Validación del método generador de hidruros por espectrometría de absorción atómica para la determinación de arsénico en aguas naturales, de consumo y residuales

Abstract

This research validated the standardized Hydrides Generation, associated with Atomic Absorption Spectrometry (HG – AAS) to determine the total arsenic (As) in both, drinking water and sewage, with an interval of 0,010 – 0,178 mg/L, in conditions of repetitiveness and reproducibility at AqLab Environmental Evaluation and Analysis Laboratory, located in Puerto Francisco de Orellana. The natural and drinking water samples were acidified with HCI at 10% and pre-reduced with KI at 5%, while sewage samples were digested with H2SO4 2.5N and K2 S2 O8 at 5%. HCI at 10% (10 mL/min) was used as transporting solution, NaBH4 at 0,7% (5mL/min) diluted in NaOH at 0,05% as reducing agent and argon (100mL/min) as carrier gas at a temperature of 900°C of the quartz cell, C2H2 (6,5 L/min) as fuel, oxygen (4,4 L/min) as oxidant and a wavelength of 193.7 nm. The performance parameters determined through statistical evaluations with a level of confidence of 95% were: linearity (0,005 – 0,050 mg/L), detection limit (LD=0,003 mg/L) and quantification (LC=0,010 mg/L), the precision and accuracy (recovery from 95% to 105%) and uncertainty (U±7%). These parameters achieve the predefined validation objectives which guarantee that the testing method is under control and generates valid results with a confidence level accepted by AqLab, this will allow expanding its technical accreditation scope based on NTE INEN-ISO/IEC 17025:2018 norm by the Ecuadorian Accreditation Service (SAE) in order to meet the analytical customer demand. The interaction recommended between HCI and waste generation is 10mL/min and 11mL/min respectively. To avoid liquid increase in the gas/liquid separator, so that it is not transferred to the quartz cell and the interaction between HCI and NaBH4, it is necessary to keep a flow relation of 2:1 (10 mL/min – 5mL/min) to allow the appropriate generation of arsine (AsH3), which is a fundamental reaction of the method.