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

Abstract

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.