Determination of Inorganic Arsenic in a Wide Range of Food Matrices using Hydride Generation - Atomic Absorption Spectrometry.

The overall goal of this analytical methodology is to determine inorganic arsenic in a wide range of food samples by means of a selective extraction and detection by hydride generation atomic absorption spectroscopy.This is a horizontal method that allows the determination of inorganic arsenic.The most toxic arsenic species found in fruit products.The main advantage of this technique is that the instrumentation needed is not that expensive and sophisticated as for HPLC-ICP-MS, and the selectivity is better than that of direct hydrated generation atomic absorption spectroscopy.Demonstrating this procedure will be Dinoraz Velez.One our the co-authors of this paper and a researcher from our laboratory.To begin, accurately weigh 0.5 to 1 gram of lyophilized sample in a 50ml polypropylene centrifuge tube with screw cap.Add 4.1ml of deionized water.Then, agitate the sample with a mechanical shaker for about five minutes until the sample is completely wet.Add 18.4ml of concentrated hydrochloric acid.Agitate with a mechanical shaker for 15 minutes before letting the sample rest for 12 to 15 hours.To perform the extraction, first add 2ml of Hydrogen Bromide and 1ml of Hydrogen Sulfate solution to the hydrolyzed sample.Shake the sample for 30 seconds with a mechanical shaker or manually.Then, add 10ml of Chloroform.After shaking the sample for five minutes with a mechanical shaker, centrifuge for five minutes at 800 times g.Following centrifugation, pipette the Chloroform phase into another 50ml polypropylene centrifuge tube.Add an additional 10ml of Chloroform to the remaining acid phase and repeat the extraction.Following extraction, approximately 20ml of Chloroform should have been collected.Take care to avoid cross-contamination from the acid phase.Centrifuge the pooled Chloroform phases for five minutes at 800 times g.Remove all acid phase residues remaining on the Chloroform with a 1ml pipette.Next, filter the Chloroform through a hydrophobic PTFE membrane to remove the remaining solid or acid phase residues present in the Chloroform phase.Collect the Chloroform phase in a 50ml polypropylene centrifuge tube.This step is crucial.Any acid phase remaining in the Chloroform phase will lead to overestimated inorganic arsenic results because all other arsenic species in the sample are present in this acid phase.To perform back extraction, add 10ml of one molar hydrochloric acid to back extract inorganic arsenic from the Chloroform phase, collected after the filtration step.Then, shake the sample for five minutes with a mechanical shaker.Centrifuge the sample for five minutes at 800 times g.Following centrifugation, pipette the acid phase into a 250ml glass beaker for mineralization.Repeat the back extraction and combine the collected HCl phases.Suspend 20 grams of Magnesium nitrate hexahydrate and two grams of Magnesium oxide in 100ml of deionized water.Then, add 2.5ml of this suspension to the glass beaker, shake the suspension while adding it to avoid precipitation.Next, add 10ml of concentrated nitric acid and evaporate to dryness in a sand bath, avoiding any projections.Cover the beaker with a watch glass or something similar.Then, place the beaker in a muffle furnace at an initial temperature, not exceeding 150