Talanta 81 (2010) 1096–1101 Contents lists available at ScienceDirect Talanta journal homepage: www.elsevier.com/locate/talanta Application of chemometrics and FTIR for determination of viscosity index and base number of motor oils Mohammad Ahamd Al-Ghouti a,∗ , Yahya Salim Al-Degs b , Mohammad Amer a a Royal Scientific Society, Industrial Chemistry Centre, P.O. Box: 1438 Amman 11941 Jordan b School of Chemistry, Hashemite University, Zarqa, Jordan article info Article history: Received 9 November 2009 Received in revised form 31 January 2010 Accepted 1 February 2010 Available online 6 February 2010 Keywords: Motor oil Base number Viscosity index Multivariate calibration ASTM FTIR abstract The viscosity index (VI) and the base number (BN) of motor oils are the most important parameters to be measured in order to assess their performance and service time. Both parameters were simply obtained for virgin and recycled motor oil samples using multivariate calibration based on the FTIR data. Analysis showed that the PLS-1 has outperformed CLS and PCR for the oil parameters predic- tion. Five and four PLS-1 latent variables were found optimum to obtained the VI and the BN from the FTIR data; respectively. With high accuracy (99–102%) and precision (3–11%), the BN could be deter- mined over the range 4.57–16.45 mg KOH g -1 and the VI over the range 96–153. The outputs of the PLS-1 were found comparable to those obtained by the expensive and time-consuming ASTM meth- ods. This developed method is highly recommended for quick monitoring of the motor oil quality parameters. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Motor oil is vital for maintaining optimum engine performance [1]. Motor oil has many valuable functions, these include: (1) protecting the engine from the effects of heat, pressure, corro- sion, oxidation and contamination, (2) providing a fluid barrier between moving parts, reducing friction and wear, (3) cleaning the interior of the engine by removing dirt, wear and combus- tion contaminants [1,2], and (4) cooling an engine by increasing heat dissipation, further reducing wear and preventing the entry of contaminants. Motor oil mainly consists of two materials, which are the base oil and chemical additives. Various types of additives are blended with base oil according to its grade and specific duty such as metallic detergents, ashless dispersants, zinc dithiophos- phate, anti-oxidant/anti-wear, friction modifier, viscosity modifier, antifoam and pour point depressant [2–4]. However, the purpose of detergents in crankcase oils is: (a) to suspend/disperse oil-insoluble combustion products, such as sludge or soot and oxidation products, (b) to neutralise com- bustion products (inorganic acids), (c) to neutralise organic acids products of oil degradation processes and (d) to control rust, cor- rosion and deposit-forming resinous species [5,6]. Therefore, it ∗ Corresponding author. Tel.: +962 65344701; fax: +962 65344806. E-mail address: mghouti@rss.gov.jo (M.A. Al-Ghouti). is an important task to assure the motor oil quality. However, the main motor oil physicochemical characteristics are covered under the American Standards for Testing and Materials (ASTM) guides. These are: ASTM D2896 [7], ASTM D445 [8] and ASTM D2270 [9]. The base number (BN) is expressed as mg KOH g -1 of additive. It is measured using a potentiometric method (e.g., ASTM D2896 [7]). This test method covers the determination of basic constituents in petroleum products by titration with per- chloric acid in glacial acetic acid using a potentiometric titrator. This test method can be used to determine base number up to 300 mg KOH g -1 . For liquids, the viscosity increases as the temperature decreases and vice versa [10]. Variable thickness of oil by viscosity modifiers at low and high temperatures allows the formulation of multigrade oils. The multigrade oils are designed to provide adequate viscos- ity at high temperatures for engine protection and low viscosity at low temperatures for easy stability. The viscosity index (VI) is used as a measure of oil’s response to temperature changes. In addition to affecting the viscosity temperature relationship, viscosity modi- fiers affect a lubricant’s other properties. These include pour point, dispersancy and fuel economy [9]. However, the BN and the VI testing are in general slow and time-consuming and it is generally expensive in testing. In this work, a procedure for simple and accurate determination of the BN and the VI of motor oil based on the use of the FTIR analysis along with multivariate method was developed and tested. The FTIR spectroscopy is the fastest and cheapest of the spectroscopic tech- 0039-9140/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2010.02.003