Dula Amarasiriwardena

CHARACTERIZATION OF TEN SEQUENTIALLY EXTRACTED HUMIC ACIDS AND A HUMIN FROM A SOIL IN WESTERN MASSACHUSETTS

Humic substances are mixtures of macromolecules with varied structures and chemical compositions that are affected by differences in parental biomaterials and environmental conditions. This study used elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and solid-state 13C nuclear magnetic resonance spectroscopy (NMR) to identify the chemical and structural heterogeneity of 10 humic acids (HAs) and a humin. The HAs were obtained by progressively extracting solution from a soil in western Massachusetts, eight times with 0.1 M Na4P2O7 and two times with 0.1 M NaOH. The humin was the residual fraction after 10 base extractions. As indicated by solid state NMR analysis, the aliphatic carbons (0 ∼ 108 ppm) of the HAs increased gradually from 50% in fraction 1 (F-1) to 62% in fraction 9 (F-9) and 70% for the humin, but the aromatic carbons (108 ∼ 162 ppm) were highest in F-1. The band assigned to aliphatic carbon (2930 cm−1) in the DRIFTS spectra gradually increased with further extractions, and the relative intensity of this peak was the highest in humin. The atomic C/H ratio declined from 1.1 for F-1 to 0.6 for F-10 and the humin, consistent with the spectroscopic analyses. In addition, both elemental and spectroscopic data reveal that the last extracted HA and humin contained relatively lower contents of polar functional groups such as carboxylic and phenolic groups. This study shows significant chemical, structural, and molecular differences among the 10 sequentially extracted HAs and humin, even from a single soil.

Calibration of laser ablation inductively coupled plasma mass spectrometry for quantitative measurements of lead in bone

Lead accumulates in bone over many years or decades. Accordingly, the study of lead in bone is important in determining the fate of ingested lead, the potential for remobilization, and for the application of bone lead measurements as a biomarker of lead exposure. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to measure the spatial distribution of lead in bone on the micrometer scale. In general, LA-ICP-MS studies are somewhat limited by the lack of matrix-matched standards and/or reference materials for calibration and validation purposes. Here we describe the application of pressed pellets prepared from New York State Department of Health candidate Reference Materials for Lead in Bone (levels 1 through 4), to provide a linear calibration for (208)Pb/(43)Ca in the concentration range <1 to 30 μg g(-1). The limit of detection was estimated as 0.2 μg g(-1). The measured lead values for pelletized NIST SRM 1486 Bone Meal and SRM 1400 Bone Ash were in good agreement with certified reference values. Using this approach, we quantitatively measured the spatial distribution of lead in a cross-section of goat metacarpal from a lead-dosed animal. The lead content was spatially variable in the range of 2 to 30 μg g(-1) with a complex distribution. In some sections, lead appeared to be enriched in the center of the bone relative to peripheral areas, indicating preferential accumulation in trabecular (spongy) rather than cortical bone. In addition, there were discrete areas of lead enrichment, or hot spots, of 100 to 200 μm in width.

Flow field-flow fractionation-inductively coupled plasma mass spectrometry for sediment bound trace metal characterization

Coupling the gentle size fractionation capability of flow field-flow fractionation (flow FFF) to a sensitive element detector like inductively coupled plasma mass spectrometry (ICP-MS) facilitates the determination of trace metals bound to various size fractions of colloidal and particulate materials. Organic matter in river sediment core samples was extracted by sodium pyrophosphate, and extracted solutions were introduced into the FFF channel for size separation and subsequently elemental detection by ICP-MS. The distributions of Cu, Fe, Mn, Pb, Sr, Ti and Zn with core depth (0–40 cm) and hydrodynamic diameter are obtained. Most trace metals are bound to the 10–15 cm sediment layer and 2–6 nm (fulvic and humic acids) macromolecules. Crude fulvic and humic acids also were isolated by adjusting the pH of the extracted solutions. Trace metals associated with sediment core samples also were extracted selectively by acetic acid and hydroxylamine hydrochloride to leach exchangeable and reducible fractions, respectively, before sodium pyrophosphate extraction. Results show that Pb is readily exchangeable and Mn is reducible as well as exchangeable, whereas Ti is inert and thought to present as fine colloidal minerals. This study illustrates the range of physicochemical information that can be gained using flow FFF-ICP-MS for environmental investigations.

Microwave-Assisted Vapor-Phase Nitric Acid Digestion of Small Biological Samples for Inductively Coupled Plasma Spectrometry

The applicability of microwave-assisted, vapor-phase nitric acid digestion of small biological samples in closed-vessel microwave systems is examined for the inductively coupled plasma atomic emission spectroscopy (ICP-AES) determination of 10 elements (Al, As, Ca, Cu, Cd, Fe, Mn, Mo, Pb, and Zn). A 1.8 mL quartz sample container geometry was optimized for the successful decomposition of 50 to 90 mg of powdered biological samples. Microwave energy was efficiently coupled by addition of 250 μL of distilled deionized water to the sample. A single microwave-assisted, vapor-phase acid sample digestion was accomplished within 30 min (including cooling time) at ∼1200 psi pressure and 450 W microwave power in a commercial pressurized microwave decomposition (PMD) system. Multiple microwave-assisted, vapor-phase acid digestions were achieved at moderately high pressure (400 to 480 psi) and 230 °C with a second closed-vessel microwave apparatus. The results for 10 elements in biological standard reference materials agree well with the certified values.

Matrix separation by chelation to prepare biological materials for isotopic zinc analysis by inductively coupled plasma mass spectrometry

Following an evaluation of three chelating resins [Chelex-100, poly(dithiocarbamate)(PDTC) and carboxymethylated poly(ethyleneimine)–poly(methylenepolyphenylene) isocyanate (CPPI)], a procedure was established with the last of these for the separation of Zn from biological matrix elements prior to 70Zn: 68Zn isotopic analysis by inductively coupled plasma mass spectrometry (ICP-MS). The method was verified by establishing Zn recoveries and by determining its effectiveness in removing Cl and Na from buffered test solutions. Calcium, Na, and Zn concentration data were determined by inductively coupled plasma atomic emission spectrometry. Chlorine was measured by electrothermal vaporization ICP-MS. The efficacy of the technique was demonstrated by the determination of zinc isotope ratios in bovine milk and human urine. Results compared favourably with those obtained using a previously established extraction procedure.

Evaluation of Laser Ablation Inductively Coupled Plasma Mass Spectrometry for the Quantitative Determination of Lead in Different Parts of Archeological Human Teeth.

ABSTRACT The lead content of teeth or tooth-parts has been used a biomarker of cumulative lead exposure in clinical, epidemiological, environmental, and archaeological studies. Through the application of laser ablation inductively coupled plasma mass spectrometry, a pilot study of the micrometer-scale distribution and quantification of lead was conducted for two human teeth obtained from an archaeological burial site in Manhattan, New York, USA. Lead was highly localized within each tooth, with accumulation in circumpulpal dentine and cementum. The maximum localized lead content in circumpulpal dentine was remarkably high, almost 2000 µg g−1, compared to the mean enamel and dentine content of about 5 µg g−1. The maximum lead content in cementum was approximately 700 µg g−1. The large quantity of cementum found in the teeth suggested that the subjects had hypercementosis (excess cementum formation) of the root, a condition reported to have been prevalent among African-American slave populations. The distribution of lead in these human teeth was remarkably similar to the distribution that we previously reported in the teeth of present-day lead-dosed goats. The data shown demonstrate the feasibility of using laser ablation inductively coupled plasma mass spectrometry to examine lead exposure in archaeological studies.

Spectroscopic Characterization of Fulvic Acid Under Different Cover Crop Systems

Abstract Fulvic acids (FAs) are an important dynamic component of soils that may be affected by soil management. Carbon‐13 cross‐polarization total sideband suppression nuclear magnetic resonance (CP‐TOSS 13C NMR) was used to examine the effect of cover crop systems on the characteristics of fulvic acid fractions. FA was isolated from soils with the following treatments: 1) vetch/rye, 2) rye alone, and 3) check (no cover crops) with varying nitrogen fertilizers. Preliminary NMR results indicate that FA from the rye alone system both with and without nitrogen fertilizers contains less aliphatic carbon (0–108 ppm) than that from the other two treatments. Based on the elemental composition analysis result, C∶N ratio of FA from rye alone cover with or without nitrogen fertilizer is lower than FA from vetch/rye cover system. These data suggest that farming systems affect the FA compositions.