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Chromium speciation by magnetic solid phase extraction on-line with inductively coupled plasma optical emission spectrometry


As a consequence of its industrial application and its natural occurence, both natural and anthropogenic chromium enter into the food chain through water, soil and air. The two species determined to be chemically stable are Cr(III) and Cr(VI), and therefore, both species naturally occur in the environment. While chromium is considered to play a helpful role in the carbohydride metabolism in its trivalent form, the hexavalent species is classified as genotoxic and carcinogenic. World regulatory agencies strictly recommend maximum tolerable limits for chromium in drinking water globally.  Because of the important difference in toxicity of the two species, the need for chromium speciation analysis rather than the determination of the total Cr concentration is of paramount importance. In general the most often applied atomic spectrometric techniques applied for the determination of chromium have to be coupled with a separation technique for the differentiation of the two species.  Such combined techniques can be realized eiher by on-line or off-line coupling. Since the monitoring of harmful species in the environment rquires the processing of many samples to accurately characterize their abundance, automated and uncomplicated methods with high sample throughput are favoured. Apart from chromatographic separation techniques, non-chromatic techniques such as liquid-liquid extraction, capillary microextraction, cloud point extraction and solid phase extraction have been proposed. Flow injection manifolds have often been used to automate such techniques and to interface them to the detection system.

The new method:
A group of Spanish researchers do propose to use a magnetic graphene oxide functionalized with 4-aminobenzenesulfonic acid as a sorbent material for the preconcentration and separation of chromium species. A flow injection manifold was designed, having two collection channels with the sorbent material inside a tubing wrapped around a Nd/Fe/B toroidal magnet and kept in place by polyethylene frits a both ends of the tube. The two collection channels were placed on a eight-port  rotary valve of the flow injection system. Pumping water samples adjusted to pH =3 through the collection channels, both Cr(III) and Cr(VI) analyte species are retained on the sorbent material.

Following collection of the chromium from the water sample, the collection channel is purged by pure water. After such cleaning step, the retained Cr(VI) is eluted from the collection channel by using 3.2% NH4OH solution and is directly send to the sample introduction system of the ICP-AES. During the same time the second collection channel is loaded with the water sample. Again the channel is puged for washing out any remain ing matrix with pure water. Following the cleaning step, elution of this channel is done with 2.3% HNO3, so that total chromium is send to the ICP-AES.

The whole procedure was optimized with respect to collection pH, eluent concentration, FIAS and ICP-AES parameters. Using the optimized conditions and a loading time of 3 min., preconcentration factors of 15 and 23 for Cr(VI and Cr(total) were obtained, leading to detection limits in the order of 0.1 µg/L. A complete cycle of the FI-operation was about 480 s per sample allowing for about 7.5 samples per hour.  

The method was validated by using two certified reference materials and applied for the analysis of different water samples, including seawater and tap water. Also spike recoveries for all water samples were close to 100%.

The original publication

I. Morales-Benítez, P. Montoro-Leal, J.C. García-Mesa, M.M. López Guerrero, E. Vereda Alonso, New magnetic chelating sorbent for chromium speciation by magnetic solid phase extraction on-line with inductively coupled plasma optical emission spectrometry, Talanta 256 (2023) 124262. DOI: 10.1016/j.talanta.2023.124262


Related studies

J.S. Cang, W.X. Gu, Y.H. Zhu, X.S. Zhu, Fe3O4–SiO2–graphene oxide–amino acid ionic liquid magnetic solid-phase extraction combined with inductively coupled plasma optical emission spectrometry for speciation of Cr(III) and Cr(VI) in environmental water, New J. Chem. 46 (2022) 3178–3184. DOI: 10.1039/d1nj04917h

A. Islam, H. Ahmad, N. Zaidi, S. Kumar, A graphene oxide decorated with triethylene-tetramine-modified magnetite for separation of chromium species prior to their sequential speciation and determination via FAAS, Microchim, Acta, 183 (2016) 289–296. DOI: 10.1007/s00604-015-1641-2. DOI: 10.1007/s00604-015-1641-2

K.M. Diniz, C.R.T. Tarley, Speciation analysis of chromium in water samples through sequential combination of dispersive magnetic solid phase extraction using mesoporous amino-functionalized Fe3O4/SiO2 nanoparticles and cloud point extraction, Microchem. J., 123 (2015) 185–195. DOI: 10.1016/j.microc.2015.06.011

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V.N. Alves, N.M.M. Coelho, Selective extraction and preconcentration of chromium using Moringa oleifera husks as biosorbent and flame atomic absorption spectrometry, Microchem. J. 109 (2013) 16–22. DOI: 10.1016/j.microc.2012.05.030.

M.A. Chamjangali, N. Goudarzi, M. Mirheidari, B. Bahramian, Sequential eluent injection technique as a new approach for the on-line enrichment and speciation of Cr(III) and Cr(VI) species on a single column with FAAS detection, J. Hazard Mater. 192 (2011) 813–821. DOI: 10.1016/j.jhazmat.2011.05.095

C.R.T. Tarley, G.F. Lima, D.R. Nascimento, A.R.S. Assis, E.S. Ribeiro, K.M. Diniz, Novel on-line sequential preconcentration system of Cr(III) and Cr(VI) hyphenated with flame atomic absorption spectrometry exploiting sorbents based on chemically modified silica, Talanta 100 (2012) 71–79. DOI:  10.1016/j.talanta.2012.08.023

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K. Saygi, M. Tuzen, M. Soylak, L. Elci, Chromium speciation by solid phase extraction on Dowex M 4195 chelating resin and determination by atomic absorption spectrometry, J. Hazard Mater., 153 (2008) 1009–1114. DOI: 10.1016/j.jhazmat.2007.09.051.

A. Aparna, M. Sumithra, G. Venkateswarlu, A.C. Sahayam, S.C. Chaurasia, T. Mukherjee, Speciation of Cr(III) and Cr(VI) in Seawater after Separation with a Sulphate-form of DOWEX-1 and ETAAS Determination, At. Spectrosc., 27 (2006) 123–127.

T. Sumida, T. Ikenoue, K. Hamada, A. Sabarudin, M. Oshima, S. Motomizu, On-line preconcentration using dual mini-columns for the speciation of chromium(III) and chromium(VI) and its application to water samples as studied by inductively coupled plasma-atomic emission spectrometry, Talanta, 68 (2005) 388–393. DOI: 10.1016/j.talanta.2005.08.064

P. Liang, T. Shi, H. Lu, Z. Jiang, B. Hu, Speciation of Cr(III) and Cr(VI) by nanometer titanium dioxide micro-column and inductively coupled plasma atomic emission spectrometry, Spectrochim. Acta Part B, 58 (2003) 1709–1714. DOI: 10.1016/S0584-8547(03)00136-8.

A. Tunçeli, Speciation of Cr(III) and Cr(VI) in Water after Preconcentration of its 1,5-diphenylcarbazone Complex on Amberlite XAD-16 Resin and Determination by FAAS, Talanta, 57 (2002) 1199-1204. DOI: 10.1016/S0039-9140(02)00237-0

I. Narin, M. Soylak, K. Kayakirilmaz, L. Elci, M. Dogan, Speciation of Cr(III) and Cr (VI) in tannery wastewater and sediment samples on ambersorb 563 resin, Anal. Lett., 35/8 (2002) 1437-1452. DOI: 10.1081/AL-120006679
A. Gáspár, J. Posta, R. Tóth, On-line chromatographic separation and determination of chromium(III) and chromium(VI) with preconcentration of the chromium(III) using potassium hydrogen phthalate, in various samples by flame atomic absorption spectrometry, J. Anal. At. Spectrom. 11 (1996) 1067–1074. DOI: 10.1039/JA9961101067.   


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