Minimization of volatile nitrogen oxides interference in the determinationof arsenic by hydride generation atomic absorption spectrometry

In this study emphasis was given to minimize the interference of volatile n itrogen oxides from digestion procedures with nitric acid on the determinat ion of arsenic by hydride generation atomic absorption spectrometry (HG AAS ). Sulfamic acid (SA) is proposed to minimize this interference by employin g three procedures for the digestion of hair in closed systems: conventiona l and microwave (MW) heating in polytetrafluorethylene (PTFE) vessels and b y MW heating in glass vials. Hair samples were digested with H2SO4 + HNO3 o r HNO3 + H2O2 mixtures. Concentrated hydrochloric acid was added for the di gestion for the procedure in glass vials. The accuracy of the procedures wi th PTFE vessels was verified by the spike recoveries of organic (p-aminoben zenearsonic acid and dimethyl arsinic acid, from 92 to 101%) and inorganic (sodium arsenate, from 98 to 102%) arsenic compounds. For the procedure in glass vials the recovery was from 86 to 97% for organic As and from 97 to 1 02% for inorganic As. The results obtained for a certified hair reference m aterial using the three digestion procedures were well within the 95% confi dence interval of the certificate when SA was added to the solutions. Howev er, when SA was not added, recoveries were low and non-reproducible signals and high background levels were observed. Urea, benzoic acid and hydroxyla mine hydrochloride were also studied (maximum As recovery of 90% using hydr oxylamine hydrochloride) but the best results were obtained with use of SA. (C) 2001 Elsevier Science B.V. All rights reserved.