# Commercially Available Blue Diode Laser Engraver Operating at 455 nm as an Affordable LD-REIMS Ionization Source

## TL;DR

A 455 nm blue laser engraver is shown to be a cost-effective ionization source for lipid analysis in salmon tissue, comparable to traditional methods.

## Contribution

Demonstrates a commercially available blue diode laser as an affordable alternative to traditional REIMS ionization sources.

## Key findings

- Optimal laser settings for fresh salmon tissue analysis were 300 mm/min speed and 30–50% power.
- Spectral profiles from the blue laser were similar to those from conventional REIMS methods.
- The visible laser system can distinguish between conventional and organic farmed salmon samples.

## Abstract

Lasers are commonly used for mass spectrometric applications
to
perform laser ablation–desorption and ionization; however,
the use of visible light is not very common. Here, we report a commercially
available visible light laser engraver operating at 455 nm as an ionization
source, generating rich spectral profiles featuring predominantly
lipid species, such as fatty acids and glycerophospholipids. Laser
settings such as the speed of movement over the sample and laser power
were tested, resulting in an optimum laser speed of 300 mm/min and
a laser power of 30–50% for the analysis of fresh salmon tissue
samples. Spectra generated were found to be similar to those produced
by a conventional REIMS mechanism using Joule heating of the tissues,
which was consolidated by comparative studies of the ion formation
mechanism. The generated spectra show a slightly higher signal in
the lower mass range, suggesting a higher degree of in-source fragmentation;
however, no spectral feature was unique to either method. To test
the suitability of the visible laser system to act as an REIMS-like
profiling technique for food authenticity testing, we assessed the
discrimination of Norwegian farmed salmon samples (n = 26) produced using conventional and organic farming methods.