Table 2.Ethylene efflux and sensitivity of selected fruit and vegetables . Latest GC systems have a 19-inch rack (Compact GC from Axel Semrau). The highest sensitivity can be achieved by photoacoustic spectroscopy. A laser beam (frequently used is a CO2 laser) is polarized and chopped in a specific frequency. Note that in the IUPAC system, the name ethylene is reserved for the divalent group -CH2CH2-. Below a particle size of about 100 nm, the properties of nanoparticles of gold radically change and their extremely large surface area generates high reactivity (figure 3); nanoparticles catalyse particularly the oxidation of double carbon bonds . Next to a pre-amplification stage, a synchronous detection (lock-in amplifier) is used in order to increase the signal-to-noise ratio. Climacteric fruits have a distinctive peak during the ripening process. Much of this production goes toward polyethylene, a widely used plastic containing polymer chains of ethylene units in various chain lengths.  showed very good performances for such a relatively simple sensor.  It can be produced via dehydration of ethanol with sulfuric acid or in the gas phase with aluminium oxide. However, in the studies of de Gouw et al , the EDT-300 from Sensor Sense withstands the conditions in an airplane without being negatively influenced by the strong vibrations. The transition moment integral is derived from the one-dimensional harmonic oscillator. . The size of the system is 33×27×15 cm3.  Other uses are to hasten the ripening of fruit, and as a welding gas. Following experimentation by Luckhardt, Crocker, and Carter at the University of Chicago, ethylene was used as an anesthetic. A mobile system was developed which is small, robust and sufficiently sensitive for use inside a container during transport. Mechanical parts like pumps (used in μGC and SmartGAS) can show fatigue and thereby cause a drift of the measured values or a complete failure. The advantage of measuring CO2 at the same time is quite important during ripening. For the measurement, they used a device by Sensor Sense Company. Ethylene is oxidized to produce ethylene oxide, a key raw material in the production of surfactants and detergents by ethoxylation. At €7000 the ETH1010 is in the medium-priced range and therefore the use inside fruit containers on a larger scale seems to be difficult at present. Applying in situ measurement at the point of natural ethylene generation has been hampered by the lack of portable units designed to detect ethylene at necessary resolutions of a few parts per billion. In this study, the accuracy was between 96 and 98% of 0.05–0.15 ppm C2H4 and a variation coefficient of 0.5–2%, when the calibration gas of 8 ppm C2H4 was measured after calibration. Attached on the top of the package is a Fresnel multi-lens, intended to divide the total IR radiation transmitted by the absorption cell into four and focus into the corresponding absorption zone of the thermopiles. Standard Reference Data Act. Such a sensor is not a stand-alone sensor device, owing to high cross-selectivity and poor sensitivity. In Dow et al. At 20°C, carrots produce less than 0.1 μl while kiwifruits produce 1 μl of C2H4 kg−1 h−1, but both react very sensitively to low ethylene levels. Further information about the project can be found at www.intelligentcontainer.com. We also thank Dole Fresh Fruit Europe for provision of test facilities. The electrochemical cell of the ETH1010 uses water as a reactant and has therefore lower sensitivity towards changing humidity; conversely, if the sensor is left in very low humidity and dry ambient conditions, the sensor cell will require constant monitoring and replenishment of the water in the electrolyte reservoir. Agarwal et al. )Download figureOpen in new tabDownload powerPoint, Figure 8. However, the Photovac Explorer has a small size but is quite expensive and the system is not designed for usage in container application. Also, the MOX sensor of the GC can drift, as the active surface corrodes over time. In the future, all three depicted systems will be present in the fruit supply chain. Figure 10. The inert gold does not react with most other compounds. After 5 min of heating the μPC is connected to the μ-column to inject the gas sample. Numerous hydrocarbons in ppb concentrations are negligible for optical measurement, but ammonia, ethanol and acetaldehyde can occur in concentration ranges of several ppm, and thus have to be considered as interfering in the IR measurements of ethylene. Figure 1. The two peaks after the injection peak were assigned according to the measurements of the humidity sensor. We depicted these three systems, because they are showing good overall performances and the prices are in a reasonable range.  Other technologies employed for the production of ethylene include oxidative coupling of methane, Fischer-Tropsch synthesis, methanol-to-olefins (MTO), and catalytic dehydrogenation. The required selectivity is achieved by different techniques. In the future, all three systems can be further improved. (Online version in colour. Its size is 39×27×15 cm3. (a) Ethylene concentrations along the (apple) fruit supply chain, measured in situ in an open gas system with a portable ethylene unit and (b) example of sampling on the sorting belt . Source: HITRAN . All rights reserved. a multi-spectral measurement has to be performed. Filter wavelengths for ethylene at 10.6 μm, ethanol at 3.46 μm, ammonia at 9.7 μm and a reference channel at 3.95 μm have been chosen for the four-element thermopile array. Go To: Top, Vibrational and/or electronic energy levels, Notes, Shimanouchi, 1972 The lifespan of the MOX sensor and the IR source must be investigated in long-term field tests. The selection rule for IR activity is that there is a change in the dipole moment of the vibrational mode of the molecule. Ethylene is a fundamental ligand in transition metal alkene complexes. This problem must be solved before the detection limit of this device can reach this lower level. An auto-zero function provides a fresh zero automatically when necessary, using the built-in potassium permanganate column . Table 1.Physiological effects of exogenous ethylene on fruit and vegetables as dependent on their climacteric classification . Data Program, but require an annual fee to access. The detection limit (3σ) of the SmartGAS sensor is 20 ppm for a measurement time (integration time) of 15 s. The SmartGAS system uses a two-channel approach, one channel for the ethylene detection and the other channel for CO2 measurements. With the dimensions of 40.0×2.0×0.9 mm3 for each of the eight channels the μPC contains 191 mg of CSII. Less than 1 part per million (ppm) by volume of ethylene gas is sufficient to trigger the ripening process of climacteric fruit . Besides CO2 and O2, ethylene is the most important gas to be monitored and controlled in the supply chain of fruits [4–6]. The distance between the output focus of the White cell and the detection module depends on the tolerances of the focal length of the Fresnel multi-lens. Besides the column length and the stationary phase, the temperature is also an important issue. However, by that time, the name ethylene was deeply entrenched, and it remains in wide use today, especially in the chemical industry. All rights reserved. However, tests with humidified synthetic air showed that the impact of this effect is not very significant to the measurement. In the United States and Europe, approximately 90% of ethylene is used to produce ethylene oxide, ethylene dichloride, ethylbenzene and polyethylene. Nevertheless, use of the name ethylene for H2C=CH2 is still prevalent among chemists in North America. The optical path, i.e. Ethylene is separated from the resulting mixture by repeated compression and distillation. Current developments were highlighted in the previous section in addition to the earlier overview by Cristescu . First tests showed the feasibility of such combination and promising improvements of sensitivity [48,49]. Methods for normal phonon mode determination N.B.! Several measuring methods for the detection of ethylene have been investigated in the past. This is sufficient for measurement in a container or CA store. The first column is a capillary column that is typically used. In some climacteric fruit like apples, the application of 1-MCP (1-methylcyclopropene) at harvest, blocking the ethylene receptor, is a possibility to reduce subsequent ethylene efflux, postpone ripening and extend storability . These fruits are shipped after such de-greening, e.g. Enter your email address below and we will send you your username, If the address matches an existing account you will receive an email with instructions to retrieve your username, Institute for Microsensors, -actuators and -systems (IMSAS), University of Bremen, Otto-Hahn-Allee NW1, Bremen 28359, Germany, Microsystems Center Bremen (MCB), Bremen, Germany, Bremen Research Cluster for Dynamics in Logistics (LogDynamics), Bremen, Germany, Fraunhofer Institute for Physical Measurement Techniques (IPM), Freiburg, Germany, INRES—Horticultural Science, University of Bonn, Bonn, Germany, Department of Microsystems Engineering, University of Freiburg, Freiburg, Germany. The accumulation of the ripening gas ethylene may lead to premature ripening of fruits and vegetables or their decay (table 1) with few exceptions. The main disadvantage is the price (ca € 30 000 for the Sensor Sense EDT-300 with a sensitivity of 0.3 ppb for ±2σ [19,24]; €20 000 for Gasera F10 with a sensitivity of only 800 ppb ). An example is the system CompactGC by Axel Semrau. Scanning electron micrographs of gold nanoparticles: (a) magnification ×20k; (b) ×100k. IR-active Raman-active IR-active Pb 2 Pb 1 O p O t P a b c Isolated TO 4 group IR-active Raman-active Crystal: Pb 3(PO 4) 2, R3m. Climacteric fruit can hence be the first major source of ethylene in all compartments along the food chain from the ship hull, regional distribution centre, wholesale market, receiving area, storage and display shelf in the supermarket. A new, improved SmartGAS NDIR system will be available soon. . The systems themselves as well as the peripheral equipment potentially necessary for operation of such sensor systems in a container will be discussed, because there are some important issues with regard to practicability. In the following sections, measurement principles and systems actually used in logistic processes will be discussed. One of the latest developments is presented in Sun et al. At present, only a prototype is available. First tests were performed for the communication between the computation unit of the so-called ‘Intelligent Container’  and the sensor device. Most common in this field is the use of SnO2 as active surface. The photoacoustic amplitude rises with the concentration of the specific gas component. Ethylene analyser. It consists of a substrate chip with an array of 2×2 thermopile elements based on silicon technology that is attached to the base of the package.
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