Experimental Investigation on Water Adsorption Using Laser Photoacoustic Spectroscopy and Numerical Simulations

In the present research we propose a model to assess the water vapors adsorption capacity of a SiO2 trap in the breathing circuit, aiming to reduce the loading of interfering compounds in human breath samples. In this study we used photoacoustic spectroscopy to analyze the SiO2 adsorption of interfering compounds from human breath and numerical simulations to study the flow of expired breath gas through porous media. As a result, the highest adsorption rate was achieved with a flow rate of 300 sccm, while the lowest rate was achieved with a flow rate of 600 sccm. In the procedure of H2O removal from the human breath air samples, we determined a quantity of 213 cm3 SiO2 pearls to be used for a 750 mL sampling bag, in order to keep the detection of ethylene free of H2O interference. The data from this study encourages the premise that the SiO2 trap is efficient in the reduction of interfering compounds (like water vapors) from the human breath.

Quantum Cascade Laser Photoacoustic Spectroscopy Applied to Rice Flour Analysis

In the present work we applied laser photoacoustic spectroscopy (LPAS) to the analysis of food samples. In particular, we analyzed samples of different rice flours (standard and commercial ones). For this purpose, a laboratory system based on quantum cascade laser (QCL) has been developed and characterized. After that, the LPAS spectra of all the rice samples were collected with a standard error of less than 2% of the measured value and a background signal negligible compared to the sample signals. All the experimental LPAS spectra resulted to be rich in spectral features showing clear differences between each other. The experimental spectra were then analyzed by comparison with the FT-IR transition frequency recorded in our laboratory to consent a proper assignment. Finally, to put in evidence the small differences among the various rice types, the Principal Component Analysis (PCA) was applied to the recorded LPAS spectra highlighting five different groups corresponding to the five types of samples. In conclusion, the present work demonstrated the discriminating capability of LPAS technique in the case of different types of rice flour samples.

Non-destructive methods for fruit quality evaluation

This work studies the evolution in time of several varieties of apples with application in quality storage maintenance. Two different methods were used to evaluate long-stored apples for better sorting and degradation assessment. The first method was laser photoacoustic spectroscopy for the detection of ethylene and ethanol compounds from the internal atmosphere of apples. The second method was multispectral imaging that measures the image and the spectrum combined and also can be used to address features such as ripening and external defects. The experiments showed that, the ethylene value decreases and the value of ethanol increases, which sometimes we may associate with a drift of the images toward darker tones, because the apple is slowly degrading. Non-invasive, real-time inspection can reveal when the degradation process begins, improving the capability of sorting, maintaining their quality and storability.

Monitoring of Post-Harvest Maturation Processes inside Stored Fruit Using Photoacoustic Gas Sensing Spectroscopy

Gases produced inside harvested fruit sensitively influence the continuing quality of the stored fruit and its maximum time of storability. In this work, the evolution of gaseous volatiles inside “Golden Delicious” apples were studied using CO2 laser photoacoustic spectroscopy with the aim of developing new methods for in-storage fruit quality monitoring. Studying the concentrations of volatile organic compounds generated inside “Golden Delicious” apples during storage, it was found that the concentrations of these compounds depended on the stage of maturity reached during fruit maturation and on the conditions of preservation. Numerical simulations using COMSOL Multiphysics software were used to study the conversion of ethylene to ethanol in the course of respiration processes occurring inside stored food. Experimental data obtained by means of photoacoustic spectroscopy were used to critically assess the simulation results. Using the combination of both techniques, new prospects for the development and implementation of advanced schemes of fruit storage and preservation have emerged.

The Analysis of Lead Phytotoxicity in Seeds Using CO2 Laser Photoacoustic Spectroscopy

Lead (Pb) is the most prevalent heavy metal pollutant in the natural environment. Pb is not a fundamental element for plants, but they absorb it when it is present in their environment, having no known physiological activity. The aim of our research was to evaluate the efficacy of laser photoacoustic spectroscopy as a tool to monitor changes induced by Pb in plant respiration by highlighting two molecular markers (C2H4 and CO2). To better understand Pb phytotoxicity, we monitored the plantlets evolution as well as the morphology of the root cells. Firstly, we showed that the treatment hinders the plantlet’s development. Furthermore, using laser photoacoustic spectroscopy, we found a decrease in the concentration of C2H4 and CO2 vapors measured in the respiration of treated plants. Finally, fluorescence microscopy results showed that in Pb treated plantlets, the cell roots morphology is clearly altered as compared with the untreated ones. All the results are well correlated and can help further in understanding Pb phytotoxicity.

Application of the CO2 Laser Photoacoustic Spectroscopy in Detecting Ammonia Gas (NH3) in Liver Disease Patient’s Breath

Using a CO2 laser photoacoustic spectroscopy with intracavity setup and multicomponent method we have done measurement on the ammonia, ehtylene and acetone gas concentrations in the breath of liver disease patients and in the healthy volunteers. The results of multicomponent analysis show that the average concentration of ammonia gas obtained from the breath of liver disease patients and healthy volunteers are (3.27 ± 0.75) and (1.34 ± 0.24) ppm, respectively. The highest and the lowest ammonia gas concentration of liver disease patients are 4.77 and 1.99 ppm. While, the highest and the lowest ammonia gas concentration of healthy volunteers are 1.89 and 1.08 ppm. For the ethylene and acetone concentrations, we found no significant difference between the average concentrations in the liver disease patients and in the healthy volunteers.

Design of Data Acquisition System for Green Laser Photoacoustic Spectroscopy Using Audacity Software

Research on design of data acquisition system for green laser photoacoustic spectroscopy has been done. The purpose of this research was to create and test data acquisition system for green laser photoacoustic spectroscopy. The system was created with ATR 3350iS microphone as signal detector and audacity software as data recording and processing. The testing was conducted in four phases, firstly testing the system without laser, secondly testing the system with non-modulated laser, thirdly testing the system with modulated laser without a sample, and finally testing the system with modulated laser to wood sample. The result showed that there weren not any photoacoustic signals detected in condition of without laser and with non-modulated laser. Meanwhile, in the condition of modulated laser without sample and with the sample of wood, the data acquisition system detected photoacoustic signals in the range of laser modulation frequency was 1000 – 9981 Hz.