Main content area

Determination of total arsenic and speciation analysis in Mexican maize tortillas by hydride generation – microwave plasma atomic emission spectrometry and high performance liquid chromatography – inductively coupled plasma – mass spectrometry

Guerrero Esperanza, Moises, Yanez Barrientos, Eunice, Wrobel, Kazimierz, Acevedo Aguilar, Francisco Javier, Corrales Escobosa, Alma Rosa, Wrobel, Katarzyna
Analytical methods 2017 v.9 no.13 pp. 2059-2068
anion exchange, arsenic, atomic absorption spectrometry, corn, cost effectiveness, high performance liquid chromatography, hydrides, markets, mass spectrometry, pH, silver chloride, sodium, tellurium, tortillas
The determination of total arsenic (tAs), inorganic As (iAs = As(iii) + As(v)) and As speciation in Mexican maize tortillas has been undertaken for the first time. Hydride generation – microwave plasma atomic emission spectrometry (HG-MP-AES) with tellurium (sodium tellurite Te(iv)) as the internal standard (IS) yielded tAs results in good agreement with those provided by inductively coupled plasma mass spectrometry (ICP-MS). In seven products from local markets, tAs was found in the range of 21.8–192 μg As kg⁻¹. Analysis of As(iii), As(v), MMAs(v), and DMAs(v) by an established anion exchange liquid chromatography – ICP-MS procedure showed that iAs corresponded to 72.3–98.0% of tAs. A non-chromatographic procedure was envisioned for iAs: diluted tortilla extract or calibration solution (pH 9.0) was loaded on a strong anion exchange cartridge modified with silver chloride, iAs fraction was collected and analyzed by HG-MP-AES with IS. For tAs by HG-MP-AES (with IS) the method quantification limit was 47.6 μg As kg⁻¹ whereas for iAs it got worse (95 μg As kg⁻¹) due to the low recovery of this As form in SPE (<30%). In an attempt to eliminate matrix interference, the lower sample volume was loaded on the cartridge and ICP-MS was used for quantification, yielding an improved percentage recovery of 73.4%. On the other part, the iAs recovery was >93% while analyzing natural water with off-line quantification by any of the two atomic spectrometry techniques, indicating that the chemical matrix of tortillas was responsible for poor SPE performance. It is concluded that HG-MP-AES with IS is a cost-effective alternative for the determination of tAs that offers improved precision under a non-rigorous protocol; however, efficient separation/preconcentration of iAs by SPE is still a challenge.