Evan Parker; Carlito Lebrilla
UC Davis, Davis, CA
First application of monodisperse polymers for encoding information in materials. Derivative methods could lead to commodity utility of mass spectrometry.
Product safety of pharmaceuticals and food products being of paramount, industry expends great effort in the tracking and validation of product source and identity throughout the supply chain. Here, a method is described that uses a food safe, GRAS status, oligomer marker to encode binary information in bulk materials. Similar methods employ the use of dyes, fluorescent compounds, nanoparticles, microfabricated markers, and macroscopic markers. These methods tend to be either costly or easily replicated while often having the benefit of easy detection. In our method a host of monodisperse formulated polyethylene glycol oligomers can be added to a product to encode binary information detected and can be easily with MALDI MS.
We are using oligomers of polyethylene glycol (PEG) as single-unit characters in our encoding scheme. This category of molecule is useful because it is inert, nontoxic, and synthetic methods exist that would allow preparation at scale. As a proof of concept, eight oligomers of this compound ranging in length from 11 to 19 subunits were fractionated by reversed phase HPLC. The oligomers are then added to test mixtures and detected using MALDI mass spectrometry with DHB matrix. Both MALDI FT-ICR and MALDI-TOF were used to test the method. To find limits of detection we doped dilutions of a polydisperse mixture of PEG 600 into various matrices. Clear detection of the most abundant eight peaks constituted a positive hit.
To prepare peg monomers, reversed phase chromatography was employed to separate mixtures of PEG 600 and PEG 1000 into their monodisperse components. Monitoring the absorption trace at 192 nanometers showed clear baseline separation even in overloading conditions necessary for preparation. Using this method, between 0.5 and 1 mg of each of the purified monodisperse components from 10 to 20 subunits long were collected. These collected markants were doped at approximately 100 ppm into both water and milk as a proof of concept for the actual encoding of information. We used mass spectrometry to collect the codes 11111111, 01001101, and 01010011 encoding to binary 255, and ASCII M and S respectively.
Using serial dilutions of polydisperse peg 600 we show that acceptable signal to noise can be achieved at concentration of 1 ppm by mass. To prove the utility of the markant in complex samples, various concentrations of the polydisperse solution were added to whole milk. We have shown that PEG can be readily detected at 50 ppm with a simple cleanup procedure entailing centrifugation and reversed phase SPE. To confirm the method’s utility as a surface marker, various amounts were sprayed on the surface of a cantaloupe and, after a week of storage on a shelf, PEGs were recovered via an extraction procedure entailing the peeling of the cantaloupe and vortexing of diced peel with water. We showed that the detection limit is below 0.1% spray concentration or 4 mg per 100 square centimeters or, roughly 50 mg for a 20 cm diameter cantaloupe that has been uniformly treated.