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ASMS 2018: MALDI Imaging and Laser Ablation Sampling for Analysis of Fungicide Distribution in Apples

ThOC 8:50

Igor Pereira, Bijay Banstola, Kelin Wang, Boniek Gontijo Vaz, Fabrizio Donnarumma, and Kermit K. Murray

Louisiana State University & Federal University of Goiás

Imazalil is a postharvest fungicide widely used for mold control in apples and has been classified as a potential cancerogenic in the NIH Hazardous Substances Data Bank. Imazalil is applied to apples by dipping, drenching, or spraying using concentrations between 1000 and 2000 ppm. The fungicide can penetrate the exocarp (outer skin) and diffuse into the interior mesocarp region of the fruit. MS analysis of imazalil treated apples is commonly conducted using the entirety of the fruit, which results in loss of localization information and does not provide any information about the rate of penetration. MALDI imaging can provide localization of imazalil and laser ablation can extract the compound with minimal sample prep for subsequent ESI MS.

Infrared laser ablation and capture of enzymes with conserved activity

Wang, K., Donnarumma, F., Baldone, M. D., & Murray, K. K. Infrared laser ablation and capture of enzymes with conserved activity. Anal Chim Acta, 1027, 41–46 (2018).

Abstract

Infrared (IR) laser ablation at 3 μm wavelength was used to extract enzymes from tissue and quantitatively determine their activity. Experiments were conducted with trypsin, which was ablated, captured and then used to digest bovine serum albumin (BSA). BSA digests were evaluated using matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) and sequence coverage of 59% was achieved. Quantification was performed using trypsin and catalase standards and rat brain tissue by fluorescence spectroscopy. Both enzymes were reproducibly transferred with an efficiency of 75 ± 8% at laser fluences between 10 and 30 kJ/m2. Trypsin retained 37 ± 2% of its activity and catalase retained 50 ± 7%. The activity of catalase from tissue was tested using three consecutive 50 μm thick rat brain sections. Two 4 mm2 regions were ablated and captured from the cortex and cerebellum regions. The absolute catalase concentration in the two regions was consistent with previously published data, demonstrating transfer of intact enzymes from tissue.