Aplicação de espectroscopia no infravermelho próximo e análise multivariada para identificação e quantificação de hidrocarbonetos totais do petróleo em solo
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Data
2018-08-31
Autores
Nespeca, Maurílio Gustavo
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Universidade Estadual Paulista (Unesp)
Resumo
Segundo dados, de 2017, da Companhia Ambiental do Estado de São Paulo (CETESB), os postos de combustíveis são responsáveis pela contaminação ambiental de 72% das 5942 áreas contaminadas cadastradas no estado de São Paulo. A contaminação de solos e águas subterrâneas por combustíveis fósseis causam imensos danos ambientais devido à alta toxicidade dos constituintes destes combustíveis, além de apresentarem propriedades carcinogênicas e elevada permanência no solo. O monitoramento ambiental em áreas de risco potencial de contaminação, como postos de combustíveis, é realizado através da análise de hidrocarbonetos totais do petróleo (TPH), entre outros hidrocarbonetos individuais. Estas análises são realizadas através de métodos cromatográficos em fase gasosa que requerem etapas de extração com solventes halogenados, purificação e, muitas vezes, pré-concentração. O elevado custo e o tempo demandado para a quantificação de TPH em solo tornam-se barreiras para o crescimento do monitoramento e acompanhamento de processos de remediação das áreas contaminadas. Desta forma, este trabalho objetivou o desenvolvimento de métodos analíticos mais rápidos e de menor custo para a identificação e quantificação de TPH em solo através da espectroscopia na região do infravermelho próximo (NIR). Três métodos NIR foram desenvolvidos: (i) sem preparo de amostra; (ii) após extração por hexano; e (iii) após extração por etanol. Os modelos de classificação foram desenvolvidos pelo método de análise discriminante por mínimos quadrados parciais (PLS-DA) e os modelos de calibração por mínimos quadrados parciais (PLS). No desenvolvimento dos modelos, nove diferentes pré-processamentos e seleção de variáveis pelo algoritmo genético (GA) foram avaliados. Os modelos foram desenvolvidos usando-se amostras de solo fortificado com os contaminantes (gasolina, diesel e óleo lubrificantes) e validados com amostras de solo contaminado, adquiridas no monitoramento ambiental de postos de combustíveis. O modelo PLS-DA proporcionou 100% de classificações corretas das amostras contaminadas sem a necessidade de preparo de amostra, enquanto a predição da concentração dos analitos tornou-se possível através dos modelos PLS após a etapa de extração com etanol. Como objetivos secundários deste trabalho, foram desenvolvidos métodos de quantificação das diferentes frações de TPH e dos compostos benzeno, tolueno, etilbenzeno e xilenos (BTEX) por cromatografia em fase gasosa ultrarrápida com detector de ionização por chama (UFGC-FID). Além do desenvolvimento dos métodos UFGC-FID, otimizou-se o processo de extração dos analitos por sonicação através de planejamentos experimentais, avaliando-se diferentes solventes, tempo de sonicação, agitação por vórtex e volume de solvente. Os métodos UFGC-FID proporcionaram análises de 3 a 17 vezes mais rápidas que o método cromatográfico de acordo com a norma EPA 8015. Ao final deste trabalho, os métodos desenvolvidos e o método EPA 8015 foram comparados segundo aspectos analíticos, ambientais e financeiros. De forma geral, os três métodos apresentaram mesma exatidão; o método cromatográfico (EPA 8015) foi o método mais preciso; o método UFGC-FID foi o de menor investimento inicial e de menor tempo para retorno financeiro; e, finalmente, o método NIR após extração com etanol foi o mais sensível, rápido, favorável à química verde e de menor custo por análise.
According to the Environmental Company of the State of São Paulo (CETESB), the gas stations are responsible for the environmental contamination of 72% of the 5942 contaminated areas registered in the state of São Paulo. Contamination of soils and groundwater by fossil fuels causes immense environmental damages due to their high toxicity, carcinogenic properties and high permanence in the soil. Environmental monitoring in areas of potential contamination risk, such as gas stations, is carried out through the analysis of total petroleum hydrocarbons (TPH), among other individual compounds. These analyzes are performed by gas chromatographic methods which require some sample preparation steps, such as extraction with halogenated solvents, purification, and often preconcentration. The high cost and time demanded for the quantification of TPH in the soil become barriers for the growth of the monitoring program and remediation processes of the contaminated areas. Therefore, this work aimed at the development of faster and lower cost analytical methods for the identification and quantification of TPH in soil through near-infrared spectroscopy (NIR). Three NIR methods were developed: (i) without sample preparation; (ii) after hexane extraction; and (iii) after extraction with ethanol. The classification models were developed by partial least squares discriminant analysis (PLS-DA) method and the calibration models by partial least squares (PLS) method. In the development of the models, we evaluated nine different preprocessing and selection of variables by the genetic algorithm (GA). The models were developed using soil samples fortified with contaminants (gasoline, diesel and lubricant oil) and validated with samples of contaminated soil acquired in the environmental monitoring of gas stations. The PLS-DA model provided 100% correct classifications without sample preparation, while the prediction of the concentration of the analytes was possible by PLS models after the ethanol extraction. As secondary objectives of this work, we developed quantification methods for the different fractions of TPH and benzene, toluene, ethylbenzene, and xylenes (BTEX) compounds by ultrafast gas chromatography with flame ionization detector (UFGC-FID). In addition to the UFGC-FID methods, the TPH extraction by sonication was optimized through experimental design, evaluating different solvents, sonication time, agitation and solvent volume. The UFGC-FID methods provided analyzes 3 to 17 times faster than the chromatographic method according to EPA 8015. At the end of this work, the developed methods and the EPA 8015 method were compared according to analytical, environmental and financial aspects. In general, the three methods presented the same accuracy; the EPA 8015 method was the most precise; the UFGC-FID method presented lower initial investment and less time for financial return; and the NIR method after ethanol extraction was the most sensitive, fast, favorable to green chemistry and presented the lowest cost per analysis.
According to the Environmental Company of the State of São Paulo (CETESB), the gas stations are responsible for the environmental contamination of 72% of the 5942 contaminated areas registered in the state of São Paulo. Contamination of soils and groundwater by fossil fuels causes immense environmental damages due to their high toxicity, carcinogenic properties and high permanence in the soil. Environmental monitoring in areas of potential contamination risk, such as gas stations, is carried out through the analysis of total petroleum hydrocarbons (TPH), among other individual compounds. These analyzes are performed by gas chromatographic methods which require some sample preparation steps, such as extraction with halogenated solvents, purification, and often preconcentration. The high cost and time demanded for the quantification of TPH in the soil become barriers for the growth of the monitoring program and remediation processes of the contaminated areas. Therefore, this work aimed at the development of faster and lower cost analytical methods for the identification and quantification of TPH in soil through near-infrared spectroscopy (NIR). Three NIR methods were developed: (i) without sample preparation; (ii) after hexane extraction; and (iii) after extraction with ethanol. The classification models were developed by partial least squares discriminant analysis (PLS-DA) method and the calibration models by partial least squares (PLS) method. In the development of the models, we evaluated nine different preprocessing and selection of variables by the genetic algorithm (GA). The models were developed using soil samples fortified with contaminants (gasoline, diesel and lubricant oil) and validated with samples of contaminated soil acquired in the environmental monitoring of gas stations. The PLS-DA model provided 100% correct classifications without sample preparation, while the prediction of the concentration of the analytes was possible by PLS models after the ethanol extraction. As secondary objectives of this work, we developed quantification methods for the different fractions of TPH and benzene, toluene, ethylbenzene, and xylenes (BTEX) compounds by ultrafast gas chromatography with flame ionization detector (UFGC-FID). In addition to the UFGC-FID methods, the TPH extraction by sonication was optimized through experimental design, evaluating different solvents, sonication time, agitation and solvent volume. The UFGC-FID methods provided analyzes 3 to 17 times faster than the chromatographic method according to EPA 8015. At the end of this work, the developed methods and the EPA 8015 method were compared according to analytical, environmental and financial aspects. In general, the three methods presented the same accuracy; the EPA 8015 method was the most precise; the UFGC-FID method presented lower initial investment and less time for financial return; and the NIR method after ethanol extraction was the most sensitive, fast, favorable to green chemistry and presented the lowest cost per analysis.
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Palavras-chave
Hidrocarbonetos totais do petróleo, Contaminação de solo, Espectroscopia no infravermelho próximo, Modelos de classificação, Modelos de calibração, Cromatografia em fase gasosa ultrarrápida, Total petroleum hydrocarbons, Soil contamination, Near-infrared spectroscopy, Classification models, Calibration models, Ultrafast gas chromatography