LABORATORY EXPERIMENT pubs.acs.org/jchemeduc
Using a Flatbed Scanner To Measure Detergency: A Cost-Effective Undergraduate Laboratory J. A. Poce-Fatou,*,† M. Bethencourt,‡ F. J. Moreno-Dorado,§ and J. M. Palacios-Santander|| Departamento de Química Física, Facultad de Ciencias, ‡Departamento de Ciencias de los Materiales e Ingeniería Metalurgica y Química Inorganica, Centro Andaluz de Ciencia y Tecnología Marinas, §Departamento de Química Organica, Facultad de Ciencias, and Departamento de Química Analítica, Facultad de Ciencias, Polígono del Río San Pedro, 11510, Puerto Real (Cadiz), Spain
)
†
bS Supporting Information ABSTRACT: The efficiency of a laundry-washing process is typically assessed using reflection measurements. A spectrometer and an integrating sphere are used to obtain the reflection data. The similarities between this equipment and a commercially available flatbed scanner are examined, and the way a flatbed scanner can be used to obtain detergent efficiencies is described. A flatbed scanner can be viewed as a singular spectrometer capable of obtaining spectral information concentrated in three regions of the visible spectrum. These data are stored in image files as coordinates in the redgreenblue (RGB) space where colors are represented by mixture of red, green, and blue in an 8-bit scale, that is, in a range where the intensities of these colors vary from 0 to 255. Detergent efficiencies calculated with these devices are compared. Washing tests on linseed-oil-impregnated white polyester fabrics are performed using sodium dodecyl sulfate with mass concentrations ranging from 0.00 to 1.00%. The results demonstrate that a flatbed scanner is a valuable and economical alternative to calculate detergent efficiencies in a wide variety of circumstances. KEYWORDS: First-Year Undergraduate/General, Second-Year Undergraduate, Interdisciplinary/Multidisciplinary, Laboratory Instruction, Physical Chemistry, Hands-On Learning/Manipulatives, Applications of Chemistry, Laboratory Equipment/Apparatus, UVVis Spectroscopy
T
here are many factors that must be considered when designing a laboratory experience for undergraduate students. Most factors should be pedagogical arguments; however, economical limitations cannot be ignored. Economical limitations were a motivating factor in the adaptation of a laboratory experiment to illustrate the physicochemical principles of detergency: an experiment that was designed to study the influence of surface tension, temperature, mechanical work, type of water, composition of the detergent, and so forth. Detergents are used by everyone and thus provide a learning context to introduce concepts in physical chemistry. A lecture intended to help students understand why it is easier to wash dirty dishes if they have been previously immersed in water, why we use bath sponges, or why we rub our hands together when we wash them with soap and water has been described in this Journal.1 Detergent products have at least one component exhibiting surface activity, a surfactant, and, in many cases, nonsurfactant chemicals known as builders whose key role is to remove ions that interfere with surfactants. A laboratory experience was designed to illustrate how surfactants and builders work in a washing process and was described in this Journal.2 The efficiencies of washing tests on white polyester fabrics stained with linseed oil were compared by examining the reflection of impregnated samples before and after a washing process. The Copyright r 2011 American Chemical Society and Division of Chemical Education, Inc.
reflections were measured using an Ocean Optics USB4000-VISNIR spectrometer connected to an ISP-REF integrating sphere through an optic fiber cord and controlled by the software Spectrasuite. The cost of this equipment motivated us to seek a less-expensive alternative, which was realized in a flatbed scanner. The use of scanners and digital image analysis to obtain absorbances in liquid samples was recently described in this Journal.3,4 This work shares many of the same principles but focuses them into the measure of reflections. The experiment described here is part of a larger experiment that is executed over six four-hour lab periods to study the influence of different experimental parameters in detergency (see the Supporting Information). It is a general chemistry laboratory for undergraduate students with the aim to introduce students to systematic research. This part of the experiment has been conducted by 15 students in 1.5 h.
’ REFLECTION EQUIPMENT There are several parallels between a flatbed scanner and the reflection equipment composed of a spectrometer and an Published: June 08, 2011 1314
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Table 1. RGB Coordinates of White, Yellow, and Green Fabrics channel
Figure 1. Reflection spectrum of a linseed-impregnated white polyester fabric.
Figure 2. Standard RGB filter transmittances.
integrating sphere. To analyze these similarities, we examine how the latter works. Spectrometers are usually employed to measure absorbance or transmittance in fluid media; however, they are also able to measure reflections from solid surfaces. An integrating sphere, that is, an enclosure in which light is evenly spread over its inner surface, is a proper device to perform these measurements. Despite the name, integrating spheres do not need to be spherical. We used an Ocean Optics sphere (parallelepiped) with a sample port diameter of 10.32 mm and an inner illuminating source in the range 3601000 nm.5 When the sample is placed in the integrating sphere, its specular and diffuse reflection goes through an optical fiber cord to the spectrometer. There, it is dispersed along a line where a 16-bit charge-couple device (CCD) matrix measures the intensity at each wavelength.6 With these intensities, the reflections are calculated as a percentage relative to a reference sample. For example, the spectral distribution, that is, the reflection spectrum of a linseed-impregnated white polyester fabric measured with a nonimpregnated sample as reference, is shown in Figure 1.
’ FLATBED SCANNER A flatbed scanner has a glass pane and a lid. When the lid is closed, the scanner can be described as an integrating parallelepiped, which is the first similarity with an integrating sphere. Another comparable characteristic is its light source; similar to
white sample
impregnated yellow sample
green sample
red
255
255
0
green blue
255 255
255 0
255 0
the ISP-REF integrating sphere, scanners work with an inner white light that is usually a cold-cathode or a fluorescent lamp.7 However, contrary to a spectrometer, in the scanner the light reflected by the sample is not dispersed but focused by a lens through red, green, and blue (RGB) filters with center wavelengths of around 630, 530, and 450 nm, respectively, and widths of 50100 nm fwhm8,9 (Figure 2). From the filters, light travels to CCD line sensors whose elements translate the incident radiation to an electrical signal that is digitized by an analog-todigital converter. The output of the sensors does not match an objective standard. The output depends upon the spectral reflectance of the color specimen and also upon the spectrum of the lamp, the spectral transmittance of the color filters, the spectral sensitivity of the CCD line, and the spectral response of other optical elements. To take all these factors into account, the sensors' output is numerically compensated through a color conversion circuit that performs a standardized color conversion into the RGB space where colors are represented by 8-bit (0255) integer triplets. Once the sample has been scanned, these RGB coordinates are stored into a digital image file that can be manipulated by different software.
’ RGB COORDINATES AS AN APPROXIMATION TO REFLECTIONS In the RGB space, white corresponds to (255,255,255) and black corresponds to (0,0,0). Red is (255,0,0), green is (0,255,0), and blue is (0,0,255). Secondary colors are those generated by mixture of the primary colors: yellow (255,255,0) is red plus green, cyan (0,255,255) is green plus blue, and magenta (255,0,255) is red plus blue. With the aim of using the scanner to obtain data comparable to reflections, access to the RGB information in the image file is needed. For example, to analyze the efficiency of washing tests carried out on white solid fabrics impregnated with a yellow substance, the RGB mean values of a nonimpregnated sample that, as indicated above, will be given by coordinates close to (255,255,255) is needed. Then the impregnated sample whose coordinates will be close to (255,255,0) is measured. Comparing the RGB mean values of both samples (Table 1), it is clear that in the area covered by the yellow substance the intensities of the red and green primary colors do not change. However, data of the mean intensity of blue is inversely related to the surface stained with yellow. Note that this example is useful to understand why laundry blue (also known as bluing or washing blue) is used to improve the appearance of white fabrics: blue is what is needed to convert yellowish laundry into whiter laundry (Table 1). Yet, blue will not always inform us about detergency. The selection of the primary colors that can inform us about the different levels of dirt covering a fabric depends upon the color of the fabric and the color of the dirt. For example, if the fabric was green instead of white and the stain was yellow, the primary color to observe (Table 1) would be red because neither the green nor 1315
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Figure 3. Scanned images of a reference sample (REF), a linseed-oilimpregnated sample (D), and the same sample after it was washed with a 0.6% SDS solution (C).
Table 2. Mean RGB Coordinates of a White Reference Sample and a Sample Saturated with Linseed Oil channel red
ref sample
sample satd with linseed oil
248.28 ( 0.01
245.60 ( 0.09
green
248.28 ( 0.01
246.96 ( 0.52
blue
248.49 ( 0.01
217.17 ( 0.21
the blue intensity would show changes when the fabric was washed.
’ CALCULATING DETERGENCY To compare the detergent efficiencies (DE) calculated with the devices described above, washing tests were performed at 25 °C in 200 mL of distilled water with sodium dodecyl sulfate (SDS) mass concentrations ranging from 0.00 to 1.00%. The washing tests were 15 min in duration and were carried out in duplicate using 2.0 2.5 cm white polyester pieces of fabric impregnated with linseed oil in 500 mL magnetically stirred beakers (details in the Supporting Information). Sample reflections were measured before and after the washing at 456.8 nm (Figure 1) using the equipment by Ocean Optics. The efficiency of each test was calculated by DE ¼
RC RD 100% RREF RD
ð1Þ
where R represents reflections, C refers to the cleaned sample, D refers to the dirty (oil-impregnated) sample, and REF to a reference (nonimpregnated) sample.10 Scanner images of the samples were obtained before and after they were washed (Figure 3). They were color jpg files using standard encoding and the lowest-compression, best-quality conditions, with a commercially available all-in-one HP PSC 1315 flatbed scanner at a resolution of 200 dots per inch. Tiff files, a lossless format, were also successfully used by Soldat and co-workers.4 The free software JMicroVision v1.2.511 was used to obtain the mean intensity values of the primary colors on an area of 120 150 pixels. RGB mean values of the 42 samples used in the experiments are shown in Table 2. In the RGB space, the maximum difference between the fabric white color and the greenishyellow color of the prewashed oil-impregnated samples is in the blue channel. Thus, the DEs of each test were also calculated with eq 1, but the mean intensity values of the blue coordinate in the RGB space were substituted for the reflections. The DEs calculated with both methods are displayed versus the SDS mass concentration in Figure 4. Both data sets show similar trends that differ in their absolute values. The similarity in the trends is observed because the blue filter in the scanner allows wavelengths below ∼500 nm to pass. Therefore the mean
Figure 4. Detergent efficiencies versus the SDS mass concentrations obtained by reflections (squares) and the blue coordinate in the RGB space (triangles).
intensity of the blue channel in the RGB space is related to the absorption band observed in the linseed oil spectrum (Figure 1). The difference in their mean values is due to the different spectral response of the optical elements constituting both equipments.
’ HAZARDS Sodium dodecyl sulfate is a flammable solid. It causes eye and skin irritation and may cause respiratory tract irritation. ’ SUMMARY A flatbed scanner can be considered as a useful tool to measure detergency and a valuable and economical alternative to the equipment consisting of a spectrometer and an integrating sphere. The detergent efficiency value is easily calculated with only two scans. To know which RGB channel is used under new circumstances, that is, with different fabrics or a different dirt, a digital scanner image of a reference sample is needed, then an image of the sample saturated with the dirt, and finally, the RGB coordinates of both files are compared to choose the channel that will be of value to appreciate changes in the samples. ’ ASSOCIATED CONTENT
bS
Supporting Information Additional material that shows the learning context where we apply the technique described in the article. This material is available via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
’ ACKNOWLEDGMENT Thanks are due to Gemma Torres and the Torres Prada Group for the polyester fabric samples supplied. Research supported by Universidad de Cadiz under grant Proyecto Europa IE03. ’ REFERENCES (1) Poce-Fatou, J. A. J. Chem. Educ. 2006, 83, 1147–1151. 1316
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(2) Poce-Fatou, J. A.; Bethencourt, M.; Moreno, C.; Pinto-Ganfornina, J. J.; Moreno-Dorado, F. J. J. Chem. Educ. 2008, 85, 266–268. (3) Kohl, S. K.; Landmark, J. D.; Stickle, D. F. J. Chem. Educ. 2006, 83, 644–646. (4) Soldat, D. J.; Barak, P.; Lepore, B. J. J. Chem. Educ. 2009, 86, 617–620. (5) Ocean Optics. ISP-REF Integrating Sphere; http://www. oceanoptics.com/products/ispref.asp (accessed May 2011). (6) Ocean Optics. USB4000. Fiber Optic Spectrometer. Installation and Operation Manual; http://www.oceanoptics.com/technical/ USB4000operatinginstructions.pdf (accessed May 2011). (7) Thomas, G.; Chu, R. Y. L.; Rabe, F. J. Appl. Clin. Med. Phys. 2003, 4, 307–314. (8) Korte, L.; Bastide, S.; Levy-Clement, C. Sol. Energy Mater. Sol. Cells 2008, 92, 844–850. (9) Suzuki, S.; Kusunoki, T.; Mori, M. Appl. Opt. 1990, 34, 5187– 5192. (10) Cramer, J. J. Detergency. Theory and test methods; Marcel Dekker, Inc.: New York, 1972; pp 323411. (11) Roduit, N. JMicroVision: Image analysis toolbox for measuring and quantifying components of high-definition images, Version 1.2.5; http://www.jmicrovision.com (accessed May 2011).
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