Lipid analysis of flat-mounted eye tissue by imaging mass spectrometry with identification of contaminants in preservation

Abstract

Matrix-assisted laser desorption/ionization imaging mass spectrometry was used to analyze donor eye tissue specimens for phospholipid content to evaluate lipid distribution. Phosphatidylcholines and sphingomyelins were detected in the positive ion mode using 2,5-dihydroxybenzoic acid as the matrix. During this study, unknown ion signals in the lower m/z region (less than m/z 400) were detected, mainly in the far periphery of human flat-mounted tissue but not in age-matched rhesus monkey tissue prepared in a similar manner. The unknown ion signals occurred at m/z 304, 332, 360, and 388. These ions were subjected to tandem mass spectrometry directly from the tissue sample, and exact mass measurements of extracts were prepared for further identification. These ions were identified as alkyl dimethylbenzylammonium surfactants (benzalkonium chlorides (BACs)). The classification of these species was verified by comparing an eye tissue extract to an over-the-counter eye-care product containing BACs.

Spatially resolved analysis of small molecules by matrix‐assisted laser desorption/ionization mass spectrometric imaging (MALDI‐MSI)

“…Metabolite distributions in barley grains appear at the tissue level rather than at the single‐cell level, and cellularization levels vary strongly from very young grains (1–6 DAP) to grains in the seed filling or mature stage (7–20 DAP). Some tissues require a higher resolution measurement than others – for example, the aleurone layer is only two to three cell layers thick (Garrett et al. , 2011).…”

“…These phospholipid classes are expected to produce fragment ions of m/z 104 and 184 and a neutral loss of m/z 59 (Xu et al. , 2009; Garrett et al. , 2011; Murphy & Gaskell, 2011).…”

“…Ó 2011 The Authors New Phytologist Ó 2011 New Phytologist Trust cell layers thick (Garrett et al, 2011). As a result, the resolution adopted for 1-6-DAP grains was 10-20 lm and, for 7-20-DAP grains, 20-35 lm (for details, see Table S1).…”

The potential of mass spectrometry imaging in plant metabolomics: a review

“…This study (Garrett et al 2011) also addressed concerns from sceptics with regards to reproducibility of MALDI-MSI analyses. Reproducibility was verified both through biological replicates but also using both longitudinal and cross-sections.…”

“…With this said, some tissue types are composed only of a few cell layers and thus would require higher resolution measurements (close to single-cell level). A good example of such a specific tissue type is the aleurone layer around the endosperm in seeds which normally is only two or three cell layers thick (Garrett et al 2011).…”