FRS581 Laboratory ReportTLC of Pen Ink

Nur Atiqah binti Ahmad2013574299

Date Performed: 11th May 2015Date Submitted: 18th May 2015

Group: AS2534B1

Lecturer: Pn. Khairulmazidah binti Mohamed

Introduction

The ink in modern ball point pens is a mixture of various dyes components blended together to get the desired colour. Each pen manufacturer will have a unique formulation for their inks. In forensic investigation, ink analysis may be an important part of the investigation ofquestioned documents, including forged checks, wills, or altered records. Although all blue or black inks may look the same, there can be some important differences in their chemical composition. These can be revealed by laboratory analysis and the results can help assess whether there have been any additions or alterations to a document.

In todays experiment you will separate the ink pigments using a technique called Thin Layer Chromatography (TLC). TLC works by moving the ink along a strip of plastic coated with a thin layer of alumina or silica gel. The coating on the strip is called the stationary phase. The ink is moved along the stationary phase by a solvent or a mixture of solvents called mobile phase. Each pigment will have unique affinity to the stationary phase as well as a unique solubility in the mobile phase. The greater the affinity to the stationary phase, the slower the pigment travels. The greater the solubility in the mobile phase, the faster the pigment travels.

ObjectiveTo understand and experience ink analysis using Thin-layer chromatography technique

Materials

Pencil Metric ruler Precoated silica chromatography plateSeveral ball-point pens, white paper95% ethanol / pyridineEthyl acetate

Distilled water Capillary tube BeakerAluminium foilVideo Spectral Comparator(VSC)

ProcedureThe mobile phase: The mobile phase solution was prepared using 7.5mL ethyl acetate, 3.5mL 95% ethanol and 3.0mL distilled water to a 100mL screw cap reagent storage bottle. The solution was mixed to make it homogeneous.

Separation technique;1. The mobile phase was added to the beaker to attain a height of 5 mm.2. The beaker was saturated with mobile phase vapors by closing the beaker with aluminum foil and was left stand at least 15 minutes. 3. Words were written on pieces of paper using pen from different brands of similar ink colour. 4. 2 drops of 95% EtOH or pyridine was added on each word written using different pen. The solvent was observed until the ink is dissolving into the liquid. 5. 1cm from the bottom of a short edge of the TLC plate was marked using pencil. 6. 1cm before the end of the TLC plate was marked using pencil as an end line for solvent front.7. A clean capillary tube was used to spot each sample along the first pencil line.8. The location of each sample was noted. 9. The TLC plate was carefully positioned in the beaker and covered with aluminum foil. 10. The progress of the solvent front was checked every 2-3 minutes. 11. The plate was removed from the beaker once the solvent front reach about of the TLC plate length the solvent front was marked pencil. 12. The TLC plate was allowed to dry completely. 13. The TLC plate was photographed to be included in the report. 14. The center of each band was marked. 15. The Rf value for each band was calculated by dividing the distance travelled by the band by the distance travelled by the solvent. 16. Each ink yielded a unique profile by comparing the number of bands and their corresponding Rf values.

Data and Result:

Figure 1: Dye component of ink samples of different brands. (a) view under white light (b) viewed under fluorescence light.

Table 1: Dye component of ink samples of different brandsBrandInk components

Stabilo 5

Paper Mate5

No brand7

Faber Castle 4

Table 2: Distance traveled by dye component of ink samples of different brandsInk componentsDistance travelled, cm

Stabilo Paper MateNo brandFaber Castle

14.654.654.654.50

24.954.954.904.85

35.195.155.105.10

4--5.20-

5--5.35-

65.705.605.60-

76.306.256.206.20

Table 3: The retention factor Rf of the dye component of pen ink samplesInk componentsRetention factor, Rf*

Stabilo Paper MateNo brandFaber Castle

10.6690.6690.6690.647

20.7120.7120.7050.698

30.7470.7410.7340.734

4--0.748-

5--0.770-

60.8210.8060.806-

70.9060.8990.8920.892

*distance travel by solvent front = 6.95cm

Discussion

In this practical, black ink samples from different brand were tested using thin layer chromatography. The ink samples were first dissolved in pyridine for extraction. The ink samples were spotted on the silica plate and placed in a closed beaker in mobile phase. The silica plate then was removed when the solvent reach the end of the plate and dried at room temperature. The silica plate was observed under fluorescence light.

Sometimes inks of similar colour can look identical to the naked eye but further tests may be able to distinguish between them.Most commercial ink is made up of a mixture of several organic dyes. These dyes can be split up on appropriate developed thin layer chromatography plate (Saferstein, 2014). Once a TLC plate was run in the mobile phase, clear bands visible on the plate indicating the separation of different components of the ink were formed as shown in Figure 1. From the experiment, it is shown that black ink from Stabilo, Paper Mate, No brand, and Faber Castle is made up of 5, 5, 7 and 4 different components respectively. The distance travelled by each component from different ink samples was recorded in Table 2 above. The retention factor Rf calculated for each component of different samples was recorded in Table 3 above.

Most ink formulation has similar dyes components and some have different components. This makes a unique characteristic of the ink samples. In forensic analysis, this characteristic is importance when the questioned documents need to be compared to the known document. For example, ink analysis can reveal whether there an addition of number in a forged cheque or not.

Figure 1 shows the silica plate observed under the white light (a) and under the fluorescence light (b). Under white light, the true colour of the component can be distinguished. Under the fluorescence light, all the dye components appear to be the same and not obviously separated. Under the fluorescence light, some component cannot be seen. Based on the Figure 1, the yellow component seen under the white light was not observed under the fluorescence light but component that are hard to be observed with naked eye is brightly seen under the fluorescence light.

ConclusionIn conclusion, dye components of the ink samples can be separated and distinguished using thin layer chromatography technique. This experiment demonstrates that TLC can he used to identify qualitatively an unknown compound provided suitablestandards are available. The procedure insures that each student makes hislher own observations and calculations. Becausethe components in the inks are visible, no special visualization techniques are required. Finally, the experiment is economicalbecause the TLC plates are prepared in our laboratory; we have found that 'Iti-in. douhle-strength window pane worksverywell as the support for the Silica Gel thus eliminating the need to buy commercial plates

Questions1. Apart from TLC, what other methods can be used to differentiate ink?Alterations, obliterations and erasures not visible to the human eye can often be detected through use of photography and other imaging devices that utilize ultraviolet and infrared wavelengths of light. Using radiation filtered at various wavelengths, an imaging instrument such as a video spectral comparator (VSC) can reveal writing that has been added with a different ink, or has been altered or removed by exploiting variations in the way different inks respond to different wavelengths of light. For example, under certain light sources combined with an infrared filter, a document containing information written in ink that has faded over time may be enhanced or processed to appear darker and therefore more legible.The main method of non-destructive ink analysis ismicro-spectrophotometry. This involves scanning the ink with ultraviolet or infrared light to record its spectrum, that is, the wavelengths of light it absorbs. Some inks fluoresce, or emit light, on exposure to ultraviolet, while others disappear. Each ink should give a distinct pattern or spectrum on exposure to ultraviolet or visible light. Put simply, this is a way of discovering the true "color" of the ink. The spectrum of the ink on the document can therefore be compared with the spectra of standard inks. Other non-destructive or minimally destructive methods, such as Ramanspectroscopy, can be used to supplement micro-spectrophotometry. It can be very informative to scan the document with infrared light because, at high frequencies, ink is invisible but pencil marks which may lie underneath will show up.

2. How does ink analysis helps in forensic investigation?Differentiating inks can be important in cases where a document is suspected of having been altered. Ingredients of the ink which are not coloured dyes can be seen using ultraviolet or infra-red light. Comparisons of the ingredients can reveal different pen types. Changes to the ink 'recipe' by manufacturers can also help to specify a pen type or sometimes prove when something was written.

3. What are the advantages and disadvantages of using TLC in ink analysis?Thin-layer chromatography (TLC) is one of the simplest techniques in separation chemistry. It is inexpensive, simple to perform and one of the most common chromatographic methods in the forensic laboratory. This is one of the few destructive techniques employed by the document examiner. The main method of destructive testing of ink is known asthin layer chromatography(TLC). In reality, it is not very destructive to the document if done with care. However, a photographic record of the original document is taken before the procedure is started. A tiny sample of the inked paper is punched out using a thin, hollow needle; a hypodermic syringe is ideal. The investigator avoids places where the pen has changed direction or where ink lines meet. This avoids any interference with subsequenthandwriting analysis. The sample is placed in a test tube with a solvent that dissolves the ink. Next, a tiny spot of the sample solution is placed onto a strip of paper, alongside spots from various reference ink samples. The paper is placed in a beaker containing a small amount of another solvent. It is positioned so that the paper dips into the solvent but the spots of sample remain dry. The solvent is drawn up the paper through capillary action and the sample spots move up with it.Chromatographymeans "writing with colors" and the chemical components of the ink, which are, of course, colored, travel with the solvent at a speed that depends upon their composition. The end result with TLC is a pattern of colored spots, known as a chromatogram, for each ink. Different inks will have different chromatograms. If the sample ink has the same chromatogram as one of the reference inks, it suggests they are the same, and soidentificationcan be made. The United States Secret Service has a reference ink database and the U.S. Treasury has a database of ink thin layer chromatograms which can be very informative.Require simple sample extraction and easy to perform; however, it has disadvantages. First, thin-layer chromatography is not typically automated; thus the spotting of a slide and the measuring of retardation factor (Rf) values are difficult to reproduce. In addition, spectroscopic data is not obtained, although densitometry can be used to analyze spots for quantitative data when compared to a standard, assuming that the chemical identity is known (Aginsky 1994). Oftentimes the spots are faint, rendering them hard to see. In this case, the spots can readily disappear in a matter of minutes. If an ink sample is composed of two or more similar dyes, then thin-layer chromatography can result in two or more unresolved spots with nearly identical colors. This scenario requires multiple runs with different solvent systems, which is time-consuming. Thin-layer chromatography reference slides should be stored in a special environment to prevent spot fading, which requires control of such factors as humidity and ultraviolet radiation exposure. In some cases, photographs of slides may alleviate the need to store reference slides