Available online at www.sciencedirect.com
Procedia Engineering 47 (2012) 486 – 489
Proc. Eurosensors XXVI, September 9-12, 2012, Kraków, Poland
Gas Chromatograph Based on Packed μGC-Columns and μ-Preconcentrator Devices for Ethylene Detection in Fruit Logistic Applications Adam Sklorza*, Steffen Janßen, Walter Lang Institute for Microsensors, -actuators and –systems (IMSAS), University of Bremen, 28359 Bremen,Germany
Abstract
A miniaturised preconcentrator device (μPCD) filled with Carbosieve S-II was coupled with a miniaturised gas chromatograph (μGC) and was tested with focus on ethylene gas measurement. The application of the μPCD results in an increase of the system sensitivity by a factor of 23 from 140 ppmv to 6 ppmv using an ethylene detector based on a metal oxide sensor. © 2012 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Symposium Cracoviense © 2012 Published by Elsevier Ltd. Sp. z.o.o. Open access under CC BY-NC-ND license. Keywords: preconcentrator; gas chromatography; μGC; ethylene detection; ethylene sensor; fruit logistics; intelligent container;
1. Introduction Sensor and communication technologies as well as new logistic approaches are in the research focus of the cluster project “the intelligent container” (www.intelligentcontainer.com). The main goal is the development and application of systems which provide an autonomous quality monitoring of perishable goods and thus help to prevent transport losses in the logistic chain. New measurement systems are needed to realize approaches like the dynamic FEFO (first expired – first out) using dynamic shelf life calculations to estimate the remaining quality of food. For this purpose different ambience parameters influencing the quality of goods have to be measured and used in calculations [1]. This provides reduction of losses, a better logistic distribution and transport planning as well as an assignment of responsibilities in the transport chain.
* Corresponding author. Tel.: +49(0)421 218 62643; fax: +49(0)421 218 9862643 E-mail address:
[email protected]
1877-7058 © 2012 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Symposium Cracoviense Sp. z.o.o. Open access under CC BY-NC-ND license. doi:10.1016/j.proeng.2012.09.190
Adam Sklorz et al. / Procedia Engineering 47 (2012) 486 – 489
For many goods the measurement of the ambience temperature and humidity is sufficient for shelf life estimation but not for climacterics fruits. Because of the biological activity of fruits additionally the ethylene concentration in ambience has to be taken into account [2]. This is a ripeness indicator on one hand and a ripeness accelerator on the other. For this reason systems are needed which are able to measure ethylene concentration within the low ppmv or better within the ppbv range selectively. A miniaturized gas chromatograph (μGC) for this purpose was already presented [3]. In this paper the combination of this μGC with a miniaturized preconcentrator device (μPC) for sensitivity enhancement to ethylene is described. 2. Methods The construction and behaviour of the μGC and its chromatographic abilities were described in [3]. The μPC device (see fig 1a) is based on previous works [4]. It has an edge size of 18.5 mm x 9.3 mm x 1.26 mm and was fabricated using a silicon/Pyrex stack. In the silicon 8 parallel adsorption channels were integrated. At the back side of the preconcentrator a 50 : platinum heater was placed for application of the desorption temperature. The preconcentrator was filled with Carbosieve S-II as adsorption material and was integrated into aluminium housing with valves for bypassing and electrical connections for the heater (see fig 1b). Its housing was connected pneumatically to the μGC (see fig 1c). (a)
(b)
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Fig. 1: Silicon based μPC (a), μPCD device integrated into pneumatic housing (b) and a μGC with the μPC device (c)
For experiments the setup outlined in figure 2 was used. The μGC including the preconcentrator was coupled with two mass flow controllers (MFC) at its sample input. The MFC were supplied by a bottle with synthetic air and a bottle with ethylene in synthetic air. At the pneumatic output of the μGC a flow meter was connected to cross check gas tightness. The entire setup was computer controlled using a DAQ-Device and a LabView implementation. Each measurement run consisted of three measurement steps. Step 1: During the sampling / preconcentration step the GC-column was bypassed and the gas sample was switched to the adsorption channels of the μPC. The temperature of the μPC was hold at room temperature. A sample gas flow with a certain ethylene concentration and a flow rate of 10 ml/min was activated. After 10 min the sample stream was set to bypass of the μPC. Step 2: The second step was used to initialise the measurement. During this synthetic air with a flow rate of 20 ml/min was activated and switched to the GC-Column which was hold at a temperature of 45°C. Step 3: The last was the measurement step. At its beginning the measurement was started and the μPC was heated up to 200°C for one minute. Then the carrier synthetic air gas stream was switched on the adsorption channels of the μPC. The flow and the temperature were held constant for one minute and subsequently the μPC heater was turned off and the μPC was again bypassed. For a quantitative analysis of the preconcentration effect two different μPC variations were applied. For one measurement series the preconcentrator was filled with 8
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mg of Carbosieve S-II. For the second measurement series the μPC was used without adsorption material. In that case the entire internal volume of the device was used as a sampling and injection volume.
Fig. 2: Measurement setup used for characterisation of the μPC combined with the μGC. The used detector was based on a SnO2 gas sensor and a humidity / temperature sensor
3. Results Figure 3a shows two example chromatograms which were achieved using the setup described above for both cases: A μPC with Carbosieve S-II and an empty μPC. In the related measurements an ethylene sample concentration of 500 ppmv was used. The effect of the ethylene preconcentration can be clearly seen. The ethylene peak maximum achieved using adsorption material is by the factor 16 higher than the peak achieved without adsorption material. Additionally two more peaks appear when using Carbosieve S-II. One peak is caused by water which is also adsorbed by the Carbosieve S-II and desorbed together with the ethylene. This peak can be compensated using a humidity sensor which is integrated in the SnO2 ethylene detector in the setup (see fig 3b). (a) (b) 1
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Fig.3: Chromatograms achieved with a μPC with and without Carbosieve S-II as adsorption material for 500 ppmv ethylene in synthetic air (a). Humidity compensated chromatogram based on the left hand graph and humidity sensor delivered by the used ethylene detector (b)
The very first peak in figure 3a and figure 3b is related to an unknown gas. It can be assumed that this gas is CO. The indicator for this is its short retention time and its appearance only for thermal desorption temperatures above 150 °C and the presence of synthetic air in the device.
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Figure 4a shows the comparison between the ethylene peak areas achieved using the μPC with and without Carbosieve S-II for different ethylene sample concentrations. The application of the empty μPC results in a very flat relation. For this case an ethylene measurement resolution of 142 ppmv is achieved. This resolution is increased to 6 ppmv if the μPC is filled with the adsorption material Carbosieve S-II. The resulting preconcentration factor defined as the ratio of the peak areas achieved with the filled and the empty μPC is about 23. The preconcentration factor PCF defined as the ration of the peak maximum achieved with the filled and the empty μPC is about 16 (see fig 4b). (a)
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Fig. 4: Ethylene peak area versus ethylene input concentration for μPC with and without Carbosieve S-II (a). Resulting preconcentration factor PCF related to the peak maximum (b)
4. Conclusion In this paper the application of a micro preconcentrator with a miniaturized chromatograph for ethylene detection in fruit logistic applications was described. The μPC device was filled with 8 mg of Carbosieve S-II as adsorption material. Measurement results showed an increase of the ethylene related chromatographic peak maximum by the factor of 16 when using the μPC with adsorption material. The achieved preconcentration factor referred to the ethylene peak area is about 23. The measurement resolution was increased from 142 ppmv to 6 ppmv which should be sufficient for fruit logistic applications. Acknowledgements This research project ('The Intelligent Container') is supported by the Federal Ministry of Education and Research (BMBF), Germany, under reference number 01IA10001. References [1] C. Amador et al. Application of RFID technologies in the temperature mapping of the pineapple supply chain. Sens. Instrum. Food Qual. Saf. 2009; 3:26-8. [2] Wild Y et al. Containerhandbook. Berlin: GDV German Insurance Association; 2005. [3] Sklorz A, Janßen S, Lang W. Application of a Miniaturised Packed Gas Chromatography Column and a SnO2 Gas Detector for Analysis of Low Molecular Weight Hydrocarbons with Focus on Ethylene Detection. Sens. Actuators B 2012: in press, accepted manuscript, 10.1016/j.snb.2011.12.110. [4] Alamin Dow AB, Lang W. A micromachined preconcentrator for ethylene monitoring system. Sens. Actuators, B 2010; 151: 304-4.
