Matías Calcerrada

Analysis of questioned documents: a review.

During the last years (2000-2014), many publications concerning the forensic analysis of questioned documents have been published, and new techniques and methodologies are nowadays employed to overcome forensic caseworks. This article reviews a comprehensive collection of the works focused on this issue, including dating studies, the analysis of inks from pens and printers, the analysis of paper, the analysis of other samples related to questioned documents and studies on intersecting lines. These sections highlight the most relevant analytical studies by a wide range of analytical techniques. Separation and spectrometric techniques are critically discussed and compared, emphasizing the advantages and disadvantages of each one. Finally, concluding remarks on the research published are included.

Forensic discrimination of blue ballpoint pens on documents by laser ablation inductively coupled plasma mass spectrometry and multivariate analysis.

The differentiation of blue ballpoint pen inks written on documents through an LA-ICP-MS methodology is proposed. Small common office paper portions containing ink strokes from 21 blue pens of known origin were cut and measured without any sample preparation. In a first step, Mg, Ca and Sr were proposed as internal standards (ISs) and used in order to normalize elemental intensities and subtract background signals from the paper. Then, specific criteria were designed and employed to identify target elements (Li, V, Mn, Co, Ni, Cu, Zn, Zr, Sn, W and Pb) which resulted independent of the IS chosen in a 98% of the cases and allowed a qualitative clustering of the samples. In a second step, an elemental-related ratio (ink ratio) based on the targets previously identified was used to obtain mass independent intensities and perform pairwise comparisons by means of multivariate statistical analyses (MANOVA, Tukeys HSD and T2 Hotelling). This treatment improved the discrimination power (DP) and provided objective results, achieving a complete differentiation among different brands and a partial differentiation within pen inks from the same brands. The designed data treatment, together with the use of multivariate statistical tools, represents an easy and useful tool for differentiating among blue ballpoint pen inks, with hardly sample destruction and without the need for methodological calibrations, being its use potentially advantageous from a forensic-practice standpoint. To test the procedure, it was applied to analyze real handwritten questioned contracts, previously studied by the Department of Forensic Document Exams of the Criminalistics Service of Civil Guard (Spain). The results showed that all questioned ink entries were clustered in the same group, being those different from the remaining ink on the document.

Fundamentals on new capillaries inspired by photonic crystal fibers as optofluidic separation systems in CE

Two prototypes of microstructured capillaries (MSCs) were designed, manufactured, and used to carry out different experiments. MSC‐1 consisted of six holes of ≈28 μm id whereas MSC‐2 consisted of 85 holes of ≈7.7 μm id. A fundamental study on the hydrodynamic injection through a commercial CE equipment was conducted. Experimental times to flush specific volumes were approximately three times larger than the theoretical values. Then, the detection of starch was carried out by using the MSCs and conventional capillaries, and the electropherograms were compared on the basis of analytical parameters employed in CE. An improvement in peak asymmetry was obtained for the MSC‐1 compared to the conventional capillaries. S/N was one order of magnitude increased with the MSC, improving ten times the sensitivity. Considering this advantage, the separation and detection of nitrostarch was performed as a first application of the MSC‐1. Minimal sample amounts of nitrostarch (1.7 μg) were detected. Results present a real interest in forensics since this substance had not been previously detected through CE, leading to new investigations in the design of new capillaries capable of enhancing CE performance.

A microdestructive capillary electrophoresis method for the analysis of blue-pen-ink strokes on office paper.

This manuscript describes the development of a capillary electrophoresis (CE) method for the detection of acid and basic dyes and its application to real samples, blue-pen-ink strokes on office paper. First, a capillary zone electrophoresis (CZE) method was developed for the separation of basic and acid dyes, by studying the separation medium (buffer nature, pH and relative amount of additive) and instrumental parameters (temperature, voltage and capillary dimensions). The method performance was evaluated in terms of selectivity, resolution (above 5 and 2 for acid dyes and basic dyes, respectively, except for two basic dye standards), LOD (lower than 0.4 mg/L) and precision as intraday and interday RSD values of peak migration times (lower than 0.6%). The developed method was then applied to 34 blue pens from different technologies (rollerball, ballpoint, markers) and with different ink composition (gel, water-based, oil-based). A microdestructive sample treatment using a scalpel to scratch 0.3mg of ink stroke was performed. The entire electropherogram profile allowed the visual discrimination between different types of ink and brands, being not necessary a statistical treatment. A 100% of discrimination was achieved between pen technologies, brands, and models, although non-reproducible zones in the electropherograms were found for blue gel pen samples. The two different batches of blue oil-based pens were also differentiated. Thus, this method provides a simple, microdestructive, and rapid analysis of different blue pen technologies which may complement the current analysis of questioned documents performed by forensic laboratories.

Validation of an analytical method for the refractive index measurement of glass fragments. Application to a hit-and-run incident

A method to determine the refractive index (RI) of glass samples was validated in this research article. This validation was performed by studying analytical features such as the working range, precision, robustness, and bias. Locke silicone oil type B, glass standards type B and a sodium D source (589.3 nm) were chosen for a working RI range from 1.50225 to 1.52381, according to the typical RI values of glass samples of forensic interest. Robustness, calculated as Relative Standard Deviation (RSD) of slopes of ten calibration lines within a period of one month was 0.24%. Precision of the method (calculated for the two extreme glass standards B2 and B12 in the working range) was 0.21% and 0.14% (repeatability) and 0.12% and 0.09% (intermediate precision), respectively. A Certified Reference Material (CRM) of glass of known RI was employed to estimate the bias of the method, verifying a relative error of 0.00066%. The method was applied to eight validation samples (six glass fragments from different parts of an automobile, a glass container and an architectural tinted window), which were differentiated through their RI values. Finally, the procedure was applied to interpret the origin of glass evidence taken from a hit-and-run incident. A common origin of recovered and control glass fragments was supposed on the basis of the RI determination of these samples, together with the application of useful match criteria in forensic pairwise comparisons of glass fragments. Results were confirmed by means of a highly discriminatory technique such as Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS).

Monitoring of the stability of cocaine and some metabolites in water and oral fluid by a newly developed CE method

A new CE method was here developed, in order to study the stability of cocaine and some of its metabolites in water and in oral fluid. At first, standard mixtures of cocaine (COC), benzoylecgonine (BE) and cocaethylene (COET) in water were used to study the optimal CE parameters to separate the three compounds. Voltage, sample temperature and pH were investigated, and 25 kV, 25°C and a pH of 4.7 were selected to achieve the best separation. The stability of the three compounds in water and oral fluid was then monitored by applying the previously developed method. Three different storage temperatures (8, 25 and 37°C) were selected and analyses during a week were performed. A decrease of COC and COET peak areas and an increase of BE peak area were observed over time at 25 and 37°C. In addition, in oral fluid, the presence of enzymes and other proteins, and the differences in the molecular structures between COC and COET, caused a stronger degradation of the first compound. Instead, when samples were stored at a low temperature (8°C), the peak areas of the compounds did not vary. Thus, the use of this storage temperature is recommended, above all when sample must be analyzed after a relatively long time.

Measuring the Human Ultra-Weak Photon Emission Distribution Using an Electron-Multiplying, Charge-Coupled Device as a Sensor

Ultra-weak photon emission (UPE) is the spontaneous emission from living systems mainly attributed to oxidation reactions, in which reactive oxygen species (ROS) may play a major role. Given the capability of the next-generation electron-multiplying CCD (EMCCD) sensors and the easy use of liquid crystal tunable filters (LCTF), the aim of this work was to explore the potential of a simple UPE spectrometer to measure the UPE from a human hand. Thus, an easy setup was configured based on a dark box for inserting the subject’s hand prior to LCTF as a monochromator and an EMCCD sensor working in the full vertical binning mode (FVB) as a spectra detector. Under controlled conditions, both dark signals and left hand UPE were acquired by registering the UPE intensity at different selected wavelengths (400, 450, 500, 550, 600, 650, and 700 nm) during a period of 10 min each. Then, spurious signals were filtered out by ignoring the pixels whose values were clearly outside of the Gaussian distribution, and the dark signal was subtracted from the subject hand signal. The stepped spectrum with a peak of approximately 880 photons at 500 nm had a shape that agreed somewhat with previous reports, and agrees with previous UPE research that reported UPE from 420 to 570 nm, or 260 to 800 nm, with a range from 1 to 1000 photons s−1 cm−2. Obtaining the spectral distribution instead of the total intensity of the UPE represents a step forward in this field, as it may provide extra information about a subject’s personal states and relationship with ROS. A new generation of CCD sensors with lower dark signals, and spectrographs with a more uniform spectral transmittance, will open up new possibilities for configuring measuring systems in portable formats.

Optimized photonic crystal fibers supporting efficient capillary electrophoresis

In this paper we present preliminary results on the use of Photonic Crystal Fibers (PCFs) in a conventional capillary electrophoresis system to separate and detect fluorescent species. PCFs show interesting advantages over conventional capillaries for this application, including larger surface-to-volume ratio and potential for higher resolution with comparable sensitivity. Our results illustrate some of these advantages, and we point out the need for stringent tolerances in the fabrication of specific PCFs for this application.