Research

984 KiB

Open AccessArticle

Determination of the Mineral Composition and Toxic Element Contents of Propolis by Near Infrared Spectroscopy

by M. Inmaculada González-Martín, Olga Escuredo, Isabel Revilla, Ana M. Vivar-Quintana, M. Carmen Coello, Carlos Palacios Riocerezo and Guillermo Wells Moncada

Sensors 2015, 15(11), 27854-27868; https://doi.org/10.3390/s151127854 - 03 Nov 2015

Cited by 42 | Viewed by 6060

Abstract

The potential of near infrared spectroscopy (NIR) with remote reflectance fiber-optic probes for determining the mineral composition of propolis was evaluated. This technology allows direct measurements without prior sample treatment. Ninety one samples of propolis were collected in Chile (Bio-Bio region) and Spain [...] Read more.

The potential of near infrared spectroscopy (NIR) with remote reflectance fiber-optic probes for determining the mineral composition of propolis was evaluated. This technology allows direct measurements without prior sample treatment. Ninety one samples of propolis were collected in Chile (Bio-Bio region) and Spain (Castilla-León and Galicia regions). The minerals measured were aluminum, calcium, iron, potassium, magnesium, phosphorus, and some potentially toxic trace elements such as zinc, chromium, nickel, copper and lead. The modified partial least squares (MPLS) regression method was used to develop the NIR calibration model. The determination coefficient (R²) and root mean square error of prediction (RMSEP) obtained for aluminum (0.79, 53), calcium (0.83, 94), iron (0.69, 134) potassium (0.95, 117), magnesium (0.70, 99), phosphorus (0.94, 24) zinc (0.87, 10) chromium (0.48, 0.6) nickel (0.52, 0.7) copper (0.64, 0.9) and lead (0.70, 2) in ppm. The results demonstrated that the capacity for prediction can be considered good for wide ranges of potassium, phosphorus and zinc concentrations, and acceptable for aluminum, calcium, magnesium, iron and lead. This indicated that the NIR method is comparable to chemical methods. The method is of interest in the rapid prediction of potentially toxic elements in propolis before consumption. Full article

(This article belongs to the Special Issue Chemical Sensors based on In Situ Spectroscopy)

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1583 KiB

Open AccessArticle

Nitric Oxide Isotopic Analyzer Based on a Compact Dual-Modulation Faraday Rotation Spectrometer

by Eric Zhang, Stacey Huang, Qixing Ji, Michael Silvernagel, Yin Wang, Bess Ward, Daniel Sigman and Gerard Wysocki

Sensors 2015, 15(10), 25992-26008; https://doi.org/10.3390/s151025992 - 14 Oct 2015

Cited by 11 | Viewed by 6841

Abstract

We have developed a transportable spectroscopic nitrogen isotopic analyzer. The spectrometer is based on dual-modulation Faraday rotation spectroscopy of nitric oxide isotopologues with near shot-noise limited performance and baseline-free operation. Noise analysis indicates minor isotope (¹⁵NO) detection sensitivity of 0.36 ppbv·Hz [...] Read more.

We have developed a transportable spectroscopic nitrogen isotopic analyzer. The spectrometer is based on dual-modulation Faraday rotation spectroscopy of nitric oxide isotopologues with near shot-noise limited performance and baseline-free operation. Noise analysis indicates minor isotope (¹⁵NO) detection sensitivity of 0.36 ppbv·Hz^−1/2, corresponding to noise-equivalent Faraday rotation angle (NEA) of 1.31 × 10⁻⁸ rad·Hz^−1/2 and noise-equivalent absorbance (αL)_min of 6.27 × 10⁻⁸ Hz^−1/2. White-noise limited performance at 2.8× the shot-noise limit is observed up to ~1000 s, allowing reliable calibration and sample measurement within the drift-free interval of the spectrometer. Integration with wet-chemistry based on acidic vanadium(III) enables conversion of aqueous nitrate/nitrite samples to gaseous NO for total nitrogen isotope analysis. Isotopic ratiometry is accomplished via time-multiplexed measurements of two NO isotope transitions. For 5 μmol potassium nitrate samples, the instrument consistently yields ratiometric precision below 0.3‰, thus demonstrating potential as an in situ diagnostic tool for environmental nitrogen cycle studies. Full article

(This article belongs to the Special Issue Chemical Sensors based on In Situ Spectroscopy)

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4254 KiB

Open AccessArticle

A Wireless Multi-Sensor Dielectric Impedance Spectroscopy Platform

by Seyed Alireza Ghaffari, William-O. Caron, Mathilde Loubier, Maxime Rioux, Jeff Viens, Benoit Gosselin and Younes Messaddeq

Sensors 2015, 15(9), 23572-23588; https://doi.org/10.3390/s150923572 - 17 Sep 2015

Cited by 8 | Viewed by 8027

Abstract

This paper describes the development of a low-cost, miniaturized, multiplexed, and connected platform for dielectric impedance spectroscopy (DIS), designed for in situ measurements and adapted to wireless network architectures. The platform has been tested and used as a DIS sensor node on ZigBee [...] Read more.

This paper describes the development of a low-cost, miniaturized, multiplexed, and connected platform for dielectric impedance spectroscopy (DIS), designed for in situ measurements and adapted to wireless network architectures. The platform has been tested and used as a DIS sensor node on ZigBee mesh and was able to interface up to three DIS sensors at the same time and relay the information through the network for data analysis and storage. The system is built from low-cost commercial microelectronics components, performs dielectric spectroscopy ranging from 5 kHz to 100 kHz, and benefits from an on-the-fly calibration system that makes sensor calibration easy. The paper describes the microelectronics design, the Nyquist impedance response, the measurement sensitivity and accuracy, and the testing of the platform for in situ dielectric impedance spectroscopy applications pertaining to fertilizer sensing, water quality sensing, and touch sensing. Full article

(This article belongs to the Special Issue Chemical Sensors based on In Situ Spectroscopy)

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1376 KiB

Open AccessArticle

Improving the Detection Limit in a Capillary Raman System for In Situ Gas Analysis by Means of Fluorescence Reduction

by Simone Rupp, Andreas Off, Hendrik Seitz-Moskaliuk, Timothy M. James and Helmut H. Telle

Sensors 2015, 15(9), 23110-23125; https://doi.org/10.3390/s150923110 - 11 Sep 2015

Cited by 17 | Viewed by 7646

Abstract

Raman spectroscopy for low-pressure or trace gas analysis is rather challenging, in particular in process control applications requiring trace detection and real-time response; in general, enhancement techniques are required. One possible enhancement approach which enjoys increasing popularity makes use of an internally-reflective capillary [...] Read more.

Raman spectroscopy for low-pressure or trace gas analysis is rather challenging, in particular in process control applications requiring trace detection and real-time response; in general, enhancement techniques are required. One possible enhancement approach which enjoys increasing popularity makes use of an internally-reflective capillary as the gas cell. However, in the majority of cases, such capillary systems were often limited in their achievable sensitivity by a significant fluorescence background, which is generated as a consequence of interactions between the laser light and optical glass components in the setup. In order to understand and counteract these problems we have investigated a range of fluorescence-reducing measures, including the rearrangement of optical elements, and the replacement of glass components—including the capillary itself—by metal alternatives. These studies now have led to a capillary setup in which fluorescence is practically eliminated and substantial signal enhancement over standard Raman setups is achieved. With this improved (prototype) setup, detection limits of well below 1 mbar could be obtained in sub-second acquisition times, demonstrating the potential of capillary Raman spectroscopy for real-time, in situ gas sensing and process control applications, down to trace level concentrations. Full article

(This article belongs to the Special Issue Chemical Sensors based on In Situ Spectroscopy)

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6392 KiB

Open AccessArticle

New Opportunities in Mid-Infrared Emission Control

by Peter Geiser

Sensors 2015, 15(9), 22724-22736; https://doi.org/10.3390/s150922724 - 09 Sep 2015

Cited by 24 | Viewed by 9147

Abstract

Tunable laser absorption spectroscopy (TLAS) has been well accepted as a preferred measurement technique for many industrial applications in recent years, especially for in situ applications. Previously, mainly near-infrared lasers have been used in TLAS sensors. The advent of compact mid-infrared light sources, [...] Read more.

Tunable laser absorption spectroscopy (TLAS) has been well accepted as a preferred measurement technique for many industrial applications in recent years, especially for in situ applications. Previously, mainly near-infrared lasers have been used in TLAS sensors. The advent of compact mid-infrared light sources, like quantum cascade lasers and interband cascade lasers, has made it possible to detect gases with better sensitivity by utilizing fundamental absorption bands and to measure species that do not have any absorption lines in the near-infrared spectral region. This technological advancement has allowed developing new sensors for gases, such as nitric oxide and sulfur dioxide, for industrial applications. Detection limits of better than 1 ppm·m for nitric oxide and better than 10 ppm·m for sulfur dioxide are demonstrated in field experiments. Full article

(This article belongs to the Special Issue Chemical Sensors based on In Situ Spectroscopy)

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2393 KiB

Open AccessArticle

Field Test of a Remote Multi-Path CLaDS Methane Sensor

by Genevieve Plant, Michal Nikodem, Phil Mulhall, Ruth K. Varner, David Sonnenfroh and Gerard Wysocki

Sensors 2015, 15(9), 21315-21326; https://doi.org/10.3390/s150921315 - 28 Aug 2015

Cited by 26 | Viewed by 5949

Abstract

Existing technologies for quantifying methane emissions are often limited to single point sensors, making large area environmental observations challenging. We demonstrate the operation of a remote, multi-path system using Chirped Laser Dispersion Spectroscopy (CLaDS) for quantification of atmospheric methane concentrations over extended areas, [...] Read more.

Existing technologies for quantifying methane emissions are often limited to single point sensors, making large area environmental observations challenging. We demonstrate the operation of a remote, multi-path system using Chirped Laser Dispersion Spectroscopy (CLaDS) for quantification of atmospheric methane concentrations over extended areas, a technology that shows potential for monitoring emissions from wetlands. Full article

(This article belongs to the Special Issue Chemical Sensors based on In Situ Spectroscopy)

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1009 KiB

Open AccessArticle

Application of Visible and Near-Infrared Hyperspectral Imaging to Determine Soluble Protein Content in Oilseed Rape Leaves

by Chu Zhang, Fei Liu, Wenwen Kong and Yong He

Sensors 2015, 15(7), 16576-16588; https://doi.org/10.3390/s150716576 - 09 Jul 2015

Cited by 74 | Viewed by 7622

Abstract

Visible and near-infrared hyperspectral imaging covering spectral range of 380–1030 nm as a rapid and non-destructive method was applied to estimate the soluble protein content of oilseed rape leaves. Average spectrum (500–900 nm) of the region of interest (ROI) of each sample was [...] Read more.

Visible and near-infrared hyperspectral imaging covering spectral range of 380–1030 nm as a rapid and non-destructive method was applied to estimate the soluble protein content of oilseed rape leaves. Average spectrum (500–900 nm) of the region of interest (ROI) of each sample was extracted, and four samples out of 128 samples were defined as outliers by Monte Carlo-partial least squares (MCPLS). Partial least squares (PLS) model using full spectra obtained dependable performance with the correlation coefficient (r_p) of 0.9441, root mean square error of prediction (RMSEP) of 0.1658 mg/g and residual prediction deviation (RPD) of 2.98. The weighted regression coefficient (Bw), successive projections algorithm (SPA) and genetic algorithm-partial least squares (GAPLS) selected 18, 15, and 16 sensitive wavelengths, respectively. SPA-PLS model obtained the best performance with r_p of 0.9554, RMSEP of 0.1538 mg/g and RPD of 3.25. Distribution of protein content within the rape leaves were visualized and mapped on the basis of the SPA-PLS model. The overall results indicated that hyperspectral imaging could be used to determine and visualize the soluble protein content of rape leaves. Full article

(This article belongs to the Special Issue Chemical Sensors based on In Situ Spectroscopy)

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2522 KiB

Open AccessArticle

Application of Cavity Enhanced Absorption Spectroscopy to the Detection of Nitric Oxide, Carbonyl Sulphide, and Ethane—Breath Biomarkers of Serious Diseases

by Jacek Wojtas

Sensors 2015, 15(6), 14356-14369; https://doi.org/10.3390/s150614356 - 17 Jun 2015

Cited by 34 | Viewed by 7020

Abstract

The paper presents one of the laser absorption spectroscopy techniques as an effective tool for sensitive analysis of trace gas species in human breath. Characterization of nitric oxide, carbonyl sulphide and ethane, and the selection of their absorption lines are described. Experiments with [...] Read more.

The paper presents one of the laser absorption spectroscopy techniques as an effective tool for sensitive analysis of trace gas species in human breath. Characterization of nitric oxide, carbonyl sulphide and ethane, and the selection of their absorption lines are described. Experiments with some biomarkers showed that detection of pathogenic changes at the molecular level is possible using this technique. Thanks to cavity enhanced spectroscopy application, detection limits at the ppb-level and short measurements time (<3 s) were achieved. Absorption lines of reference samples of the selected volatile biomarkers were probed using a distributed feedback quantum cascade laser and a tunable laser system consisting of an optical parametric oscillator and difference frequency generator. Setup using the first source provided a detection limit of 30 ppb for nitric oxide and 250 ppb for carbonyl sulphide. During experiments employing a second laser, detection limits of 0.9 ppb and 0.3 ppb were obtained for carbonyl sulphide and ethane, respectively. The conducted experiments show that this type of diagnosis would significantly increase chances for effective therapy of some diseases. Additionally, it offers non-invasive and real time measurements, high sensitivity and selectivity as well as minimizing discomfort for patients. For that reason, such sensors can be used in screening for early detection of serious diseases. Full article

(This article belongs to the Special Issue Chemical Sensors based on In Situ Spectroscopy)

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5935 KiB

Open AccessArticle

Investigation of Two Novel Approaches for Detection of Sulfate Ion and Methane Dissolved in Sediment Pore Water Using Raman Spectroscopy

by Zengfeng Du, Jing Chen, Wangquan Ye, Jinjia Guo, Xin Zhang and Ronger Zheng

Sensors 2015, 15(6), 12377-12388; https://doi.org/10.3390/s150612377 - 26 May 2015

Cited by 16 | Viewed by 8014

Abstract

The levels of dissolved sulfate and methane are crucial indicators in the geochemical analysis of pore water. Compositional analysis of pore water samples obtained from sea trials was conducted using Raman spectroscopy. It was found that the concentration of SO₄²⁻ in [...] Read more.

The levels of dissolved sulfate and methane are crucial indicators in the geochemical analysis of pore water. Compositional analysis of pore water samples obtained from sea trials was conducted using Raman spectroscopy. It was found that the concentration of SO₄²⁻ in pore water samples decreases as the depth increases, while the expected Raman signal of methane has not been observed. A possible reason for this is that the methane escaped after sampling and the remaining concentration of methane is too low to be detected. To find more effective ways to analyze the composition of pore water, two novel approaches are proposed. One is based on Liquid Core Optical Fiber (LCOF) for detection of SO₄²⁻. The other one is an enrichment process for the detection of CH₄. With the aid of LCOF, the Raman signal of SO₄²⁻ is found to be enhanced over 10 times compared to that obtained by a conventional Raman setup. The enrichment process is also found to be effective in the investigation to the prepared sample of methane dissolved in water. By CCl₄ extraction, methane at a concentration below 1.14 mmol/L has been detected by conventional Raman spectroscopy. All the obtained results suggest that the approach proposed in this paper has great potential to be developed as a sensor for SO₄²⁻ and CH₄ detection in pore water. Full article

(This article belongs to the Special Issue Chemical Sensors based on In Situ Spectroscopy)

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2755 KiB

Open AccessArticle

A Online NIR Sensor for the Pilot-Scale Extraction Process in Fructus Aurantii Coupled with Single and Ensemble Methods

by Xiaoning Pan, Yang Li, Zhisheng Wu, Qiao Zhang, Zhou Zheng, Xinyuan Shi and Yanjiang Qiao

Sensors 2015, 15(4), 8749-8763; https://doi.org/10.3390/s150408749 - 14 Apr 2015

Cited by 13 | Viewed by 6873

Abstract

Model performance of the partial least squares method (PLS) alone and bagging-PLS was investigated in online near-infrared (NIR) sensor monitoring of pilot-scale extraction process in Fructus aurantii. High-performance liquid chromatography (HPLC) was used as a reference method to identify the active pharmaceutical [...] Read more.

Model performance of the partial least squares method (PLS) alone and bagging-PLS was investigated in online near-infrared (NIR) sensor monitoring of pilot-scale extraction process in Fructus aurantii. High-performance liquid chromatography (HPLC) was used as a reference method to identify the active pharmaceutical ingredients: naringin, hesperidin and neohesperidin. Several preprocessing methods and synergy interval partial least squares (SiPLS) and moving window partial least squares (MWPLS) variable selection methods were compared. Single quantification models (PLS) and ensemble methods combined with partial least squares (bagging-PLS) were developed for quantitative analysis of naringin, hesperidin and neohesperidin. SiPLS was compared to SiPLS combined with bagging-PLS. Final results showed the root mean square error of prediction (RMSEP) of bagging-PLS to be lower than that of PLS regression alone. For this reason, an ensemble method of online NIR sensor is here proposed as a means of monitoring the pilot-scale extraction process in Fructus aurantii, which may also constitute a suitable strategy for online NIR monitoring of CHM. Full article

(This article belongs to the Special Issue Chemical Sensors based on In Situ Spectroscopy)

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