Assessment of the concentration of Cr, Mn and Fe in sediment using laser-induced breakdown spectroscopy

In the present study, laser-induced breakdown spectroscopy (LIBS) has been applied for the determination of levels of Cr, Mn and Fe in sediment samples and the results have been compared with that of flame-atomic absorption spectroscopy (F-AAS). Fourteen sediment samples were collected from Tinishu Akaki River (TAR), Addis Ababa, Ethiopia. Pellets of 24 mm in diameter and 3-5 mm in thickness were prepared using a manual hydraulic press under a pressure of 8000 psi by mixing finely ground sediment samples with boric acid. The concentrations of Cr, Mn and Fe were successfully determined by Q-switched Nd:YAG laser at 1064 nm. Quantification of these metals was conducted against certified reference materials of sediments and soils. The LIBS results for the elements varied from 0.060–0.707 mg/g for Cr, 0.895–3.64 mg/g for Mn and 26.9–71.8 mg/g for Fe. The F-AAS results varied from 0.061–1.37 mg/g for Cr, 1.24–4.46 mg/g for Mn and 49.0–83.3 mg/g for Fe. TAR was found to be heavily polluted with Cr. KEY WORDS: Laser-induced breakdown spectroscopy, Chromium, Manganese, Iron, Sediment, Tinishu Akaki River, Ethiopia Bull. Chem. Soc. Ethiop. 2013, 27(1), 1-13.DOI: http://dx.doi.org/10.4314/bcse.v27i1.

Assessment of levels of V, Cr, Mn, Sr, Cd, Pb and U in bovine meat

Pollution of the environment with heavy metals can be a serious problem. In SouthAfrica, particularly, there are many sources of heavy metals, often due to smelter and mining activities. This has led to toxic metals in the environment that directly affect air, water and food. The presence of heavy metal residues in foodstuffs is potentially hazardous to humans and animals. Heavy metals accumulate in certain organs, particularly in the liver and kidney. The objective of this study was to determine the levels of V, Cr, Mn,Sr, Cd, Pb and U in bovine organs and tissues obtained from polluted areas of North West Province, South Africa. Bovine liver, kidney, muscle, fat and bone samples were freeze-dried, homogenized and mineralized using a microwave-assisted digestion system. The levels were quantified using dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS). A bovine muscle (NIST-RM8414) and bovine liver, reference material (NIST-RM1577b), were also analyzed and results agreed with certified values. The study revealed accumulation of Sr in bone, Cd, Pb and U in kidney and bone, Mn in liver and, V and Cr in kidney tissues of cattle.Tshwane University of Technology (TUT) and National Research Fund (NRF).http://journals.sabinet.co.za/sajchem/nf201

Laser-induced breakdown spectroscopy and inductively coupled plasma-mass spectrometry for determination of Cr in soils from Brits District, South Africa

Laser-induced breakdown spectroscopy (LIBS) is an emerging analytical technique, which can be used to perform elemental analysis of any material, irrespective of its physical state. In this study, the LIBS technique has been applied for quantification of total Cr in soil samples collected from polluted areas of Brits, North West Province, South Africa. A Q-switched neodymium-yttrium aluminium garnet (Nd-YAG) laser (10 Hz, λ = 1064 nm) was employed for generation of a laser-induced plasma on the surface of the soil sample. The atomic emission lines were recorded using an Andor Shamrock SR-303i spectrometer, fitted with an intensified charge-coupled device (ICCD) camera. Detailed investigation of experimental parameters such as gate delay time, gate width and laser pulse energy was conducted. Soil samples were dried, finely ground, sieved and thereafter pelletized before LIBS analysis. Calibration curve for the quantification of Cr was constructed using certified reference materials of soils and sediments. The concentrations of Cr in soil samples varied from 111 to 3180 mg/kg. In order to test the validity of the LIBS results, inductively coupled plasma-mass spectrometry (ICP-MS) was also employed for determination of Cr. The results obtained using LIBS were found to be in good agreement with those of ICP-MS.DOI: http://dx.doi.org/10.4314/bcse.v29i3.

Speciation of chromium in cow’s milk by solid-phase extraction/dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS)

Chromium can act either as an essential micronutrient or a chemical carcinogen, depending on its oxidation state. Of the two most stable chromium oxidation states, Cr(VI) is a known carcinogen, while Cr(III) is an essential element. Determination of total Cr cannot therefore be used to evaluate food safety of dairy products, as speciation is required for accurate assessment of potential toxicity. In this study, total Cr was determined by DRC-ICP-MS after mineralisation of freeze-dried milk samples. Chromabond NH2 ion-exchange columns were used to separate Cr(VI) from Cr(III). During the separation process, Cr(VI) was selectively adsorbed onto the Chromabond NH2 column. The retained Cr(VI) was subsequently eluted with two column volumes of 2 M HNO3 and diluted to a final volume of 10 mL. After separation, the Cr(VI) was quantified by DRC-ICP-MS, using O2 as the reactive gas, to alleviate polyatomic ion interference. An O2 gas flow rate of 0.85 ml/min and a high-pass rejection parameter q (Rpq) = 0.5, provided the best compromise signal-to-noise ratio. The method was validated through determining the recovery in milk samples spiked with Cr(VI). The recoveries were quantitative and ranged from 96.4 to 99.2%. A whole milk powder reference material (NIST SRM 8435) was used to evaluate the accuracy of the total Cr quantification method. The observed value showed concordance with the certified value. The limits of detection (LOD) were 0.091 and 0.085 µg/L for total Cr and Cr(VI), respectively. These findings are important for the determination of maximum residue levels (MRLs) of Cr(VI) in dairy products

A record of 236U content from 1940 to 2012 in a coral core from Europa Island, Mozambique Channel : implications on the pathways of fallout from bomb tests in the Pacific Ocean

Abstract: This is a study on the ratios of 236U/238U in a coral core sampled at Europa Island in the southern Mozambique channel, spanning the period from 1940 through 2012. The primary aim of the work was to obtain a record of variations and trends of these ratios in the local sea water and link them to known nuclear bomb tests (mainly in the Pacific Ocean), fallout from which might have reached this region via the prevailing ocean currents, and assess any significant delays which could characterize ocean currents. Values close to 10-9 for the ratio were obtained on the oldest samples from the core, representing the pre-nuclear test era. This is ca. 2 orders of magnitude higher than published values obtained on Caribbean pre-nuclear coral core, and analyses of a prenuclear standard (Vienna KkU) during this work. This indicates some contamination in the chemical sample preparation. Probably due to this high background, no anomalies were observed prior to 1960 although US nuclear tests were carried out in the 1950’s in the Pacific Proving Grounds of the Marshall Islands, and British tests is south Australia. A single very high value (5.94 ×10-7) obtained for 1988 is believed to result from contamination by a hot particle. Disregarding this, the results obtained show two anomalies that are considered real as they rise and fall over several years. ..M.Sc. (Geology

Raman Chemical Imaging of Chromate Reduction Sites in a Single Bacterium Using Intracellularly Grown Gold Nanoislands

Imaging live molecular events within micro-organisms at single-cell resolution would deliver valuable mechanistic information much needed in understanding key biological processes. We present a surface-enhanced Raman (SERS) chemical imaging strategy as a first step toward exploring the intracellular bioreduction pockets of toxic chromate in Shewanella. In order to achieve this, we take advantage of an innate reductive mechanism in bacteria of reducing gold ions Into intracellular gold nanoislands, which provide the necessary enhancement for SERS imaging. We show that SERS has the sensitivity and selectivity not only to identify but also to differentiate between the two stable valence forms of chromate in cells. The imaging platform was used to understand intracellular metal reduction activities In a ubiquitous metal-reducing organism, Shewanella oneidensis MR-1, by mapping chromate reduction