In the present work published in the journal ACS Applied Nano Materials, graphite carbon black-based laser desorption ionization- mass spectroscopy (GCBLDI-MS) is reported as one of a kind of surface assisted LDI-MS technique. Here, detection of taste and odor of chemical compounds was possible in a simplistic manner.
Study: Laser Desorption Ionization–Mass Spectrometry with Graphite Carbon Black Nanoparticles for Simultaneous Detection of Taste- and Odor-Active Compounds. Image Credit: nadianb/Shutterstock.com
Recognition of taste and odor food by humans is necessary for the analysis, quantitative evaluation and digitization of the flavor quality of food.
Current techniques of chemical component evaluation such as liquid chromatography or gas chromatography in coupling with mass spectroscopy require tedious sample preparation methods, which may result in loss of exact flavor of food.
A technique called matrix-assisted laser desorption ionization-mass spectroscopy (MALDI-MS) is usually used to detect chemical molecules through irradiating the target plate by ultraviolet laser.
The disadvantage with this technique is the occurrence of masking noise when detecting low mass range.
Nanostructured materials having low heat capacity and high conductivity offers another technique called surface assisted LDI (SALDI)-MS, which overcomes the drawback of MALDI-MS.
The present work reports graphite carbon black (GCB) as nanostructures for SALDI-MS. GCB are nanoparticles consisting of multilayered sheets of carbon atoms connected in sp2 hybridization.
GCB is reported to show low heat capacity, high conductivity and has characteristics to adsorb a variety of compounds. These properties of GCB are utilized in SALDI-MS for simultaneous detection of taste and odor, providing a platform for flavor scanning.
GCBLDI-MS exhibited reduced noise signals on detecting low molecular mass compared to that obtained from other MALDI-MS.
Detection of Volatile Compounds by Nanostructured GCBLDI-MS
An ionization platform of GCB nanoparticles was used in both negative as well as positive modes.
All types of volatile compounds tested in positive and negative mode, with the exception of ethyl ester in negative mode was detected by GCBLDI-MS.
The detection of volatile compounds by carbon-based matrices is a novelty of this work as previous reports were only limited to nonvolatile compounds.
It was observed in the study that the detection of carbon compounds by GCBLDI-MS, the detected ion intensities decreased with the decrease in the number of carbon per functional group.
The minimum carbon number of each carbon functional group required for the detection was C12 for ethyl esters and alcohols, C10 for carboxylic acids and C14 for aldehydes, all at different vapor pressure values of 7.44 * 10-3, 2.09 * 10-3, 3.55 * 10-3 and 6.39 * 10-3 Torr, respectively.
In addition, the adsorption of volatile compounds over GCB is through non-interactive van der Waals intermolecular forces.
Ionization Process in GCBLDI-MS
The total ionization process, Ji, could be categorized into two factors, Jv, the rate of desorption and I, the ionization efficiency of the molecules and is represented by the formula, Ji = IJv.
The ionization efficiency, I, is associated with proton affinity or gas-phase acidity. In addition, Jv is associated with the rate of desorption or vaporization.
Generally, for desorption, the LDI ions are placed in a vacuum for the desorption of the analyte.
Advantages of GCBLDI-MS
Compared to the previously reported LDI-MS methods, GCBLDI-MS is better since it is rapid and simple. It provides a direct analysis of samples without any requirement of sample preparation.
This method is extremely beneficial for the direct detection of compounds ina volatile state where other methods require various intermittent steps of sample preparations.
It was reported that the flavor chemicals with a vapor pressure less than ~7.44 * 10-3 Torr could be detected through GCBLDI-MS.
This work exhibited that the GCBLDI-MS could detect taste and odor of compounds without any requirement of sample purification.
GCBLDI-MS was found successful in detecting nonvolatile amino acids and volatile ethyl esters, fatty acids, alcohols and aldehydes.
Future Perspectives of GCBLDI-MS
Detection of highly volatile chemicals could be achieved through further surface modifications of GCB or through film coatings that could improve the chemical adsorption.
The performance of GCBLDI-MS could be further enhanced when used with advanced technology such as trapped ion mobility spectroscopy coupled with time of flight mass spectroscopy (TIMS-TOF-MS).
This could enhance the resolution of GCBLDI-MS and help detect complex taste and odor compositions of food; in addition, discrimination of isomers could also be possible.
Thus, this work reports a novel GCBLDI-MS process for the instant determination of the taste and odor of the food for the digitization of food quality. Further, evaluation of palatability of food products could be performed.
Continue reading: New Perspectives on Nanoparticle Presence in Food
Tanaka, M., Arima, K., Takeshita, T., Kunitake, Y., Ohno, N., Imamura, M., and Matsui. T., (2022) Laser Desorption Ionization-Mass Spectroscopy with Graphite Carbon Black Nanoparticles for Simultaneous Detection of Taste and Odor-Active Compounds, ACS Applied Nano Materials. Available at: https://pubs.acs.org/doi/10.1021/acsanm.1c03890.
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