Avaliação da eficiência do método TO-15 para determinação de compostos orgânicos voláteis em condições típicas de ambiente urbano

Abstract

EVALUATION OF TO-15 METHOD EFICIENCY TO DETERMINE VOLATILE ORGANIC COMPOUNDS IN TYPICALURBAN CONDITIONS. The efficiency of U.S.EPA TO-15 Method was evaluated under typical conditions of an urban environment with natural and anthropic emission sources. The performance criteria which should be met for a system to qualify, were fulfilled: a detection limit of ≤0.2 ng for all target compounds, replicate precision for a calibration standard and ambient samples within 20%. The stability of the target compounds during storage of sampled air in canisters was also evaluated at atmospheric pressure and relative humidity of 50%. Results show that, in the sampling conditions, compounds are not stable for more than a week. For validation experiments, samples were collected at the entrance of Tijuca National Park, located at the city of Rio de Janeiro. Isoprene was selected as a marker of biogenic emissions, and aromatic compounds were selected as markers of anthropogenic emissions, primarily vehicular emissions. Then, samples were collected in Saens Peña Square, a central area in the Tijuca District, in the northern part of the city, approximately 10 km from the entrance of Tijuca National Park. Volatile organic compounds were determined and the results were compared with previous data obtained in the same local using other methods.Keywords: volatile organic compounds; isoprene; aromatic compounds; TO-15 method. INTRODUÇÃOSão definidos como compostos orgânicos voláteis (COVs) os compostos orgânicos cuja pressão de vapor a 20 °C é inferior à pressão atmosférica normal (1,013×10 5 Pa) e maior do que 130 Pa. 1 A legislação dos Estados Unidos 2 lista ainda 189 COVs considerados potencialmente perigosos para a saúde humana. Com o objetivo de atender às exigências da legislação, a Agência Ambiental dos Estados Unidos (U.S.EPA) desenvolveu o método TO-15, 3 que permite a determinação dos 97 principais compostos dessa lista. O método TO-15 estabelece os procedimentos gerais para a coleta de COVs usando canisters, botijões de aço inox eletropolidos internamente, e sua determinação utilizando a técnica de cromatografia gasosa acoplada à espectrometria de massas e termodessorção para injeção das amostras (CG-EM-DT). Estabelece também critérios de qualidade que devem ser atingidos na implementação do método: limite de detecção ≤ 0,5 ppbv, precisão das replicatas dentro de 25% e exatidão dentro do 30% para as concentrações esperadas em amostras ambientais (0,5 a 25 ppbv).Contudo, os resultados dependem de diversos fatores, tais como o processo de limpeza dos canisters, a umidade do ar coletado, o método de coleta, a estabilidade das amostras, as condições utilizadas na transferência das amostras e as condições cromatográficas, entre outras.A estabilidade das amostras é um fator crítico. Sob as condições normalmente encontradas em amostras ambientais é geralmente aceito que as amostras podem ser guardadas por trinta dias. [3][4][5] Entretanto, a estabilidade não é conhecida sobre condições variadas. Existe a possibilidade de perdas devida...

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