Photofading of ballpoint dyes studied on paper by LDI and MALDI MS

Abstract

The determination of the age of an ink entry from a questioned document is often a major problem and a controversial issue in forensic sciences. Therefore, it is important to understand the aging process of the different components found in ink. The aim of this work is to characterize the degradation processes of methyl violet and ethyl violet, two typical ballpoint dyes by using laser desorption/ionization (LDI) and matrix-assisted laser desorption/ ionization (MALDI) mass spectrometry (MS), and to evaluate the possible application of the method to forensic examination of documents. The mass spectrometric methods were first tested and were found to be adequate for the purpose of this work. Moreover, it is possible to analyze the dye from a stroke directly from the paper (LDI-MS), so the sample preparation is minimized. The degradation of the dyes methyl violet and ethyl violet in strokes from a ballpoint pen was studied under laboratory conditions influenced by different factors such as light, wavelength of light, heat, and humidity. Then, strokes from the same ballpoint were aged naturally in the dark or under the influence of light over one year and then analyzed. The results show that the degradation of these dyes strongly depends on light fluence. Humidity also increases degradation, which can be explained by the basicity of the paper. The influence of heat on the degradation process was found to be rather weak. It was also observed that the dyes from the ink strokes did not show significant degradation after one year of storage in the dark. In conclusion, the storage conditions of a questioned document and the initial composition of the dyes in the ink have to be known for correct interpretation of the age of an ink entry. Measurements over longer periods of time are necessary to follow the degradation of dyes exempt from light exposure. LDI was found adequate and very useful for the analysis of ballpoint dyes directly from paper without further pretreatment. n the field of forensic examination of questioned documents, the legitimacy of an ink entry is often an essential question, and the possibility of determining the age of an ink stroke would definitely help to resolve this problem. Ballpoint pens are very common scriptural instruments, the inks of which contain equivalent amounts of dyes, solvents, and resins. After deposition on paper, the ink composition begins to change qualitatively and quantitatively: the resins polymerize, the solvents evaporate, and the dyes fade. Throughout the years, many different methods were developed to measure the changes occurring in the ink with time [1][2][3][4][5][6][7]: decrease of extractability of ink through hardening of the resins [8 -13, 16], disappearance of solvents [14 -20], and degradation of dyes [18,[21][22][23][24][25][26][27][28][29]. The analysis of the latter compounds involve techniques such as microspectrophotometry [21], HPLC analysis [25,26], or recently mass spectrometry [18, 22-24, 27, 28]. Laser desorption/ionization mass spectrometry (LDI-MS) i...

Química forense: perspectivas sobre novos métodos analíticos aplicados à documentoscopia, balística e drogas de abuso

“…17,19,20 Os primeiros estudos direcionados para a análise de tintas em documentos surgiram no período de 2005-2006. 16,18 Laser desorption ionization mass spectrometry (LDI-MS) e matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) são ferramentas analíticas muito utilizadas na análise de corantes. O uso de MALDI-MS e LDI-MS pode envolver pouca preparação de amostra.…”

“…Ocorre a dessorção e a ionização do analito, sendo os íons formados atraídos para o analisador de massas. 16 Weyermann e colaboradores 16 investigaram o envelhecimento dos corantes violeta de metila (MV) e violeta de etila (EV), usados em canetas esferográficas de coloração azul. Envelhecimentos acelerados (temperatura, luz, e umidade) e naturais (1 ano) foram estudados.…”

“…Os autores afirmam que a degradação natural ocorrida com os documentos antigos são fatores não controláveis, onde cada documento pode ter sido armazenado ou exposto a condições diferentes, sendo necessário, portanto, um grande número de documentos para a realização de uma metodologia de validação analítica. Entretanto, uma estimativa é feita para um documento de 10 anos, onde os cálculos de RPA 372 mostraram corresponder a um envelhecimento acelerado de 6 h. Outro resultado interessante é que a variação do RPA 372 com o tempo apresenta uma relação linear quando se usa uma lâmpada incandescente, diferentemente do trabalho anterior, onde o valor de RPA 372 se estabiliza em 30%, 16 corroborando a importância da elaboração de metodologias de validação analítica onde os valores de RPA 372 obtidos pelos estudos de envelhecimentos acelerados e naturais poderiam ser correlacionados.…”

“…Essa evolução na área de MS se deve principalmente ao surgimento de novos sistemas de ionização, como EASI (easy ambient sonic-spray ionization), DESI (desorption electrospray ionization) e DART (direct analysis in real time). [16][17][18][19][20][21][22][23][24] A partir de 2005, vários trabalhos começaram a ser publicados (13 publicações e 151 citações, respectivamente) sendo, atualmente, a EASI uma das técnicas usadas pela Polícia Federal Brasileira na investigação da autenticidade de documentos questionados.…”

Analysis of writing inks on paper using direct analysis in real time mass spectrometry

“…Both laser desorption mass spectrometry (LDMS) [31][32][33][34][35][36][37] and matrix-assisted laser desorption and ionization (MALDI) mass spectrometry have been studied [35,38]. Secondary ion mass spectrometry (SIMS) has also been tested [39][40][41].…”