Pablo Nogueira Teles Moreira

Implementation of an automatic standard addition method in a flow–batch system: application to copper determination in an alcoholic beverage by atomic absorption spectrometry

A novel strategy for implementing the automatic standard addition method (SAM) is described. By using a flow–batch system that presents the intrinsic favourable characteristics of the flow and batch techniques, the proposed strategy performs fast standard additions with sufficient flexibility and versatility and employs only one standard solution per analyte. To calculate the analyte concentration, a mathematical model based on a classical SAM and flow variables of the system was developed. The proposed flow–batch SAM was applied to copper determination by flame atomic absorption spectrometry (AAS) in sugar cane-made alcoholic beverages, known as “Cachaca”, available in Brazil. A SAM has been recommended for these analyses because “Cachacas” presents a significantly different composition causing matrix effects and copper determination by calibration using matrix-matching standards can yield inaccurate results. The results show good agreement between the obtained values with the proposed flow–batch SAM and a manual SAM. The mean relative errors and overall standard deviations were always <1.0% (n = 6) and 0.2 mg l −1 , respectively, for 1.0–7.0 mg l −1 Cu. By using five standard addition levels, the sample throughput was 70 h −1 and the consumption of sample and standard solution were 1.5 and 0.5 ml per

An automatic flow-batch standard-addition method for sodium determination in alcohol fuel by flame photometry

The Brazilian Regulatory Agency for fuel production and commercialization requires that the sodium concentration in alcohol fuel should be determined by flame photometry and that the analytical curves should be obtained with matrix-matched standards. Notwithstanding, this methodology can produce inexact results because alcohol fuel presents a significant variability in matrix composition and, consequently, in the matrix effect. This problem can be circumvented by using the standard addition method (SAM). However, this method is slow and laborious when it carried out by manual procedures. To overcome these drawbacks, an automatic flow-batch SAM for sodium determination in alcohol fuel by flame photometry is described. This system requires only one standard solution, handles about 80 - 140 samples per hour and consumes a total volume of sample and of standard solution smaller than 1.5 mL for each analysis. The results present a standard deviation usually less than 0.1 mg L-1 (n = 4).

Flow Injection Determination of Metronidazole through Spectrophotometric Measurement of the Nitrite Ion Produced upon Alkaline Hydrolysis

A new method for metronidazole determination, based on spectrometric monitoring of a diazonium salt produced in-line by alkaline hydrolysis released nitrite ions, was developed and successfully applied to pharmaceutical tablets (r = 0.9993, 2.0-20.0 mg L-1, DL = 0.7 mg L-1) with no interference from common ingredients accompanying the drug.

An automatic flow system for NIR screening analysis of liquefied petroleum gas with respect to propane content

This paper proposes a NIR spectrometric method for screening analysis of liquefied petroleum gas (LPG) samples. The proposed method is aimed at discriminating samples with low and high propane content, which can be useful for the adjustment of burn settings in industrial applications. A gas flow system was developed to introduce the LPG sample into a NIR flow cell at constant pressure. In addition, a gas chromatographer was employed to determine the propane content of the sample for reference purposes. The results of a principal component analysis, as well as a classification study using SIMCA (soft independent modeling of class analogies), revealed that the samples can be successfully discriminated with respect to propane content by using the NIR spectrum in the range 8100-8800 cm(-1). In addition, by using SPA-LDA (linear discriminant analysis with variables selected by the successive projections algorithm), it was found that perfect discrimination can also be achieved by using only two wavenumbers (8215 and 8324 cm(-1)). This finding may be of value for the design of a dedicated, low-cost instrument for routine analyses.

Um fotômetro multi-led microcontrolado, portátil e de baixo custo

A microcontrolled, portable and inexpensive photometer is described. It uses six light-emitting diodes (LEDs) as radiation sources and a phototransistor as detector, as well as a microcontroller (PIC - Programmable Controller of Interruption). This device provided total autonomy to the proposed photometer, which was successfully applied to determination of Fe2+ in ferrous syrups and of seven clinical biochemical parameters. As the components are cheap (~U

Use of an Automatic System in the Preparation of Gas Mixtures for Multivariate Calibration: A Case Study Involving NIR Analysis of Natural Gas

30.00) and easy to find, the proposed photometer is an economical alternative for routine chemical analyses in small laboratories, for research and teaching. Being portable and microcontrolled, it allows doing field chemical analyses.

The successive projections algorithm for spectral variable selection in classification problems

This paper investigates the use of an automatic system for preparation of gas mixtures in a multivariate calibration problem involving near-infrared (NIR) spectrometric analysis of natural gas. The automatic system is used to prepare calibration mixtures according to a Brereton experimental design, in order to exploit a suitable range of gas concentrations and thus avoid extrapolations in the predictions. These mixtures were employed to build partial-least-squares models for NIR determination of methane, ethane and propane, which are the major components of natural gas. Prediction performance was evaluated by using a separate set of prepared mixtures and natural gas samples with composition analyzed by gas chromatography, as well as a group of certified mixtures. The resulting root-mean-square errors of prediction (RMSEP) values for methane, ethane and propane (3.0, 0.9 and 1.2% mol mol-1, respectively) were approximately 10 times smaller than the corresponding calibration ranges, with correlations of 0.91, 0.96 and 0.86 between the predicted and reference values.