Determination of ammonia nitrogen in solid and liquid high-complex matrices using one-step gas-diffusion microextraction and fluorimetric detection.
This paper introduces a new method for a one-step determination of ammonia nitrogen (NH3) in high complex solid and liquid samples from the agricultural and livestock sectors. To this end, we developed a simultaneous extraction and fluorimetric labeling of NH3, using gas diffusion microextraction (GDME), followed by the fluorescence measurement under 96-well microplate format. The GDME ensured a selective diffusion of NH3through a commercial hydrophobic membrane, and confined the acceptor solution, which included the fluorimetric labeling reagent o-phthalaldehyde (OPA). The OPA-NH3labeling reaction was optimized resorting to a full factorial experimental design, which showed that the reducing agent (Na2SO3) concentration was critical to achieve the highest sensitivity. A similar optimization approach for GDME showed that time and temperature significantly influenced the sensitivity of the assay, and also that the modifications in these two factors could be used to adjust the sensitivity according to the concentrations present in the samples. In our final conditions, it was possible to quantify NH3in the range between 0.38 and 6.27mgL-1using a 10min extraction at 25°C in different samples (e.g., corn and grass silages, feces, urine). The developed method showed a high repeatability and reproducibility (intraday and interday relative standard deviations values of 4.5% and 9.5%, respectively) and an adequate limit of detection (0.22mgL-1). This new methodology also highlighted the simplicity and versatility of GDME for the determination of volatile components of high-complex matrices, which will certainly drive future developments in the analysis of environmental and biological samples.
REQUIMTE/LAQV - ICBAS, Departamento de Clínicas Veterinárias, Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Rua de Jorge Viterbo Ferreira no. 228, 4050-313 Porto, Portugal; REQUIMTE/LAQV - Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre no. 687, 4169-007 Porto, Portugal. Electronic address: ines.valente@fc.up.pt.
Inês M
IM
Valente
REQUIMTE/LAQV - ICBAS, Departamento de Clínicas Veterinárias, Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Rua de Jorge Viterbo Ferreira no. 228, 4050-313 Porto, Portugal.
Hugo M
HM
Oliveira
REQUIMTE/LAQV - Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre no. 687, 4169-007 Porto, Portugal.
Carlos D
CD
Vaz
REQUIMTE/LAQV - Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre no. 687, 4169-007 Porto, Portugal.
Rui M
RM
Ramos
REQUIMTE/LAQV - ICBAS, Departamento de Clínicas Veterinárias, Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Rua de Jorge Viterbo Ferreira no. 228, 4050-313 Porto, Portugal.
António J M
AJM
Fonseca
REQUIMTE/LAQV - ICBAS, Departamento de Clínicas Veterinárias, Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Rua de Jorge Viterbo Ferreira no. 228, 4050-313 Porto, Portugal.
Ana R J
ARJ
Cabrita
REQUIMTE/LAQV - Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre no. 687, 4169-007 Porto, Portugal.
José A
JA
Rodrigues
Ammonia nitrogen; Gas-diffusion microextraction; High-complex matrices; O-phthalaldehyde; Sample preparation