Microsoft Word - 124-144 https://doi.org/10.30526/31.1.1860 Chemistry | 124 2018) عام 1دد (الع 13مجلة إبن الهيثم للعلوم الصرفة والتطبيقية المجلد Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Determination of the Degree of Consumption (DoC) of Lube Engine Oils Using Fluorescence Spectroscopy Rawnaq Qahtan Abdul Kareem Khalid W. Salih Al-Janabi Dept of. Chemistry/ College of Education for Pure Science (Ibn Al- Haitham)/University of Baghdad Raonaq_1993@yahoo.com khalid.janabi@gmail.com Received in: 3/October/2017, Accepted in:3/December/2017 Abstract The accreditation of a fast, inexpensive, and simple way to discriminate between different kinds of oils and their efficacy “degree of consumption (DoC)” has been developed. The fluorescence spectroscopy provides a reliable method for oil inspection without resorting to tedious separation. Different new and used oil samples available in the local Iraqi market were investigated. While the challenge is to build a directory containing data of all the oils available in the local market. This method expected to control the falsified (forged) trademarks of motor oils and to discriminate between different oils. The excitation-emission spectra of oil samples were determined in the range of 200 – 600 nm. The effect of the presence of trace metals on the fluorescence intensity of oils was considered by adding few milligrams of (Cu, Al, Fe) to the diluted oil solution. No major effect noticed on fluorescence intensity. The research suggests installing a simple Spectrofluorometer into vehicles to check the DoC of the oil regularly and to notify the driver exactly when to replace the engine oil. The obtained results indicate the applicability to execute such gadget to be installed in the vehicles for routine detection of the engine oil quality and its degree of consumption DoC. As well as demonstrate the potential of the technique in oil identification and could be further developed. Keywords: Fluorescence, Degree of Consumption (DoC), lube oil, engine oil https://doi.org/10.30526/31.1.1860 Chemistry | 125 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Introduction The lube oil composition is a complex mixture of hydrocarbons with different molecular masses. The lube oil producers generally use the same base-stock then add different additives up to 5% by weight [1] to improve the oil performance [2]. Lube oils are designed to lubricate the moving parts of internal combustion engines to reduce friction, provide oxidation resistance, improved deposit protection, better wear protection, better low-temperature performance over the life of the oil [2] and protect the engine from malfunctions [3]. Thus, oil testing is important to examine lubricant's quality and to discriminate between new and used oils [4]. Because of the complexity of lube oils and the many factors affecting their compositions, almost all analyses been partial and not very accurate [5]. Exhausted motor oils are hazardous wastes to the environment [6] and could reach the sources of drinking water and crops irrigation [7]. Most of the lubricants absorb UV or visible light, while few are fluorescent [8]. Organic molecules such as oils, with extended π-electron systems as for aromatic and some unsaturated aliphatic compounds, often exhibit fluorescence efficiency [9]. Compounds containing fused-rings usually exhibit high molecular fluorescence [10]. Rigid molecules or multiple ring systems tend to have large quantum yields of fluorescence while flexible molecules generally have lower quantum yields [11]. Fluorescence detectors are very selective and are about three orders of magnitude more sensitive (0.001–0.01 ng) than UV detectors as they measure the fluorescence of the analyte against an almost zero background [12]. There are many other applications for fluorescence spectroscopy, not limited to; determination of thermal stability of biocatalysts, Characterizing bio labels for live cell imaging, Hydrocarbon mixtures in petroleum oils, and Characterizing GPCR (G protein– coupled receptors) oligomerization [13]. Nevertheless, many other applications in Nanoparticle characterization, Surface chemistry research, Analytical chemistry, Pharmacology, Biotechnologies, and in crime investigation [14]. Most fluorescence measurements use to carry out in liquid media and the solutions must be very dilute in fluorimetry. Otherwise, the results may not comply with the Lambert–Beer law and linearity cannot be achieved [15]. This leads to the apparently paradoxical result that the fluorescence can diminish even though analyte concentration increases. Molecules that naturally fluorescence inactive can convert by chemical derivation or by reacting with a fluorescent molecule to become fluorescent. The interaction of a fluorescent molecule with the solvent medium will affect both the energy and intensity of fluorescence spectra. Effects of polarization and hydrogen bonding, viscosity effects, heavy atom effect, compound formation and photo-reaction have a critical influence on the resultant fluorescence [16]. In polar media, fluoresce molecules may solvate by dipolar attraction. These effects produce differences in the equilibrium configurations of the ground and excited states [17]. The solvent can also interact with fluorophores to form excited state complexes that do not fluoresce. Selection of a solvent to minimize this effect can enhance fluorescence. In addition to the absorption and emission, Scattering may happen either due to Rayleigh scattering or by small particles in colloidal suspension (Tyndall scattering) [18]. Some of the incident energy transferred to the solvent molecules in the form of vibrational and rotational energy. Then re- emitted in longer wavelength and less energy than the excitation radiation. This is called Raman scattering, which is 100 to 1000 times weaker than Rayleigh’s [19]. Unlike absorption – emission fluorimetry is synchronous fluorescence scan (SFS), in which both monochromators moves simultaneously [20]. The synchronous technique allows the stronger peaks to be increased selectively by use of a suitable stoke shift Δλ [21]. Unlike UV/visible spectroscopy, fluorescence may undergo quenching, which is a reduction in fluorescence intensity [22]. One reason for quenching is the molecular interaction when a https://doi.org/10.30526/31.1.1860 Chemistry | 126 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 fluorophore is in contact with another molecule. Other reasons lead to a loss of emission from the fluorophore include energy transfer, charge transfer reactions or photochemistry [23]. The final goal of this study is to develop a sensing system uses a simple fluorometer, which can be installed in the vehicle to determine the DoC and to notify the driver when to replace the engine oil. This will ensure changing the oil only when fully depleted, which reduces costs and preserve the environment. The reliance on the car mileage counter to replace the engine oil is not accurate enough since the consumption of oil (DoC) depends on many factors not limited to oil quality, climate, driving habit, engine efficiency, etc. Nevertheless, discrimination the quality of lube oils is of great importance as well. Experimental Part Instrumentation  Cary Eclipse Fluorescence Spectrophotometer G9800A, Agilent Technologies, USA.  Varian Cary Peltier Multicell 4 Position Cell Holder, G9808-00003, Agilent technologies, USA.  Quartz cuvettes with four clear faces.  Digital Analytical balance, Sartorius GD503 (0.0001g), Germany.  Analog Water Bath, Labtech, Vietnam. Materials and reagents  Several motor oils from different producers available in the Iraqi market over the period Oct 2016 to May 2017, Error! Not a valid bookmark self‐reference.1.  Benzene (97%, BDH), Cyclohexane (99.7%, BDH), Chloroform (99.4%, Merk), Dichloromethane (98.8%, Fluka), Ethanol absolute (99.9%, BDH), n-hexane (99.9%, Scharlau), Toluene (99.5%, Himedia).  Heavy metals (Cu, Fe, Al) as fine powders, obtained from local workshops. https://doi.org/10.30526/31.1.1860 Chemistry | 127 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Table (1): Codes and details of different motor oil samples examined in this study Sample Code Trademark Origin Volume (Lit) SAE API R1 Gardul Germany 5 5W-20 SL/CF R2 Youkn lraq 1 HD 50 CC/SC R3 Hanover Germany 5 5W-30 SN R4 Hanover Germany 4 20W-50 SG/CD R5 Wagon lraq 1 140 GL4 R6 Jumbo Royal Iraq 1 HD 50 CC/SC R7 Mechilon French 5 10W-30 SN R8* Morris UK 20 15W-40 HD4 R9* Vulcan UAE 5 50 CF R10 Maxpro/ Mopar USA 5 5W-20 SN R11* Acdelco USA 4 10W-30 SN R12* Quartz UAE 4 20W-50 SL R13* Petromin USA 1 20W-50 SL/CF R14* Fuchs Germany 1 20W-50 SL R15* Acdelco USA 1 5W-30 SN R16* GAT 1 USA 5 20W-50 SL  SAE: The Society of Automotive Engineers  API: American Petroleum Institute  * Samples have a used peer. Used oil samples followed by the suffix “u”. Optimization of Fluorescence Measurement Different conditions been examined as a function of the fluorescence intensity as an arbitrary unit (a.u.) to optimize the test method and increasing its sensitivity. Conditions of Emission and Excitation Wavelengths pairs (EEWs), slit width of both the excitation and the emission monochromators, adjustment of the emission path length, temperature, and the contamination by the presence of wear metals in engine oil. Degree of Consumption (DoC) for lube oil DoC has been determined for some lube oils by measuring the fluorescence intensity at a certain EEWs for each pair of the fresh/consumed oil at different proportions. https://doi.org/10.30526/31.1.1860 Chemistry | 128 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Results and Discussion Sampling Eight out of 16 oil samples collected in pairs (new/used). Solvents like strong acids, strong bases or even acetone were avoided while cleaning the quartz cuvettes as they might attach to their walls [20]. Factors affecting Fluorescence Measurements A number of parameters have been studied intensely to determine the optimized conditions. Setting up EEWs pairs Finding the right EEWs pairs is of great importance to maintain sensitivity. EEWs found automatically using the function “Prescan” available in the spectrofluorometer software. While manual recognition of the EEWs was accomplished by setting the excitation monochromator to the of the maximum wavelength (λmax) UV/Vis absorption spectrum. Then the emission monochromator is set to the highest emission intensity obtained, and scan the excitation radiation again to specify the best corresponding excitation wavelength. Both approaches gave almost the same EEWs results. Emission intensities have been compared for different couples of new/used oil samples under identical measurement conditions, as appears in Figure (1-5). Figure (1): Comparing the fluorescence spectra for 5.18 mg/l of R11 vs. R11u oil samples in benzene 0 100 200 300 400 500 600 700 800 900 1000 330 380 430 480 In te n si ty   Fluorescence emission wavelength (nm) R11 R11U https://doi.org/10.30526/31.1.1860 Chemistry | 129 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Figure (2): Comparing the fluorescence spectra for 2.59 mg/l of R13 vs. R13u oil samples in toluene Figure (3): Comparing the fluorescence spectra for 1.295 mg/l of R14 vs. R14u oil samples in hexane 0 100 200 300 400 500 600 700 800 900 1000 330 380 430 480 In te n si ty Fluorescence emission wavelength (nm) R13 R13U 0 100 200 300 400 500 600 700 800 900 340 390 440 490 In te n si ty Fluorescence emission wavelength (nm) R14 R14U https://doi.org/10.30526/31.1.1860 Chemistry | 130 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Figure (4): Comparing the fluorescence spectra for 1.295 mg/l of R15 vs. R15u oil samples in hexane Figure (5): Comparing the fluorescence spectra for 2.59 mg/l of R16 vs. R16u oil samples in hexane   Setting up the radiation slits widths The best slit width of both the excitation and the emission monochromators were tested by changing the slit width of both monochromators individually. Better sensitivity obtained with wider slit widths. However, if the priority is to selectively discriminate a specific analyte in a mixture then, the usage of narrower slits will be necessary [17] [24]. As it is clear from the figure (6); that the optimized value for the excitation-slit width was 10 nm while the best emission-slit width was 5 nm. However, the emission intensity was out of scale when both excitation and emission slits widths were set to 10 nm. 0 100 200 300 400 500 600 700 800 900 1000 260 310 360 410 460 In te n si ty Fluorescence emission wavelength (nm) R15 R15U 0 100 200 300 400 500 600 700 800 900 330 380 430 480 In te n si ty  ( a .u .) Fluorescence emission wavelength (nm) R16 R16U https://doi.org/10.30526/31.1.1860 Chemistry | 131 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Figure (6): Overlay fluorescence spectra for the following slits widths a: (ex10, em5), b: (ex5, em5), c: (ex10, em2.5), d: (ex2.5, em5) in nm. Oils were dissolved in ethanol. The influence of emission path length The emission path length is the perpendicular distance between the excitation beam passing through the sample and the cuvette facet facing the detector. Longer paths may lead to self-quenching caused by the unexcited molecules between the fluorescent analytic and the emission detector those may absorb the emitted light [23]. When an engine oil consumed, it become darker, then a shorter path length will be a good solution to reduce the optical density. A Varian Peltier Multicell 4 Position Cell Holder, figure (7), used to control the emission path length so that the incident beam passes closer to the cuvette face in front of the detector. This will shorten the thickness facing the detector, figure (8). Figure (7): Varian Peltier Multicell 4 Position Cell Holder from Agilent Technology; a) a top view, b) partially dissembled, x) manual fine adjustment knob https://doi.org/10.30526/31.1.1860 Chemistry | 132 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Figure (8): Controlling the emission path length by shifting the cuvette The multicell holder has been dissembled partially to enable controlling the cell position manually; this made the adjustment very easy and accurate by turning a fine adjustment knob. The effect of the cuvette position has examined as a function of the fluorescence intensities obtained, table (2). From the Figure (9-10), the fluorescence intensity of the oil samples is inversely proportional to the emission path length facing the detector. This been expected, as the number of the unexcited molecules existing in the emission path those causing quenching by absorbing the fluorescent light is reduced. Table (2): The emission intensity of R11 oil sample vs. path length Intensity (A.U.) Emission wavelength (nm) Emission Path length (mm) 498.195 535.07 1 551.822 531.04 2 530.776 531.94 4 510.339 531.94 5 442.854 528.05 6 281.476 521.94 7 252.306 525.97 9 https://doi.org/10.30526/31.1.1860 Chemistry | 133 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Figure (9): Fluorescence intensity of the oil samples is inversely proportional to the emission path length facing the detector Figure (10): Fluorescence intensity versus emission path length Temperature effect Oil samples were tested over a range of temperature (10 to 50) C° as a function of their emission intensity, Error!  Reference  source  not  found.11-14. Nevertheless, some oil samples did not exhibit fluorescence activity when tested at ranges of (35-50) C°, which may relate to the loss of rigidity. As the molecules, those excited to a higher electronic excited state may lose their electronic energy by converting it to vibrational without emitting radiation [15]. y = ‐6.7637x2 + 29.034x + 502.07 R² = 0.8602 200 300 400 500 600 0 2 4 6 8 10 In te n si ty  ( A .U .) Path length facing detector (mm) https://doi.org/10.30526/31.1.1860 Chemistry | 134 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Figure (11): Fluorescence spectra for 5.18 mg/l of R11 in benzene at different temperatures, best intensity obtained at 10 ºC Figure (12): Fluorescence spectra for 1.295 mg/l of R11u in toluene at different temperatures, best intensity obtained at 15Cº   0 200 400 600 800 1000 330 350 370 390 410 430 450 470 In te n si ty  ( a .u .) Fluorescence emission wavelength (nm) 10 c° 15 c° 25 c° 0 200 400 600 800 300 350 400 450 500 550 600 In te n si ty  ( a .u .) Fluorescence emission wavelength (nm) 10 c° 15 c° 25 c° 30 c° 35 c° 40 c° 45 c° 50 c° https://doi.org/10.30526/31.1.1860 Chemistry | 135 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Figure (13): Fluorescence spectra for 1.295 mg/l of R15 in hexane at different temperatures. The best intensity obtained at 50Cº Figure (14): Fluorescence spectra for 2.59 mg/l of R15u in hexane at different temperatures. The best intensity obtained at 40Cº 0 200 400 600 800 1000 260 310 360 410 460 510 560 In te n si ty  ( a .u .) Fluorescence emission wavelength (nm) 10 c° 15 c° 25 c° 30 c° 35 c° 45 c° 50 c° 0 200 400 600 800 1000 300 350 400 450 500 550 600 In te n si ty  ( a .u .) Fluorescence emission wavelength (nm) 10 c° 15 c° 25 c° 30 c° 35 c° 40 c° 45 c° 50 c° https://doi.org/10.30526/31.1.1860 Chemistry | 136 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Metal Contamination Engine oil contaminates with some metals produced as a result of the friction of the rubbing of the moving mechanical metallic parts of the engine. This may affect the fluorescence activity of the lube oil due to increased rigidity when some organic chelating agents complexes with a metal ion. Accordingly, small amounts of the metals those expected to compose the engine alloy (aluminum, iron, and copper) added to the lube oil samples to examine their effect as a function of fluorescence activity, figure (15-20). The examined effects were not significant. Figure (15): Fluorescence spectra for 5.18 mg/l of R11 in benzene with traces of different metals 0 200 400 600 800 1000 330 380 430 480 530 580 In te n si ty  ( a .u .) Fluorescence emission wavelength (nm) Without metal With AL With Cu With Fe https://doi.org/10.30526/31.1.1860 Chemistry | 137 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Figure (16): Fluorescence spectra for 1.295 mg/l of R11u in toluene with traces of different metals Figure (17): Fluorescence spectra for 1.295 mg/l of R15 in hexane with traces of different metals   0 200 400 600 800 1000 300 350 400 450 500 550 600 In te n si ty  ( a .u .) Fluorescence emission wavelength (nm) Without metal With AL With Cu With Fe 0 200 400 600 800 1000 240 340 440 540 In te n si ty  ( a .u .) Fluorescence emission wavelength (nm) Without metals With Al With Cu With Fe https://doi.org/10.30526/31.1.1860 Chemistry | 138 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Figure (18): Fluorescence spectrum for 2.59 mg/l of R15u in hexane with traces of different metals Figure (19): Fluorescence spectra for 2.59 mg/l of R16 in hexane with traces of different metals 0 200 400 600 800 1000 300 350 400 450 500 550 600 In te n si ty  ( a .u .) Fluorescence emission wavelength (nm) Without metals With Al With Cu With Fe 0 200 400 600 800 1000 330 380 430 480 530 580 In te n si ty  ( a .u .) Fluorescence emission wavelength (nm) Without metals With AL With Fe With Cu https://doi.org/10.30526/31.1.1860 Chemistry | 139 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Figure (20): Fluorescence spectra for 1.295 mg/l of R16u in hexane with traces of different metals Direct measurement of fluorescence The fluorescence of all oil samples was measured directly without dilution. The selected EEWs were obtained by the function “Prescan” for each oil separately, Figure (21). The excitation and emission slits widths were 5 nm for both monochromators. The temperature was controlled to 24±1C° during measurements. The resultant intensity for each oil sample considered as the 100% intensity of the fresh new oil which can be used for later comparison, table (3). 0 200 400 600 800 300 350 400 450 500 550 600 In te n si ty  ( a .u .) Fluorescence emission wavelength (nm) With Fe With AL With Cu Without metals https://doi.org/10.30526/31.1.1860 Chemistry | 140 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Figure (21): Pre-scan fluorescence spectrum of R1 oil sample Table (3): Fluorescence spectra for new motor oils Oil Sample Excitation (nm) Emission (nm) Intensity (a.u.) R1 464 510 319 R2 532 583 344 R3 386 481 750 R4 408 442 387 R5 408 442 387 R6 532 583 283 R7 474 514 554 R8 464 473 73 R9 494 535 339 R10 462 532 206 R11 464 528 501 R12 462 503 562 R13 464 509 184 R14 350 578 465 R15 462 527 474 R16 462 499 830 https://doi.org/10.30526/31.1.1860 Chemistry | 141 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Degree of Consumption (DoC) of lube oil Direct measurement of lube oil without the need for any sample preparation with no residues generated and a very short analysis time is of great significance. The fluorescence intensity was examined for 1.5 mL of new oil samples after spiked by different aliquots of consumed oil of the exact same brand and type. These tests were carried out in optimized conditions to test the DoC. table (4), figures (22-31). Table (4): Fluorescence intensity versus the spiked volume for some New/Used oil couples. As the table is very long some records those not affecting the overview have omitted Oil Sample Volume of consumed oil (ml) Excitation (nm) Emission (nm) Stokes shift Intensity (a.u) DoC % R11 0 464 540 76 501 0% R11 0.05 464 540 76 332 34% R11 0.1 464 540 76 298 41% R11 0.75 464 540 76 4 99% R12 0 462 511 49 562 0% R12 0.05 462 511 49 317 44% R12 0.1 462 511 49 205 64% R12 0.9 462 511 49 3 99% R14 0 530 581 51 465 0% R14 0.05 530 581 51 403 13% R14 0.1 530 581 51 385 17% R14 2.35 530 581 51 7 98% R15 0 462 514 52 474 0% R15 0.05 462 514 52 387 18% R15 0.1 462 514 52 331 30% R15 0.65 462 514 52 7 99% R16 0 462 506 44 830 0% R16 0.05 462 506 44 543 35% R16 0.1 462 506 44 325 61% R16 2.1 462 506 44 4 100% For each oil sample, the fluorescence intensity has been drawn against the added volume portions of the peer used oil. The slope and the linearity obtained from the sketch of the second order polynomial function for the curve represents DoC and the oil quality, i.e. higher slope and R2 values means better oil quality, figure (22). However, the suggested relation between DoC and the sample composition became clearer by plotting the value of logarithm to the base ten of the DoC against the added volume of consumed oil, then getting the exponential trend line of the curve, figure (23). The resultant slope and linearity values represent the oil quality since high values mean the oil preserve lubricating properties and can endure larger volumes of the consumed residues without changing its properties. Therefore, the next graphs conclude that the oil coded R14 has the best quality than the other samples since it has the highest values for slope, table (5). https://doi.org/10.30526/31.1.1860 Chemistry | 142 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Table (5): A comparison for the quality of some oil samples as a function of the corresponding slope and linearity extracted from the graphs of the fluorescence intensity of fresh oils (1.5 ml each) versus the added volume of its peer consumed oil Figure (22): A comparison for the fluorescence intensity of some fresh oils (1.5 ml each) versus an added volume of its peer consumed oil 0 100 200 300 400 500 600 700 800 900 0.00 0.50 1.00 1.50 2.00 2.50 In te n si ty  ( a .u .) Added volume of consumed oil (ml) R11 R12 R14 R15 R16 Oil Sample Emission (nm) Before Log(10) After Log(10) Slope Linearity R^2 Slope Linearity R^2 R11 540 -217.3700 0.7001 0.6285 0.989 R12 511 -121.9400 0.535 0.9729 0.976 R14 581 105.2100 0.612 55.2345 0.968 R15 514 -320.0300 0.720 0.3950 0.961 R16 506 98.7300 0.483 32.3665 0.963 https://doi.org/10.30526/31.1.1860 Chemistry | 143 2018) عام 1دد (الع 13لمجلد ا مجلة إبن الهيثم للعلوم الصرفة والتطبيقية Ibn Al-Haitham Jour. for Pure & Appl. Sci. Vol. 31 (1) 2018 Figure (23): A comparison for the logarithmic scale to the base 10 of fluorescence intensity of some fresh oils (1.5 ml each) versus an added volume of its peer consumed oil Conclusion The experimental findings have indicated that fluorescence spectroscopy is easy, affordable, sensitive, fast, and an efficient way to identify and discriminate between different lube oils. As the measured fluorescence intensity of the of the new and used oil samples is proportional to the degree of consumption DoC of the oil. In addition, DoC is applicable and can be of great economic and environmental benefit. The major obstacle in this study is the lack of an updated indexed library implying data of all oils available in the local market. Such data is vital for oil comparison and verification. References [1] J.H. Christensen; A.B. Hansen; J. Mortensen; O. Andersen, Characterization and matching of oil samples using fluorescence spectroscopy and parallel factor analysis, Anal. Chem. 77 2210–2217. 2005 [2] S.Q.A. Rizvi; A. Comprehensive Review of Lubricant Chemistry, Technology, Selection, and Design, University of Virginia, Virginia, 2008. [3] R. Haycock; A. Caines; J. Hillier; Automotive lubricants reference book, 2nd ed., 2004. [4] R.A.K. Nadkarni, Spectroscopic Analysis of Petroleum Products and Lubricants, Bridgeport, 2011. [5] J. Steffens; E. Landulfo; L.C. 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