Dating the writing age of black roller

Forensic Science International 162 (2006) 140–143 www.elsevier.com/locate/forsciint

Dating the writing age of black roller and gel inks by gas chromatography and UV–vis spectrophotometer Yuanyuan Xu a,*, Jinghan Wang b, Lijuan Yao b a

Guangdong Police College, Department of Investigation, 500 Binjiangdong Street, Guangzhou, Guangdong 510232, PR China b China Criminal Police College, Department of Forensic Medicine, P.O. Box 755, 83 Tawan Street, Shenyang, Liaoning 110035, PR China Available online 18 July 2006

Abstract The relative and absolute age of roller and gel ink entries determined by gas chromatography (GC) and UV–vis methods are presented in this paper. The relative age of ink entries is concluded by the comparison of solvent amount between questioned and known dated entries. Absolute age of ink entries is estimated through the changing ratio of solvent components between heated and unheated samples without known samples for comparison. The methods are accurate and reliable. # 2006 Elsevier Ireland Ltd. All rights reserved.

Keywords: Roller inks; Gel inks; Relative age; Absolute age; Dating; Gas chromatography; UV–vis spectrophotometer

The analysis of roller pen and gel inks is more and more necessary with the extensive use of roller and gel pens in fraudulent documents. So dating the writing age of roller and gel ink is very important for forensic scientists. At present classes tested is in progress by using optical and chemical techniques, such as Raman spectroscopy, microspectrophotometry [1], GC/MS [2–5] and HPCE [6], but dating the writing age of black roller pen and gel inks have not been reported.

So some forensic scientists pay attention to the approaches determining the dynamic characteristics of roller pen ink age.

When the samples known writing age compared with the questioned ink are usable, relative writing age is estimated by using GC and UV–vis. When known samples are not been had, absolute writing age is estimated through solvent changing ratio between heated and unheated samples. The six black roller and gel inks are identified by qualitative and quantitative analysis of the solvent components and dye components using the methods of GC and UV–vis.

* Corresponding author.

E-mail address: xyy0123@163.com (Y. Xu).

0379-0738/$ – see front matter # 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.forsciint.2006.06.011

1. The relative writing age of black roller pen inks 1.1. Experiment 1.1.1. Materials and methods 1.1.1.1. Samples. The experimental inks are listed in Table 1.

Lines of the six black roller pen and gel inks have been written on white papers for notes put into a drawer.

1.1.1.2. Instruments. A Hewlett-Packand Model 6890 gas chromatography equipped with a flame ionization detector (FID); A Shimadzu Model 250 UV-VIS Spectrophotometer.

GC Condition: column: DB-FFAP, 30 m 320 mm ID 0.25 mm; carrier: nitrogen, 2.5 mL/min; oven program: 60 8C (1 min) 10 8C/min 135 8C 15 8C/min 220 8C (4 min); injection: 2 mL, splitless, T = 240 8C; detector: FID, T = 280 8C, hydrogen, 35 mL/min, air; 350 mL/min.

1.1.1.3. Procedure 1. A 2 cm in length samples of entries written are cut out with a sharp scalpel and analyzed by using GC and UV–vis methods as follows.

Every sample is extracted in a vial with 1 mL methanol containing ethyl benzoate (ethyl benzoate is used as external comparative matter) for 20 min to maximize the amount of all

Y. Xu et al. / Forensic Science International 162 (2006) 140–143 Table 1 Samples of experimental inks Number

Brand

Manufacturer

1 2 3 4 5 6

ZEBRA Be-pen (R-100) ZEBRA Be-pen (Be-109) SCHENIDER TOP BALL 861 03 STAEDTLER NORIS Pen 333 Rollerball refill MONT BLANC SCHENIDER TOP LINER 967

Japan Japan Germany Germany Germany Germany

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available volatile components of ink. After extraction, 2 mL of every sample is removed and analyzed by GC. The residual solution of extraction is extracted secondarily with 0.9 mL DMF for 20 min to maximize the amount of all available dye components of ink. The solvent of extraction is analyzed by UV–vis and the absorption spectra of the colored extracts obtained are recorded. The absorbance measured at the absorption maximum of a dye presented in the ink analyzed is read for every sample.

The aging parameters can be ascertained: the Ratio is determined by the peak area of solvent to the peak area of external comparative matter to the absorbance of dye: ratio ¼

peak area ðsolventÞ ½peak area of external comparative matter peak area ðdyeÞ

(1)

Then aging curve (see Fig. 1) for known writing age of ink can be obtained from these ratios plotted versus actual age.

Throughout the aging curves, the writing age of the questioned entries can be evaluated from the ratio.

2. Results and discussions

Fig. 1. Natural aging curve of the Ratio of known dated samples decreasing with the time.

If the ink sampling has at least two solvent components, two or more aging curves can be obtained. Then the writing aging of the questioned entries can be evaluated from more ratios and it is more accurate. The results can be verified one another.

Fig. 2 shows that two chromatographic peak areas of solvent components in no. 5 decrease with the time. Because the solvent components have special volatility, the contents decrease with the time.

The content of external comparative matter is almost unvarying. The physical and chemical reactions of dye components in the ink nearly do not happen in initial 3 months, so the ratios decrease.

The roller and gel inks are complex mixtures. They are composed of solvents (volatile components), dyes, synthetic resins and other organic compounds that begin changing or evaporating as soon as the ink is placed on a paper. The rates of these processes are significantly different. The evaporation of the solvent components is very intensive initially and it

Fig. 2. Graphical presentation of two chromatographic peak areas of no. 5 decreasing with the time.

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Y. Xu et al. / Forensic Science International 162 (2006) 140–143

Ratio (questioned) > ratio (known): the age of questioned entries is older than the age of known entries.

3. The absolute writing age of black roller and gel inks 3.1. Experimental 3.1.1. Materials and methods The samples and instruments are as above.

3.1.1.1. Procedure 2. The known entries are heated at 60 8C in an oven for 1 h. A 95 8C is compared, but the ratio does not change any longer an hour later. That will lead to more determinate errors.

The solvent and dye components of the unheated and heated ink entries are detected as it is described in Section 1.1.1.3.

Analytical results of no. 5 are showed in Fig. 3. The value of D (%) represented the changing ratio between unheated and heated is calculated: Fig. 3. Graphical presentation of R (ratio of unheated entry) and RT (ratio heated entry) of no. 5.

decreases quickly in the first hour and day after roller and gel ink have been written on a paper. The oxidation, crossinglinking and other similar processes go more slowly, so much as never happen, because the samples are not exposed to light or heated. The evaporation rates of the solvents components are influenced by many factors, such as the thickness of ink line (depth of the film of the writing), environment, formula of ink and nature of component, and so on. The absorbance of a dye is measured in order to eliminate the influence of the thickness of ink line. The appropriable external comparative matter is selected and analyzed with the solvent components together by GC, so it can do its best to eliminate the error of instrument. The formula of ink, the preservative conditions of the known entries must be same as the questioned entries.

The ratio of questioned entries comparing with the ratio of known dated entries, there will appear three situations: Ratio (questioned) < ratio (known): the age of questioned entries are younger than the age of known entries.

Ratio (questioned) = ratio (known): the age of questioned entries is the same as the age of known entries.

D ð%Þ ¼

R RT R

100%

(2)

R is the value of unheated entry, RT is the value of heated entry.

The curve of D% as time is showed in Fig. 4. The questioned entries are analyzed and detected as described in Section 1.1.1.3, then calculated by Eq. (2). The scope of writing age of the questioned ink entries is confirmed.

4. Results and discussions The relative aging approach requires that the inks being compared should be on the same paper and be of the same formula, but many situations do not meet these requirements. In order to solve these problems, heat accelerated aging approach is used. The method requires neither a questioned ink formula identification nor known inks for comparison.

It is found that the ratio of unheated entries is larger than the ratio of heated entries in the initial 90 days, and in the progress the distance of values between unheated entries and heated entries is gradually smaller. But the value of the heated entries is almost as the same as the unheated entries after 90 days in Fig. 3. The reason is the evaporation of the solvent components goes fast initially and then more slowly.

Fig. 4. Aging curve of absolute writing age that D% decreasing with the time.

Y. Xu et al. / Forensic Science International 162 (2006) 140–143

To summarize above, the following three typical situations are considered that can take place depending on the magnitude of D% value obtained for the questioned ink, on condition that the ink entries have been stored under normal environmental conditions as room temperature and not exposed in light: 30% D% 80%: it shows that the questioned entries are fresh. The writing age is less than ten days.

0% < D% < 30%: it shows that the writing age is between 10 and 90 days. If the value is very nearer to 0% or 30%, more samples should be taken and more experiments should be carried out to calculate the statistical mean value.

D% = 0: it shows that the questioned entries are old. The writing age is more than 90 days. More experiments also should be carried out to ascertain statistically to avoid the artificial error and determinate error.

5. Conclusions The technique having been described based on using GC and UV–vis can be applied effectively for determining the relative age and absolute age of roller and gel ink entries. It is a very important method that absolute age is determined by D% value,

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because known writing age entries for comparison need not be required. The method can be solved many practical problems.

Acknowledgments I am quite thankful to my mentor Jinghan Wang and teacher Yao for giving me so much help and support, and Alma Mater China Criminal Police College for providing with the instruments.

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