Volume 85, Issue 12

The fourth conference of the African Network for Analytical Chemists (SEANAC) took place in Maputo, Mozambique, 8-11 July 2012. The SEANAC conferences are always characterized by pre-symposium workshops that are meant to address various aspects for students. In Maputo, on day one, a workshop on "Sample preparation" was given by Dr. Ron Majors of Agilent Technologies. On day two, Dr. Sharon Neal of the National Science Foundation (USA) gave a workshop on "Writing effective grants". On the same day, Dr. Jean Pemberton of Arizona University (USA) gave a workshop on "The basics of writing a good manuscript" and Dr. Jorge Gardea-Torresdey of Texas University at El Paso (USA) gave a workshop on "How to get published in scientific journals". Five keynote lectures were given: "Electrospun sorbents and colorometric probes", Prof. N. Torto, Rhodes University (South Africa); "Pressurized fluid technology in green analytical chemistry", Prof. Charlotta Turner, Lund University (Sweden); "The speciation of mercury in soil, water and ambient air: Analytical protocols and detection", Prof. Andrew Crouch, University of Witwatersrand (South Africa); "Advances in biological and food sample method development by GCxGC/TOF-MS", Prof. Jean-Marie Dimandja, LECO (USA); and "Use of synchrotron techniques to study the environmental implications of nanoparticles in the environment: The case of terrestrial plants", Prof. Jorge Gardea-Torresdey, University of Texas at El Paso (USA). In the main conference, 5 plenary as well as 40 lectures were presented. The papers published in this issue reflect the main areas of focus at the conference, as they covered aspects of agriculture, environment, health, and emerging applications based on nanotechnology. Nelson Torto Conference Editor

Chromium (Cr) is an important raw material in some chemical industries including paint, pigments, textiles, leather tanning, steel fabrication, electroplating, cement preservation, and canning industries. Once in the environment, Cr exists in various oxidation states depending on pH and concentration. Trivalent [Cr(III)] and hexavalent [Cr(VI)] forms are the most common with Cr(VI) being the most toxic to biota. The review discusses various types of polymeric sorbents that have been prepared for the extraction of Cr(VI) from environmental samples, mostly aqueous samples. Sorbents are categorized into biosorbents, hybrid sorbents, synthetic polymeric, and modified natural polymeric sorbents. Most of the emphasis will be on the advantages and disadvantages of different synthetic polymeric sorbents. Important parameters that define the performance of the sorbents, that is, binding capacity, equilibration time, optimum sample pH, and selectivity, are compared.

Past reports indicate that some nanoparticles (NPs) affect seed germination; however, the biotransformation of metal NPs is still not well understood. This study investigated the toxicity on seed germination/root elongation and the uptake of ZnO NPs and Zn 2+ in alfalfa ( Medicago sativa ), cucumber ( Cucumis sativus ), and tomato ( Solanum lycopersicum ) seedlings. Seeds were treated with ZnO NPs at 0–1600 mg L –1 as well as 0–250 mg L –1 Zn 2+ for comparison purposes. Results showed that at 1600 mg L –1 ZnO NPs, germination in cucumber increased by 10 %, and alfalfa and tomato germination were reduced by 40 and 20 %, respectively. At 250 mg Zn 2+ L –1 , only tomato germination was reduced with respect to controls. The highest Zn content was of 4700 and 3500 mg kg –1 dry weight (DW), for alfalfa seedlings germinated in 1600 mg L –1 ZnO NPs and 250 mg L –1 Zn 2+ , respectively. Bulk X-ray absorption spectroscopy (XAS) results indicated that ZnO NPs were probably biotransformed by plants. The edge energy positions of NP-treated samples were at the same position as Zn(NO 3 ) 2 , which indicated that Zn in all plant species was as Zn(II).

Over the past few decades, in response to growing concerns about the impact of polycyclic aromatic hydrocarbons (PAHs) on human health, a variety of environmental forensics and geochemical techniques have emerged for studying organic pollutants. These techniques include chemical fingerprinting, receptor modeling, and compound-specific stable isotope analysis (CSIA). Chemical fingerprinting methodology involves the use of diagnostic ratios. Receptor modeling techniques include the chemical mass balance (CMB) model and multivariate statistics. Multivariate techniques include factor analysis with multiple linear regression (FA/MLR), positive matrix factorization (PMF), and UNMIX. This article reviews applications of chemical fingerprinting, receptor modeling, and CSIA; comments on their uses; and contrasts the strengths and weaknesses of each methodology.

In this study, near-infrared (NIR) spectroscopy, in combination with chemometrics, was used as a rapid tool for determining if exposure to contamination from mine tailings influences the matrices of the specimens, compared to those from natural populations. Principal component analysis (PCA) plots were made from the chemometric models obtained to establish if season of harvest, geographical origin, and level of soil contamination play a determining role in the chemical profiles of the individual specimens harvested from mine sites or natural populations. The random distribution on PCA score plots corroborated the intraspecies variation of Lippia scaberrima previously observed by gas chromatography-flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS) essential oil profiles. Clustering according to the season and origin of the individual plants confirmed that the geographic location and the season of harvest influence the chemical profiles of L. scaberrima . The NIR data could not be correlated with the level of soil contamination to which the specimens were exposed. The PCA scores and loadings plots obtained from NIR data of Searsia pendulina suggest that the species is tolerant to pollution from mine tailings. Although separation was obtained in a three-component PCA model between specimens sampled during different seasons, some clustering was observed by specimens from the same geographical origin.

In this study, toluene–ethanol mixtures were investigated as chemical modifying agents for pine cone powder (PCP) and the optimum modification ratio determined by measuring the improvement in surface properties of the PCP such as Brunauer–Emmett–Teller (BET) surface area, bulk density, and surface negative charge. The modified adsorbents were then applied for the removal of cesium ions from aqueous solution. The result revealed that the chemically modified PCP had better surface properties than the raw BET surface area, and X-ray diffraction (XRD) spectra revealed that the surface area improved and cellulose crystallinity reduced. Cesium adsorption by the chemically modified PCP was much higher than for the raw PCP. Desorption studies were also performed to evaluate the mechanism of adsorption.

This review article describes analytical chemistry beyond green chemistry and all efforts that contribute to a more sustainable development. A background is given on sustainable development and green chemistry. Examples of “greening” strategies for sample preparation, chromatography, and detection are given. Thereafter, the review discusses how and why a method or a solvent could be claimed as being “green”. Green metrics for analytical chemistry is discussed, including the environment, health, and safety (EHS) index and life cycle assessment (LCA). The choice of solvent and the criteria for a solvent being “green” is also discussed. Finally, sustainable analytical chemistry is described by considering the three important “legs” so as to obtain sustainable development—economic feasibility, societal relevance, and environmental soundness. Hopefully, the review article will stimulate some new perspectives on the difference between greenness and sustainability in analytical chemistry.

A simplified rate model is presented showing that when analytes are determined by atomic spectroscopy first in the absence, and then in the presence, of easily ionizable elements (EIEs) as interferents, the change in collisional radiative recombination activation energy, ∆ E a , is zero when the system conforms to local thermal equilibrium (LTE). ∆ E a values of –7.462, –7.925, and –8.898 eV were obtained when Ca(II), Mg(II), and Sr(II), respectively, were determined by inductively coupled plasma-atomic emission spectrometry (ICP‑AES) in the absence and presence of excess Li, while ∆ E a values of –6.477 and –7.481 eV were obtained when Mg(II) and Sr(II), respectively, were determined in the absence and presence of excess K as interferent. A value of –2.223 eV for ∆ E a was obtained when Mg(I) was determined by air-acetylene flame atomic emission spectrometry (FAES) in the absence and presence of excess K. The data confirm that all the systems studied were not in LTE, and suggest pre-LTE collisional radiative recombination in the absence of the interferent in all cases, and that collisional radiative recombination involving electrons from the interferent can occur from the ambipolar diffusion state or the LTE state. Possible causes for departure from LTE, and a possible collisional radiative recombination mechanism to account for the ∆ E a values obtained, are discussed.

The numerical modeling of Zn II speciation amongst the environmental inorganic ligands Cl – , OH – , CO 3 2– , SO 4 2– , and PO 4 3– requires reliable values for the relevant stability (formation) constants. This paper compiles and provides a critical review of these constants and related thermodynamic data. It recommends values of log 10 β p,q,r ° valid at I m = 0 mol·kg –1 and 25 °C (298.15 K), and reports the empirical reaction ion interaction coefficients, ∆ ε , required to calculate log 10 β p,q,r values at higher ionic strengths using the Brønsted–Guggenheim–Scatchard specific ion interaction theory (SIT). Values for the corresponding reaction enthalpies, ∆ r H , are reported where available. There is scope for additional high-quality measurements for the Zn 2+ + H + + CO 3 2– system and for the Zn 2+ + OH – and Zn 2+ + SO 4 2– systems at I > 0. In acidic and weakly alkaline fresh water systems (pH < 8), in the absence of organic ligands (e.g., humic substances), Zn II speciation is dominated by Zn 2+ (aq). In this respect, Zn II contrasts with Cu II and Pb II (the subjects of earlier reviews in this series) for which carbonato- and hydroxido- complex formation become important at pH > 7. The speciation of Zn II is dominated by ZnCO 3 (aq) only at pH > 8.4. In seawater systems, the speciation at pH = 8.2 is dominated by Zn 2+ (aq) with ZnCl + , Zn(Cl) 2 (aq), ZnCO 3 (aq), and ZnSO 4 (aq) as minor species. This behaviour contrasts with that for Cu II and Pb II for which at the pH of seawater in equilibrium with the atmosphere at 25 °C (log 10 {[H + ]/ c °} ≈ 8.2) the MCO 3 (aq) complex dominates over the MCl n (2– n )+ species. The lower stability of the different complexes of Zn II compared with those of Cu II , Pb II , and Cd II is also illustrated by the percentage of uncomplexed M 2+ in seawater, which is ca. 55, 3, 2, and 3.3 % of [M II ] T , respectively.