Cd and Pb from CRM sea-water (CASS-1 and NASS-2) tested the application to real samples. Recovery efficiencies of Cd were high for both CRM matrices studied. Pb recovery was good for CASS-1; however, recovery from NASS-2 was unexpectedly low. Mass transfer limitations were observed for both resins in the flow system, resulting in apparent decreased capacities at faster flow rates. Stability constants governing Cd adsorption by PLC and 8HQ were obtained by a non-linear least-squares regression analysis of the Cd binding data and revealed that at least four classes of binding site were present on both resins. Stability constants for the most stable sites were estimated using EDTA or ethylenediamine (en) as competing ligands. 8HQ had no sites that were competitive with EDTA, whereas PLC had an EDTA-competitive site with a stability constant of 1 x 10(13) and a capacity of 1 µmol g-1. Both PLC and 8HQ had sites that were stronger than Cd(en)(2) with estimated stability constants ranging from 10(9) to 10(11). Weaker sites on the resins had stability constants that ranged from 10(4) to 10(6). Cd was used to demonstrate the viability of this method for stability constant determination as it is well characterized for both 8HQ and PLC.
Preconcentration Chelation Column

"Characterization Of Immobilized Poly-L-aspartate As A Metal Chelator"
Environ. Sci. Technol. 1999 Volume 33, Issue 10 Pages 1664-1670
Elizabeth Gutierrez, Thomasin C. Miller, Jose R. Gonzalez-Redondo, and James A. Holcombe

Abstract: Poly-L-aspartic acid (PLAsp), which consists of ~50 Asp residues in a linear polypeptide, was immobilized on controlled pore glass (CPG) and evaluated for its selectivity and binding strength in the complexation of metal ions from aqueous solutions The carboxylate side chain of Asp (pKa 5.4±0.2) is thought to be primarily responsible for chelation of the target metals. Of the several metals evaluated, Eu3+, Ce3+, La3+, Cu2+, and Pb2+ exhibited good binding capacities. Quant. determination of single-element capacities were determined for Cu2+ (12±1 µmol/g PLAsp-CPG) and La3+ (7.1±0.3 µmol/g PLAsp-CPG). Isotherms were constructed from breakthrough curves using a flow injection system. These curves were used to evaluate the effective site capacity and formation constants A combination of moderate and strong binding sites for Pb2+ was detected, while moderate binding of Cd2+ was observed with a minimal number of strong binding sites. Several cations showed little to no binding by PLAsp-CPG (e.g., Na+, Ca2+, Mg2+, Mn2+, Co2+, and Ni2+). Propensity for metal binding seems to follow the trend seen for binding to carboxylates in such ligands as acetate. The polydentate binding available from the polypeptide chain significantly enhanced the binding strength with equilibrium. constants in excess of 108 observed for the strong binding sites. The binding selectivity was complementary, in many cases, with the results previously reported for poly-L-cysteine immobilized on CPG.
Preconcentration Complexation

"Model For Nonequilibrium Binding And Affinity Chromatography: Characterization Of 8-hydroxyquinoline Immobilized On Controlled Pore Glass Using A Flow Injection System With A Packed Microcolumn"
Anal. Chem. 2000 Volume 72, Issue 16 Pages 3927-3933
Maury E. Howard and James A. Holcombe

Abstract: This paper discusses the use of pulse techniques for analysis of zonal elution data for the determination of mass-transfer and axial dispersion constants for porous support materials with adsorption to the surface or to a surface-bonded phase. As an example, this paper considers the case of controlled pore glass (CPG) with a bonded phase that is used with microcolumns and a now injection analysis system, For the CPG, axial dispersion in the form of eddy mixing can be described by l = 0.203, and the overall mass-transfer term, K-OL = 3.9 x 10^-6 cm/s. Additionally an affinity chromatography model was adapted to effectively describe systems employing CPG as the support material through modification of equations describing typical affinity chromatography systems and by inclusion of an axial dispersion term in the calculation of N. This model was used to predict breakthrough curves for cadmium adsorption by 8-hydroxyquinolinol immobilized on CPG packed in microcolumns. In general, the information from the model can be used to extract equilibrium-based constants (binding strengths and site capacities) from a nonequilibrium flow system. The data and model can also be employed in determining the performance for scaled-up extraction systems. The modified model is available in EXCEL spreadsheet format as Supporting Information.

"Comparison Of Immobilized Poly--aspartic Acid And Poly--glutamic Acid For Chelation Of Metal Cations"
Anal. Chim. Acta 2004 Volume 517, Issue 1-2 Pages 187-193
Lisa Malachowski and James A. Holcombe

Abstract: Poly--aspartic acid (PLAsp) and poly--glutamic acid (PLGlu) were individually immobilized onto controlled pore glass (CPG) and compared according to their metal-binding capabilities in a solution of pH 7.0. The metal-binding capacities were calculated through the analysis of breakthrough curves generated by monitoring the metal concentrations on a flow injection-flame atomic absorption system. Capacities for individual metals were comparable and in the order of Cu2+ >> Pb2+ > Ni2+ [ap] Cd2+ > Co2+ > Mn2+ >> Na+. Elemental combustion analysis yielded polymer coverage on the CPG of approximately 4 x 1012 to 5 x 1012 chains/cm2, when average chain lengths were used in the calculations. Formation constants and site capacities of both polymers for Cd2+ were determined through equilibrium and breakthrough studies. The maximum log K values for the strong sites were determined to be ~13 for both PLAsp and for PLGlu. Additionally, the metal selectivity of PLAsp and PLGlu was evaluated when breakthrough curves were run with several metals present in solution at one time. Both polymers showed selectivities in the order of their single metal-binding capacities, i.e., Cu2+ > Pb2+ > Ni2+ [ap] Cd2+. Both polymers exhibited similar binding trends and binding strengths for all of the metals studied. This likely reflects the absence of a predetermined tertiary structure of the polymers on the surface and the relatively high residue-per-metal ratio (~20:1), which places less stringent requirements on the steric hindrance between the side chains and the resultant 'wrapping' of the peptide around the metal.

"Immobilized Poly--histidine For Chelation Of Metal Cations And Metal Oxyanions"
Anal. Chim. Acta 2003 Volume 495, Issue 1-2 Pages 151-163
Lisa Malachowski and James A. Holcombe

Abstract: The biohomopolymer poly--histidine (PLHis) was immobilized onto controlled pore glass (CPG) and its metal binding capabilities evaluated through the use of a flow injection-flame atomic absorption system. The metal binding capability of PLHis-CPG was determined through the analysis of the generated breakthrough curves. The polymer likely coordinates cationic metals through the imidazole side chain (pKa[ap]6) present on each histidine residue with both strong and weak binding sites for Cu2+, Cd2+, Co2+, and Ni2+. Weak to minimal binding was observed for Mn2+, Ca2+, Mg2+, Na+, and Cr3+. The bound metals are quantitatively released from the column with an acid strip. It has also been shown that the protonated imidazole side chain present in acidic solutions is capable of binding metal oxyanions such as chromates, arsenates, and selenites; although oxyanion binding currently exhibits interferences from competing anions in solution, such as sulfate and nitrate. The interference in oxyanion binding is less severe in the presence of chloride, phosphate, and acetate. PLHis-CPG exhibits a capacity of ~30 µmol Cu2+/g CPG in neutral to basic conditions, and a capacity of ~70 µmol Cr(VI)/g CPG, ~4 µmol As(V)/g CPG, and ~4 µmol Se(IV)/g CPG in acidic conditions.