Quantitative Determination Of Water Content Research Articles

Cheese quality assessment by use of near-infrared spectroscopy

Dairy products are worldwide spread and have great commercial importance. Rapid and reliable analysis of cheese would be highly desirable both for the manufacturers and consumers. The results of experiments, related to the application of near-infrared spectroscopy for cheese quality estimation will be presented. Several kinds of Bulgarian white brine cheese - natural from cow milk, imitation products with vegetable oil, and cheese with different water content were investigated. Fatty acids composition of samples was determined by using gas chromatography and moisture content by the oven-dry method. Spectra of all tested samples were obtained with a scanning NIRQuest 512 (Ocean Optics, Inc.) instrument in the range of 900-1700 nm using a reflection fiber-optics probe. PLS models were developed for quantitative determination and SIMCA for classification. The misclassification rate of the SIMCA model for discrimination of natural cheese and imitation products with vegetable oil was 2.9%. Quantitative determination of water content based on NIR spectra showed high accuracy, Models for classification of cheese samples into 3 groups according to water content achieved 5.64% misclassification rate for the independent test set. Results showed the potential of near-infrared spectroscopy as a non-destructive and rapid screening tool for assessing cheese quality and detecting adulteration.

Solvatochromic fluorescent styryl pyrene probes for the quantitative determination of water content in organic solvents

A series of D-π-A fluorescent styryl pyrene probes were synthesized through the Wittig reaction. The introduction of an electron-withdrawing substituent on the phenyl ring creates a push-pull system that shows solvent-dependent intramolecular charge transfer (ICT) and solvatochromic properties. Among these, the styryl pyrene probes with nitro (Py-NO2) and aldehyde (Py-CHO) substituents exhibited remarkable sensitivity to environment polarity. They show remarkable fluorescence changes from green to red, and blue to orange in nonpolar to polar organic solvents, respectively. The results were explained by the Lippert-Mataga and ET(30) models, which were supported by theoretical calculations by the density functional theory (DFT). Importantly, the fluorescence emission of Py-NO2 in organic solvents is sensitive to the presence of water in the range of 0–34.2% (v/v) in THF, 0–9.1% (v/v) in DMF, and 0–39.7% (v/v) in CH3CN. The limits of detection of water were established as low as 0.007%, 0.033%, and 0.036% (v/v) in THF, DMF, and CH3CN, respectively. Py-CHO showed somewhat higher limits of detection than Py-NO2 for the same solvents but exhibited a broad linear response to water content in EtOH between 3.3 and 63.6% (v/v) water content with the limit of detection at 2.350% (v/v). Thus, it is possibly useful as a sensor for the wide range detection of alcohol content in beverages. These push-pull styryl pyrene probes not only served as a new supersensitive fluorescent sensor for the quantitative detection of low to medium-level water content in organic solvents but may also be useful in a broad range of applications.

Comparative analysis of the methods for quantitative determination of water content in skin from diffuse reflectance spectroscopy data

The predictive properties of methods aimed for estimating the water content in skin from the spectral diffuse reflection characteristics near the water absorption line in the near-IR spectral range are analysed. Numerical simulation data, experimental data on diffuse reflection from human skin phantoms, and data from the reference data set of human skin reflectance spectra are used to consider the possibility of gaining additional information about the water distribution in skin. The influence of variations in the scattering coefficient and oxyhaemoglobin concentration on the water content estimates is investigated.

Quantification of Water, Protein and Soluble Sugar in Mulberry Leaves Using a Handheld Near-Infrared Spectrometer and Multivariate Analysis.

Mulberry (Morus alba L.) leaves are not only used as the main feed for silkworms (Bombyx mori) but also as an added feed for livestock and poultry. In order to rapidly select high-quality mulberry leaves, a hand-held near-infrared (NIR) spectrometer combined with partial least squares (PLS) regression and wavelength optimization methods were used to establish a predictive model for the quantitative determination of water content in fresh mulberry leaves, as well as crude protein and soluble sugar in dried mulberry leaves. For the water content in fresh mulberry leaves, the R-square of the calibration set (), R-square of the cross-validation set () and R-square of the prediction set () are 0.93, 0.90 and 0.91, respectively, the corresponding root mean square error of calibration set (RMSEC), root mean square error of cross-validation set (RMSECV) and root mean square error of prediction set (RMSEP) are 0.96%, 1.13%, and 1.18%, respectively. The , and of the crude protein prediction model are 0.91, 0.83 and 0.92, respectively, and the corresponding RMSEC, RMSECV and RMSEP are 0.71%, 0.97% and 0.61%, respectively. The soluble sugar prediction model has , , and of 0.64, 0.51, and 0.71, respectively, and the corresponding RMSEC, RMSECV, and RMSEP are 2.33%, 2.73%, and 2.36%, respectively. Therefore, the use of handheld NIR spectrometers combined with wavelength optimization can fastly detect the water content in fresh mulberry leaves and crude protein in dried mulberry leaves. However, it is a slightly lower predictive performance for soluble sugar in mulberry leaves.

The coumarin conjugate: synthesis, photophysical properties and the ratiometric fluorescence response to water content of organic solvent

A new fluorescent probe based on coumarin conjugate has been synthesized which shows high quantum yield because of strong ICT effect. The absorption and fluorescence spectra of probe were measured in a variety of solvents and the Stokes shifts were found to be in linear relationship with the orientation polarizability of the solvents. The fluorescence intensity of probe decreased with a rise in water content which could be an effective fluorescence water sensor in organic solvents. Moreover, the probe presents a highly linear ratiometric fluorescence response to water content under the excitation of ultraviolet light. The detection results by the ratiometric fluorescence probe are in good agreement with that by the well-established standard Karl Fischer method. This ratiometric fluorescent probe provides another accessible tool for the quantitative determination of water content and may replace the Karl Fischer method for specific applications.

Fiber-optic sensor based on evanescent wave absorbance around 2.7 μm for determining water content in polar organic solvents

The feasibility of sapphire fiber-optic sensors based on evanescent wave absorption spectroscopy in the infrared range for quantitative determination of water content in polar organic solvents has been investigated. Evanescent wave absorption spectra of sapphire fiber-optic sensors in glycerol, ethanol, and glycol with different water concentrations obtained and analyzed, respectively. Evanescent absorbance of the sensors in those organic solvents has been utilized to implement for in situ monitoring water concentration in organic solvents. The evanescent absorbance of sensors in glycerol and glycol has been found to vary linearly with water content in the range 0–30 % and in ethanol in the range 0–10 %, respectively. The fiber-optic sensors based on evanescent absorbance for monitoring water concentrations in those organic solvents are acceptably accurate, cost-effective, and reliable. Some methods to improve the accuracy of predicated water content in those organic solvents are also suggested. Overall, the results demonstrate that the sapphire fiber-optic sensor based on evanescent absorption spectroscopy is a promising candidate for prediction of water content in polar organic solvents in on-line and remote situation.

Determination of water content in silica nanopowder using wavelength-dispersive X-ray fluorescence spectrometer

A wavelength-dispersive X-ray fluorescence (WDXRF) technique that uses the scattered radiation of the X-ray tube lines and the fluorescence radiation of an element present in a powder sample is proposed as a non-destructive method for the determination of the water content in silica powder. Although direct X-ray fluorescence analysis of water using WDXRF is not adequate for the quantitative determination of water in powder, due to the very low fluorescence yield for hydrogen and oxygen, the fluorescence signal of silicon (Si) in silica powder is attenuated by water, and is shown to decrease in proportion to the water content in silica powder. In addition, it is demonstrated that the Compton- and Rayleigh-scattering of the X-ray tube lines is proportional to the water content. The coefficients of determination, R2, of the linear regression equations obtained from the calibration curves for all individual scattered radiations and for the fluorescence radiation of Si were >0.90. The sum of the peak intensities of the four scattering signals, i.e. the Rayleigh-scattered Rh K–L2,3 and Rh K–M2,3 lines, and Compton-scattered Rh K–L2,3 and Rh K–M2,3 lines, also showed fairly good linearity and sensitivity over a very wide range of water content from 0wt.% to 61.5wt.%. However, porosity had a significant effect on the X-ray signal at low water content, in the range from 0wt.% to 7.5wt.%, where the sensitivity for the silica nanopowder with well-defined mesopores (~3nm in diameter) decreased to 0.40kcps/wt.%, from 0.99kcps/wt.% for the non-porous silica nanopowder. The use of the Si fluorescence signal along with the scattered radiation of the X-ray tube lines expands the applicability of conventional XRF spectrometers to the quantitative determination of water content in silica powder.

Thermal dehydration of some food products and kinetic parameters of this process

The derivatographic method was used for the quantitative determination of water content in selected flour and fat products. Weight losses and thermal effects taking place in the examined products under the influence of heat were read from the obtained derivatograms. Percentage water contents were calculated from TG curves within the range from 5.6% (rice cereal) to 16.0% (potato flour), based on the diagrams recorded within the temperature range 20–1000°C, narrower temperature ranges of dehydration and decomposition processes were determined. In addition, the number of stages of thermal decomposition of the examined products was determined and appropriate kinetic parameters were calculated. The values of the activation energy (E a) of dehydration, frequency factor (A) and reaction order (n) were calculated from TG, DTG andT curves within the temperature range from 20 to 90°C. For potato flour the following values were obtained:E a=27.825 kJ/mol,A=1.05×105 1/s andn=2.97×10−3, for the remaining samples under investigation the activation energyE a is several dozen kJ/mol and the reaction ordern is very low. The obtained data show that the dehydration process under study is mainly associated with evaporation of water adsorbed on products and to less extent with chemical processes.