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Macroscopic and microscopic spatially-resolved analysis of food contaminants and constituents using laser-ablation electrospray ionization mass spectrometry imaging.

Nielen MW, van Beek TA - Anal Bioanal Chem (2014)

Bottom Line: However, according to three-dimensional LAESI-MSI the penetration depth of imazalil into the peel has significant local variation.Ion maps of different plant alkaloids on ergot bodies from rye reveal co-localization in accordance with expectations.It is envisaged that LAESI-MSI will contribute to future research in food science, agriforensics, and plant metabolomics.

View Article: PubMed Central - PubMed

Affiliation: RIKILT Wageningen UR, P.O. Box 230, 6700 AE, Wageningen, The Netherlands, michel.nielen@wur.nl.

ABSTRACT
Laser-ablation electrospray ionization (LAESI) mass spectrometry imaging (MSI) does not require very flat surfaces, high-precision sample preparation, or the addition of matrix. Because of these features, LAESI-MSI may be the method of choice for spatially-resolved food analysis. In this work, LAESI time-of-flight MSI was investigated for macroscopic and microscopic imaging of pesticides, mycotoxins, and plant metabolites on rose leaves, orange and lemon fruit, ergot bodies, cherry tomatoes, and maize kernels. Accurate mass ion-map data were acquired at sampling locations with an x-y center-to-center distance of 0.2-1.0 mm and were superimposed onto co-registered optical images. The spatially-resolved ion maps of pesticides on rose leaves suggest co-application of registered and banned pesticides. Ion maps of the fungicide imazalil reveal that this compound is only localized on the peel of citrus fruit. However, according to three-dimensional LAESI-MSI the penetration depth of imazalil into the peel has significant local variation. Ion maps of different plant alkaloids on ergot bodies from rye reveal co-localization in accordance with expectations. The feasibility of using untargeted MSI for food analysis was revealed by ion maps of plant metabolites in cherry tomatoes and maize-kernel slices. For tomatoes, traveling-wave ion mobility (TWIM) was used to discriminate between different lycoperoside glycoalkaloid isomers; for maize quadrupole time-of-flight tandem mass spectrometry (MS-MS) was successfully used to elucidate the structure of a localized unknown. It is envisaged that LAESI-MSI will contribute to future research in food science, agriforensics, and plant metabolomics.

Show MeSH
Positive-ion LAESI-TOF-MSI accurate ion maps of (a) m/z 268.142 (±5 mDa), (b) m/z 326.186 (±5 mDa), (c) m/z 368.195 (±5 mDa), (d) m/z 548.286 (±5 mDa), (e) m/z 562.302 (±5 mDa), and (f) m/z 576.318 (±5 mDa) on an ergot body from rye, showing the spatial distribution of the [M+H]+ ions of the ergot alkaloids ergine+erginine, ergometrine+ergometrinine, an untargeted alkaloid, ergosine+ergosinine, ergocornine+ergocorninine, and ergocryptine+ergocryptinine, respectively. (g) and (h) 3D profiling of ergometrine+ergometrinine and the untargeted ergoval, represented by a stack of 2D ion maps of m/z 326.186 (±5 mDa) and m/z 368.195 (±5 mDa); for details see text. The x–y center-to-center distance was 0.3 mm. For other conditions, see Fig. 1
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Fig3: Positive-ion LAESI-TOF-MSI accurate ion maps of (a) m/z 268.142 (±5 mDa), (b) m/z 326.186 (±5 mDa), (c) m/z 368.195 (±5 mDa), (d) m/z 548.286 (±5 mDa), (e) m/z 562.302 (±5 mDa), and (f) m/z 576.318 (±5 mDa) on an ergot body from rye, showing the spatial distribution of the [M+H]+ ions of the ergot alkaloids ergine+erginine, ergometrine+ergometrinine, an untargeted alkaloid, ergosine+ergosinine, ergocornine+ergocorninine, and ergocryptine+ergocryptinine, respectively. (g) and (h) 3D profiling of ergometrine+ergometrinine and the untargeted ergoval, represented by a stack of 2D ion maps of m/z 326.186 (±5 mDa) and m/z 368.195 (±5 mDa); for details see text. The x–y center-to-center distance was 0.3 mm. For other conditions, see Fig. 1

Mentions: A Protea Biosciences (Morgantown, WV, USA) model DP-1000 LAESI system was coupled to a Waters (Manchester, UK) model Synapt G2S mass spectrometer equipped with tri-wave ion-guide optics to optionally separate ions according to their ionic mobility in the gas phase. The LAESI system (Electronic Supplementary Material Figure S1) was equipped with a 2,940 nm mid-IR laser yielding a spot size of 200 μm; unless indicated otherwise, the laser was firing ten times per x–y location at 10 Hz and 100 % output energy. The system was also equipped with a syringe pump delivering a mixture of methanol–water–formic acid (50:50:0.1) at 1 μL min−1, a New Objective (Woburn, MA, USA) model PicoTip 5 cm × 100 μm ID stainless-steel nanospray emitter operated in the positive-ion mode at 3,800 V, and a Peltier-cooled motorized x–y–z sample stage (at 25 or 4 °C) scanned in serpentine mode. The sampling location x–y center-to-center distance was adjusted depending on the specific application needs. The focusing lens L-value and the sample stage Z-value were tuned for each sample with the help of the in-line camera and were typically in the order of 1.9–5.4 and 20.1–21.5 mm, respectively. The LAESI was operated using LAESI Desktop Software v.2.0.1.3 (Protea Biosciences). The TOF mass analyzer of the Synapt G2S was operated in the V-reflectron mode at a mass resolution of 18,000–20,000 (FWHM). The source temperature was 150 °C and the sampling cone voltage was 30 V (20 V in Fig. 3). The mass range acquired was m/z 100–1200 or m/z 100–1500. In QTOF-MS–MS mode the precursor-ion resolution was unity, the collision gas argon, and the trap collision energy 20 eV. In traveling-wave ion mobility (TWIM) TOF-MS mode, the ion-mobility-cell nitrogen gas flow was 90 mL min−1, the wave height 40 V, and the wave velocity 1,000 to 500 m s−1. Synapt MS and TWIM data were processed using MassLynx v4.1 SCN 883 and DriftScope v2.4 software packages, both from Waters. TOF-MS data were lock-mass corrected during data acquisition using the [(C2H6SiO)6 + H]+ impurity ion at m/z 445.1206, which was present in the nanospray background. Ions of potential interest for the generation of accurate mass ion maps were discovered via background subtraction of adjacent base-peak ion (BPI) chronogram regions from those BPI regions that coincided with the analog signal from the mid-IR laser pulses. Ion maps were created in Protea Plot v.2.0.1.3 (Protea Biosciences) after importing of MassLynx raw data files.


Macroscopic and microscopic spatially-resolved analysis of food contaminants and constituents using laser-ablation electrospray ionization mass spectrometry imaging.

Nielen MW, van Beek TA - Anal Bioanal Chem (2014)

Positive-ion LAESI-TOF-MSI accurate ion maps of (a) m/z 268.142 (±5 mDa), (b) m/z 326.186 (±5 mDa), (c) m/z 368.195 (±5 mDa), (d) m/z 548.286 (±5 mDa), (e) m/z 562.302 (±5 mDa), and (f) m/z 576.318 (±5 mDa) on an ergot body from rye, showing the spatial distribution of the [M+H]+ ions of the ergot alkaloids ergine+erginine, ergometrine+ergometrinine, an untargeted alkaloid, ergosine+ergosinine, ergocornine+ergocorninine, and ergocryptine+ergocryptinine, respectively. (g) and (h) 3D profiling of ergometrine+ergometrinine and the untargeted ergoval, represented by a stack of 2D ion maps of m/z 326.186 (±5 mDa) and m/z 368.195 (±5 mDa); for details see text. The x–y center-to-center distance was 0.3 mm. For other conditions, see Fig. 1
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4196196&req=5

Fig3: Positive-ion LAESI-TOF-MSI accurate ion maps of (a) m/z 268.142 (±5 mDa), (b) m/z 326.186 (±5 mDa), (c) m/z 368.195 (±5 mDa), (d) m/z 548.286 (±5 mDa), (e) m/z 562.302 (±5 mDa), and (f) m/z 576.318 (±5 mDa) on an ergot body from rye, showing the spatial distribution of the [M+H]+ ions of the ergot alkaloids ergine+erginine, ergometrine+ergometrinine, an untargeted alkaloid, ergosine+ergosinine, ergocornine+ergocorninine, and ergocryptine+ergocryptinine, respectively. (g) and (h) 3D profiling of ergometrine+ergometrinine and the untargeted ergoval, represented by a stack of 2D ion maps of m/z 326.186 (±5 mDa) and m/z 368.195 (±5 mDa); for details see text. The x–y center-to-center distance was 0.3 mm. For other conditions, see Fig. 1
Mentions: A Protea Biosciences (Morgantown, WV, USA) model DP-1000 LAESI system was coupled to a Waters (Manchester, UK) model Synapt G2S mass spectrometer equipped with tri-wave ion-guide optics to optionally separate ions according to their ionic mobility in the gas phase. The LAESI system (Electronic Supplementary Material Figure S1) was equipped with a 2,940 nm mid-IR laser yielding a spot size of 200 μm; unless indicated otherwise, the laser was firing ten times per x–y location at 10 Hz and 100 % output energy. The system was also equipped with a syringe pump delivering a mixture of methanol–water–formic acid (50:50:0.1) at 1 μL min−1, a New Objective (Woburn, MA, USA) model PicoTip 5 cm × 100 μm ID stainless-steel nanospray emitter operated in the positive-ion mode at 3,800 V, and a Peltier-cooled motorized x–y–z sample stage (at 25 or 4 °C) scanned in serpentine mode. The sampling location x–y center-to-center distance was adjusted depending on the specific application needs. The focusing lens L-value and the sample stage Z-value were tuned for each sample with the help of the in-line camera and were typically in the order of 1.9–5.4 and 20.1–21.5 mm, respectively. The LAESI was operated using LAESI Desktop Software v.2.0.1.3 (Protea Biosciences). The TOF mass analyzer of the Synapt G2S was operated in the V-reflectron mode at a mass resolution of 18,000–20,000 (FWHM). The source temperature was 150 °C and the sampling cone voltage was 30 V (20 V in Fig. 3). The mass range acquired was m/z 100–1200 or m/z 100–1500. In QTOF-MS–MS mode the precursor-ion resolution was unity, the collision gas argon, and the trap collision energy 20 eV. In traveling-wave ion mobility (TWIM) TOF-MS mode, the ion-mobility-cell nitrogen gas flow was 90 mL min−1, the wave height 40 V, and the wave velocity 1,000 to 500 m s−1. Synapt MS and TWIM data were processed using MassLynx v4.1 SCN 883 and DriftScope v2.4 software packages, both from Waters. TOF-MS data were lock-mass corrected during data acquisition using the [(C2H6SiO)6 + H]+ impurity ion at m/z 445.1206, which was present in the nanospray background. Ions of potential interest for the generation of accurate mass ion maps were discovered via background subtraction of adjacent base-peak ion (BPI) chronogram regions from those BPI regions that coincided with the analog signal from the mid-IR laser pulses. Ion maps were created in Protea Plot v.2.0.1.3 (Protea Biosciences) after importing of MassLynx raw data files.

Bottom Line: However, according to three-dimensional LAESI-MSI the penetration depth of imazalil into the peel has significant local variation.Ion maps of different plant alkaloids on ergot bodies from rye reveal co-localization in accordance with expectations.It is envisaged that LAESI-MSI will contribute to future research in food science, agriforensics, and plant metabolomics.

View Article: PubMed Central - PubMed

Affiliation: RIKILT Wageningen UR, P.O. Box 230, 6700 AE, Wageningen, The Netherlands, michel.nielen@wur.nl.

ABSTRACT
Laser-ablation electrospray ionization (LAESI) mass spectrometry imaging (MSI) does not require very flat surfaces, high-precision sample preparation, or the addition of matrix. Because of these features, LAESI-MSI may be the method of choice for spatially-resolved food analysis. In this work, LAESI time-of-flight MSI was investigated for macroscopic and microscopic imaging of pesticides, mycotoxins, and plant metabolites on rose leaves, orange and lemon fruit, ergot bodies, cherry tomatoes, and maize kernels. Accurate mass ion-map data were acquired at sampling locations with an x-y center-to-center distance of 0.2-1.0 mm and were superimposed onto co-registered optical images. The spatially-resolved ion maps of pesticides on rose leaves suggest co-application of registered and banned pesticides. Ion maps of the fungicide imazalil reveal that this compound is only localized on the peel of citrus fruit. However, according to three-dimensional LAESI-MSI the penetration depth of imazalil into the peel has significant local variation. Ion maps of different plant alkaloids on ergot bodies from rye reveal co-localization in accordance with expectations. The feasibility of using untargeted MSI for food analysis was revealed by ion maps of plant metabolites in cherry tomatoes and maize-kernel slices. For tomatoes, traveling-wave ion mobility (TWIM) was used to discriminate between different lycoperoside glycoalkaloid isomers; for maize quadrupole time-of-flight tandem mass spectrometry (MS-MS) was successfully used to elucidate the structure of a localized unknown. It is envisaged that LAESI-MSI will contribute to future research in food science, agriforensics, and plant metabolomics.

Show MeSH