Ehsan Sadia, Sedman Jacqueline, van de Voort Frederick R, Akochi-Koblé Emmanuel, Yuan Tao, Takouk Djaouida
McGill University, Ste. Anne de Bellevue, Canada.
J Lab Autom. 2012 Jun;17(3):201-10. doi: 10.1177/2211068211431108. Epub 2012 Jan 24.
An automated FTIR method for the determination of the base content (BC(pKa)) of oils at rates of > 120 samples/h has been developed. The method uses a 5% solution of trifluoroacetic acid in 1-propanol (TFA/P) added to heptane-diluted oil to react with the base present and measures the ν(COO(-)) absorption of the TFA anion produced, with calibrations devised by gravimetrically adding 1-methylimidazole to a heptane-TFA/P mixture. To minimize spectral interferences, all spectra are transformed to 2(nd) derivative spectra using a gap-segment algorithm. Any solvent displacement effects resulting from sample miscibility are spectrally accounted for by measurement of the changes in the 1-propanol overtone band at 1936 cm(-1). A variety of oils were analyzed for BC(0.5), expressed as mEq base/g oil as well as converted to base number (BN) units (mg KOH/g oil) to facilitate direct comparison with ASTM D2896 and ASTM D974 results for the same samples. Linear relationships were obtained between FTIR and D2896 and D974, with the ASTM methods producing higher BN values by factors of ~1.5 and ~1.3, respectively. Thus, the FTIR BC method correlates well with ASTM potentiometric procedures and, with its much higher throughput, promises to be a useful alternative means of rapidly determining reserve alkalinity in commercial oil condition monitoring laboratories.
已开发出一种自动傅里叶变换红外光谱（FTIR）方法，用于以每小时超过120个样品的速率测定油的碱含量（BC(pKa)）。该方法使用三氟乙酸在1-丙醇中的5%溶液（TFA/P），将其加入庚烷稀释的油中，使其与存在的碱发生反应，并测量所产生的TFA阴离子的ν(COO(-))吸收峰，校准是通过将1-甲基咪唑重量法加入庚烷-TFA/P混合物中进行的。为了使光谱干扰最小化，所有光谱都使用间隙分段算法转换为二阶导数光谱。由样品混溶性导致的任何溶剂置换效应，通过测量1936 cm(-1)处1-丙醇泛频带的变化在光谱上进行考虑。对多种油分析了BC(0.5)，以mEq碱/克油表示，并转换为碱值（BN）单位（毫克KOH/克油），以便于与相同样品的ASTM D2896和ASTM D974结果进行直接比较。FTIR与D2896和D974之间获得了线性关系，ASTM方法产生的BN值分别高出约1.5倍和约1.3倍。因此，FTIR BC方法与ASTM电位法程序相关性良好，并且由于其更高的通量，有望成为商业油况监测实验室快速测定储备碱度的一种有用的替代方法。
