Forgeries foiled: EASI mass spectrometry identifies falsified vehicle registration documents

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Counterfeiting of legal documents, identity cards, passports and banknotes is an increasing problem worldwide, with an array of measures adopted by the forgers to try and dodge detection. The problem is seen to be particularly acute in Brazil, where a large number of counterfeiting methods have been adopted by the criminal fraternity.

The growing skill of forgers has led to the introduction of devices such as holographs, magnetic strips and watermarks to make it more difficult to produce convincing counterfeits. Inspection of suspect documents usually begins with visual examination, backed up by optical evaluation of image quality and finally by chemical and spectroscopic procedures. Many of these involve mass spectrometry in its various forms but a novel method has been introduced by a team of Brazilian researchers.

With senior reporter Wanderson Romao from UNICAMP (Universidade Estadual de Campinas), the team included Marcos Eberlin who has just been appointed associate editor of the Journal of Mass Spectrometry, as well as scientists from the Criminalistic Institute Dr. Octavio Eduardo de Brito Alvarenga, Sao Paulo, and the Federal University of Espirito Santo, Vitoria.

They turned to one of the recently developed ambient mass spectrometry procedures involving easy ambient sonic spray ionisation (EASI) for the detection of falsified vehicle registration documents.

Sonic boom in counterfeit detection

EASI MS was developed by Eberlin in 2006 and has the distinct advantage over other ionisation techniques that the source can be constructed within a few minutes from common lab components. It has been described as one of the easier ambient mass spectrometric techniques to implement because it does not require an electrical discharge or heating.

A sonic spray containing charged particles is produced when a liquid is sprayed with a coaxial flow of supersonic gas. The charged particles are directed towards the sample surface at which they induce desorption and ionisation of the compounds in the target area. The spray tip is typically positioned a few mm from the target surface and the mass spectrometer inlet is approximately the same distance at an angle to draw in the ions.

In this case, methanol containing aqueous acetic acid or aqueous ammonium hydroxide was used as the spray solution for positive- and negative-ion mode, respectively.

A set of 40 authentic and questionable vehicle registration documents was analysed without any sample pre-treatment. The EASI source was connected to a single quadrupole mass spectrometer and significant peaks in the spectra were identified by linking the source to an FT/ICR mass spectrometer operating in MS/MS mode.

The spectra from the authentic and known counterfeit documents were compared to see if there were any features that distinguished the two types.

Forged document discovery made EASI

Mass spectra taken from three positions on the authentic documents gave very similar chemical profiles, indicating that the spray position on this type of target was not a factor to consider. In negative-ion mode, no compounds were detected but the positive-ion spectra revealed the presence of several components.

The ions at m/z 391, 413 and 429 were attributed to the protonated, sodiated and potassiated forms of the plasticiser bis(2-ethylhexyl) phthalate, the structure being confirmed by MS/MS.

The biocide dihexadecyldimethylammonium was also detected in positive-ion mode, with a protonated molecule at m/z 494.

The positive-ion spectra of the counterfeit documents were very similar to those of the authentic samples, with no conspicuous features to aid discrimination. However, the negative-ion spectra contained a strong ion at m/z 249 which was absent from the authentic documents.

This ion was assigned to 4-(octyloxy)benzoic acid, which is often added to printer inks as a stabiliser. By inference, it is not used by official documentation centres to produce vehicle documents and provides a means to identify the counterfeit versions.

The researchers printed a sheet of paper from three different printers in the lab to see if they could link the forged documents to a particular printer. Only the spectrum from a Laserjet printer contained the negative ion from the stabiliser, which was absent from the spectra of documents printed with Phaser and Deskjet printers.

So, a Laserjet printer might have been used to make the forgeries, although this conclusion cannot be supported without a full study of the printing inks of a wide range of printers.

Nonetheless, the presence of a peak at m/z 249 in the negative-ion EASI mass spectra of a vehicle document issued in Brazil is a strong indication of a forgery. EASI MS offers a simple and rapid non-destructive method for examining suspect vehicle registration documents.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.