Estudo de reação colorimétrica para desenvolvimento de método para determinação de formaldeído na atmosfera
Carregando...
Data
2023-06-27
Autores
Catai, Marcus Augusto dos Santos
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
O formaldeído (CH2O) é um dos compostos orgânicos voláteis (COVs) mais abundantes no ar atmosférico de cidades poluídas. É também muito comum ser encontrado no ar de ambientes fechados, mobiliados com móveis feitos com madeira processada. A necessidade de identificar e quantificar o formaldeído é resultado de suas características genotóxicas que pode piorar a saúde de indivíduos que já têm uma saúde debilitada e de pessoas saudáveis, afetando sua qualidade de vida. Atualmente os métodos utilizados para se quantificar CH2O no ar tem um custo elevado e necessitam de pessoal capacitado. O objetivo desse trabalho foi aplicar um método analítico para determinação de formaldeído presente no ar atmosférico, construir um equipamento portátil e de baixo custo e verificar a influência de ozônio, COVs, umidade e temperatura na formação de formaldeído. O método pode ajudar em estudos de monitoramento ambiental e identificação de possíveis fontes. Inicialmente foi montado um sistema dinâmico para produção de solução gasosa padrão de formaldeído. Um tubo de permeação de formaldeído foi confeccionado como fonte padrão de formaldeído, no qual foram injetados 5 mL de solução padrão de formaldeído 37% em uma vidraria com formato de ampola (Ø 9,0 mm e altura 4,0 cm) com uma saída estreita (Ø 7,0 mm e com comprimento e comprimento 4,0 cm) conectada a um tubo de Teflon (Ø interno de 7 mm, espessura de 1 mm e comprimento de 5,2 cm) selado com LED (Ø 5,0 mm) recoberto por um filme de teflon. A taxa de emissão do tubo foi determinada como 27 ± 2 ngCH2O min-1 a 26 ± 0,1°C e devido ao intervalo de volume das válvulas de fluxo, foram preparadas concentrações de 31, 37, 44, 55, 73, 110 ppbv de CH2O, necessárias para estabelecer o volume, a vazão e o tempo, variáveis que afetam a amostragem do gás. O reagente escolhido foi o 3-Metil-2-Benzotiazolinona Hidrazona (MBTH) devido a sua reação com CH2O formar um cátion de absorção máxima no λ= 628 nm. O volume de 500µL MBTH 0,05% foi utilizado para borbulhar as concentrações de CH2O, com vazão de 50 mL min -1 , por 30 minutos e posteriormente 12 minutos foram aguardados para a finalização da primeira etapa da cinética da reação e na sequência foram adicionados 120 µL de uma solução oxidante de Cloreto de Ferro (3,8x10-3 mol L-1 ) com Ácido Sulfâmico (0,1 mol L -1 ). Após 5 minutos para a completa formação do cátion, foi realizada a leitura das absorbâncias das soluções tanto no fotômetro construído quanto no espectrofotômetro com a finalidade de comparação dos resultados. Foram gastos R$250,00 na construção do fotômetro que apresentou um Limite de Detecção (LOD) de 7 ppbv e Limite de Quantificação (LOQ) de 22 ppbv enquanto espectrofotômetro apresentou um LOD de 0,6 ppbv e um LOQ de 2 ppbv. A partir do método foi possível verificar a influência do ozônio e de COVs como fonte de formaldeído e realizar medidas de CH2O em ambientes fechados (24 a 81 ppbv) e abertos (12 ppbv).
Formaldehyde (CH2O) is one of the most abundant volatile organic compounds (VOCs) in the atmospheric air of polluted cities. It is also commonly found in the indoor air of furnished spaces with processed wood furniture. The need to identify and quantify formaldehyde is a result of its genotoxic characteristics, which can worsen the health of individuals with pre-existing health conditions and healthy individuals, affecting their quality of life. Currently, the methods used to quantify CH2O in the air are costly or require trained personnel. The objective of this study was to apply an analytical method for the determination of formaldehyde in the atmospheric air, build a portable and low-cost equipment, and investigate the influence of ozone, VOCs, humidity, and temperature on the formation of formaldehyde. The method can assist in environmental monitoring studies and identification of possible sources. Initially, a dynamic system was set up for the production of a standard gas solution of formaldehyde. A formaldehyde permeation tube was fabricated as a standard formaldehyde source, in which 5 mL of a 37% standard formaldehyde solution was injected into a glassware with an ampoule shape (Ø 9.0 mm and height 4.0 cm) with a narrow outlet (Ø 7.0 mm and length 4.0 cm) connected to a Teflon tube (inner diameter 7 mm, thickness 1 mm, and length 5.2 cm) sealed with an LED (Ø 5.0 mm) covered with a Teflon film. The emission rate of the tube was determined to be 27 ± 2 ngCH2O min-1 at 26 ± 0.1°C, and concentrations of 31, 37, 44, 55, 73, 110 ppbv of CH2O were prepared due to the flow valve volume range, which were necessary to establish the volume, flow rate, and time, variables that affect gas sampling. The chosen reagent was 3-Methyl-2-Benzothiazolinone Hydrazone (MBTH) due to its reaction with CH2O to form a cation with maximum absorption at λ= 628 nm. A volume of 500μL of 0.05% MBTH was used to bubble the CH2O concentrations, with a flow rate of 50 mL min-1 for 30 minutes, and then a 12-minute waiting period was observed to complete the first stage of the reaction kinetics. Subsequently, 120 μL of an oxidizing solution of Iron Chloride (3.8x10-3 mol L-1) with Sulfamic Acid (0.1 mol L-1) was added. After 5 minutes for the complete formation of the cation, the absorbance’s solutions were measured both in the constructed photometer and in the spectrophotometer for comparison of the results. The construction of the photometer cost R$250.00 and it presented a Limit of Detection (LOD) of 7 ppbv and a Limit of Quantification (LOQ) of 22 ppbv, while the spectrophotometer had an LOD of 0,6 ppbv and an LOQ of 2 ppbv. Using the method, it was possible to observe the influence of ozone and VOCs as sources of formaldehyde and measure CH2O levels indoor (24 to 81 ppbv) and outdoor (12 ppbv).
Formaldehyde (CH2O) is one of the most abundant volatile organic compounds (VOCs) in the atmospheric air of polluted cities. It is also commonly found in the indoor air of furnished spaces with processed wood furniture. The need to identify and quantify formaldehyde is a result of its genotoxic characteristics, which can worsen the health of individuals with pre-existing health conditions and healthy individuals, affecting their quality of life. Currently, the methods used to quantify CH2O in the air are costly or require trained personnel. The objective of this study was to apply an analytical method for the determination of formaldehyde in the atmospheric air, build a portable and low-cost equipment, and investigate the influence of ozone, VOCs, humidity, and temperature on the formation of formaldehyde. The method can assist in environmental monitoring studies and identification of possible sources. Initially, a dynamic system was set up for the production of a standard gas solution of formaldehyde. A formaldehyde permeation tube was fabricated as a standard formaldehyde source, in which 5 mL of a 37% standard formaldehyde solution was injected into a glassware with an ampoule shape (Ø 9.0 mm and height 4.0 cm) with a narrow outlet (Ø 7.0 mm and length 4.0 cm) connected to a Teflon tube (inner diameter 7 mm, thickness 1 mm, and length 5.2 cm) sealed with an LED (Ø 5.0 mm) covered with a Teflon film. The emission rate of the tube was determined to be 27 ± 2 ngCH2O min-1 at 26 ± 0.1°C, and concentrations of 31, 37, 44, 55, 73, 110 ppbv of CH2O were prepared due to the flow valve volume range, which were necessary to establish the volume, flow rate, and time, variables that affect gas sampling. The chosen reagent was 3-Methyl-2-Benzothiazolinone Hydrazone (MBTH) due to its reaction with CH2O to form a cation with maximum absorption at λ= 628 nm. A volume of 500μL of 0.05% MBTH was used to bubble the CH2O concentrations, with a flow rate of 50 mL min-1 for 30 minutes, and then a 12-minute waiting period was observed to complete the first stage of the reaction kinetics. Subsequently, 120 μL of an oxidizing solution of Iron Chloride (3.8x10-3 mol L-1) with Sulfamic Acid (0.1 mol L-1) was added. After 5 minutes for the complete formation of the cation, the absorbance’s solutions were measured both in the constructed photometer and in the spectrophotometer for comparison of the results. The construction of the photometer cost R$250.00 and it presented a Limit of Detection (LOD) of 7 ppbv and a Limit of Quantification (LOQ) of 22 ppbv, while the spectrophotometer had an LOD of 0,6 ppbv and an LOQ of 2 ppbv. Using the method, it was possible to observe the influence of ozone and VOCs as sources of formaldehyde and measure CH2O levels indoor (24 to 81 ppbv) and outdoor (12 ppbv).
Descrição
Palavras-chave
Formaldeído, Poluição do ar de interiores, Espectrofotômetro, Ozônio atmosférico, Análise colorimétrica