Successful combination of benchtop nuclear magnetic resonance spectroscopy and chemometric tools: A review.

Low-field nuclear magnetic resonance (NMR) has three general modalities: spectroscopy, imaging, and relaxometry. In the last twelve years, the modality of spectroscopy, also known as benchtop NMR, compact NMR, or just low-field NMR, has undergone instrumental development due to new permanent magnetic materials and design. As a result, benchtop NMR has emerged as a powerful analytical tool for use in process analytical control (PAC). Nevertheless, the successful application of NMR devices as an analytical tool in several areas is intrinsically linked to its coupling with different chemometric methods. This review focuses on the evolution of benchtop NMR and chemometrics in chemical analysis, including applications in fuels, foods, pharmaceuticals, biochemicals, drugs, metabolomics, and polymers. The review also presents different low-resolution NMR methods for spectrum acquisition and chemometric techniques for calibration, classification, discrimination, data fusion, calibration transfer, multi-block and multi-way.

Data fusion of middle-resolution NMR spectroscopy and low-field relaxometry using the Common Dimensions Analysis (ComDim) to monitor diesel fuel adulteration.

Medium-resolution (MR-NMR) and time-domain NMR relaxometry (TD-NMR) using benchtop and low-field NMR instruments are powerful tools to tackle fuel adulteration issues. In this work, for the first time, we investigate the possibility of enhancing the low-field NMR capability on fuel analysis using data fusion of MR and TD-NMR. We used the ComDim (Common Dimensions Analysis) multi-block analysis to join the data, which allowed exploration, classification, and quantification of common adulterations of diesel fuel by vegetable oils, biodiesel, and diesel of different sources as well as the sulfur content. After data exploration using ComDim, classification (applying linear discriminant analysis, LDA), and regression (applying multiple linear regression, MLR), models were built using ComDim scores as input variables on the LDA and MLR analyses. This approach enabled 100% of accuracy in classifying diesel fuel source (refinery), sulfur content (S10 or S500), vegetable oil, and biodiesel source. Moreover, in the quantification step, all MLR models showed a root mean square error of prediction (RMSEP) and the residual prediction deviation (RPD) values comparable to the literature for determining diesel, vegetable oil, and biodiesel contents.

Compact low-field NMR spectroscopy and chemometrics applied to the analysis of edible oils.

Compact nuclear magnetic resonance (NMR) spectroscopy combined with chemometric tools opens new perspectives for NMR use. This work compares the potential of 43, 60 and 400 MHz NMR spectroscopy for quality control of edible oils. Partial least squares regression (PLSR) and support vector regression (SVR) models built on the three NMR devices had equivalent performances for fatty acids and iodine value, and the models built with the low field spectra were equivalent to the high field. Moreover, performances for calibration indicated that most of the models built with medium/or high-resolution fields presented reproducibility values lower than the minimum accepted by the American Oil Chemists' Society (AOCS). Compared to classical methods, this new approach allows the application of medium resolution devices as a sample screening tool in analytical laboratories since it allows the spectrum obtention in a few seconds, without the need for sample preparation or the use of deuterated solvents.

Calibration Transfer of Partial Least Squares Regression Models between Desktop Nuclear Magnetic Resonance Spectrometers.

Low-field proton nuclear magnetic resonance (LF-1H NMR) devices based on permanent magnets are a promising analytical tool to be extensively applied to the process analytical chemistry scenario. To enhance its analytical applicability in samples where the spectral resolution is compromised, multivariate regression methods are required. However, building a robust calibration model, such as partial least squares (PLS) regression, is a laborious task because (1) the number of measurements required during the calibration process is large and (2) the procedure must be repeated when the instrument is changed or after a certain period due to the long-term stability of the instrument. Thus, the present work describes the application of calibration transfer methodologies (direct standardization (DS), piece-wise direct standardization (PDS), and double-window piece-wise direct standardization (DWPDS)) on LF-1H NMR to exempt the necessity of a recalibration procedure when moving from the original spectrometer to a second one with the same, lower, or higher magnetic field. These calibration transfer methodologies were tested with PLS models built on a 60 MHz (for the proton Larmor frequency) spectrometer to predict the specific gravity (SG), distillation temperature (T50%), and final boiling point (FBP) of commercial gasoline. The results showed that the DWPDS method applying only 2 to 7 transference samples enables the transference of all PLS models built on the primary instrument (60 MHz) to other (43, 60, and 80 MHz) different instruments, reaching the same RMSEP values as the primary instrument: 1.2 kg/m3 for SG, 5.1 °C for FBP, and 1.1 °C for T50%.

Increasing the detection distance of remote NMR using wireless inductive coupling coil.

Unilateral nuclear magnetic resonance (UNMR) spectrometers have been applied in a variety of fields such as petrochemistry, materials science, and process control 1 . In UNMR measurements the sample is placed outside of the UNMR sensor and the signal intensity is reduced almost exponentially as the sample-to-sensor distances increases. To expand the detection limits of remote UNMR sensors, wireless inductive coupling was proposed and tested. This strategy was proved to reduce signal attenuation due to sample detachment from sensor, resulting in an increase in detection distance by one order of magnitude (i.e., from few millimeters to few centimeters). This novel approach broadens the potential applications of UNMR sensors and opens new opportunities in several areas, from chemical to biomedical applications.

Paralelos entre métodos fenotípicos, imunológicos e genotípicos para detecção rápida de Salmonella spp em matrizes alimentares sem contaminção experimental: avaliação em condições reais e simultâneas de uso / Parallels between phenotypic, genotypic and immunological methods for rapid detection of Salmonella spp in non-contaminated food matrices: evaluation in real conditions of use

Salmonella spp é um dos microrganismos patogênicos de relevância em alimentos. Sua detecção em alimentos por metodologia de cultura é trabalhosa e demorada, o que explica a grande variedade de sistemas automatizados e kits para detecção rápida desse patógeno existentes no mercado. Muitos desses métodos alternativos são validados por organizações internacionalmente reconhecidas, mas tais validações têm sido efetuadas em condições laboratoriais artificiais e com matrizes alimentares experimentalmente contaminadas, dificilmente refletindo a realidade de um laboratório de rotina de análises microbiológicas de alimentos. Nesse trabalho, avaliou-se o desempenho de sete métodos rápidos alternativos genotípicos e imunológicos, usados simultaneamente para detecção de Salmonella spp em 244 amostras de alimentos sem contaminação experimental, empregando o método de cultura ISO 6579:2002 como método de referência. Os métodos avaliados foram BAX Salmonella, VIDAS Salmonella, Transia Plate Salmonella Gold, VIP Salmonella, TECRA UNQUIQUE SALMONELLA, Singlepath Salmonella e 1-2 Test. O nível de detecção para cada método também foi-determinado. O método de referência detectou 50 amostras (20,5%) positivas para Salmonella spp. Nas condições em que o trabalho foi realizado, a porcentagem de concordância dos resultados positivos obtidos pelos métodos alternativos avaliados, em relação aos obtidos pelo método ISO 6579:2002 variou de 42,3% a 100%, dependendo do método avaliado e da matriz alimentar analisada...

Comparison of the BAX system PCR method to Brazil's official method for the detection of Salmonella in food, water, and environmental samples.

A two-stage study compared the BAX system PCR method with the reference culture method used by the Brazilian Ministry of Agriculture and Food Supply for the detection of Salmonella in food, water, and environmental samples. In stage 1, fish matrix samples (n = 258) were spiked at several levels with Salmonella and a combination of Salmonella and non-Salmonella competitive organisms. Replicates were analyzed by the BAX system PCR method and the reference method with comparable results (sensitivity > or = 97.5%, specificity > or = 83.3%) from both methods at the limit of detection. In stage 2, a total of 1,988 samples with 70 product types were analyzed with both methods. Five laboratories were involved in this study, and the samples used were from routine analyses. The BAX system PCR method was shown to be comparable to the reference method, with a limit of detection of 1.0 to 2.0 CFU/25 g of sample. Analysis of the results obtained in stage 2 and in the combination of stages 1 and 2 for the BAX system showed the following performance: sensitivity > or = 99.0%, specificity > or = 97.2%, false-negative rate < or = 1.1%, and false-positive rate < or = 2.8%. Therefore, the BAX system appears to be equivalent to the reference method, with > or = 97.3% agreement.