Direct analysis of Ca, P, and Fe in oleochemicals by inductively coupled plasma MS

Abstract

This paper presents the use of inductively coupled plasma MS (ICP-MS) for direct elemental analysis in oleochemicals (long-chain fatty acid derivative). It focuses on Ca, P, and Fe, which are key elements for many industrial applications and which are known to be challenging for MS technology. The instrument is operated with a "shield torch" interface under "highpower cool plasma." In addition, oxygen is blended with argon to prevent buildup of carbon on both torch and cones. The extra sensitivity of the ICP-MS technology permits high dilution factors, thereby minimizing any potential matrix effects. The contents of Ca, P, and Fe are quantified by standard addition. There is no need to resort to interference corrections for P, because it is measured as its oxide PO + . Detection limits lie in the sub-ppm for Ca and P and in the low-ppb for Fe. Accuracy of the method has been demonstrated for our products by a recovery test.Paper no. J10583 in JAOCS 81, 437-440 (May 2004). KEY WORDS:Direct ICP-MS analysis of organics, oleochemicals, quantification of Ca, P, and Fe.The chemical industries require the routine trace analysis of elements, both to meet the requirements of speciality chemical markets and to monitor specific processes. The analytical tools must be able to quantify various elements from ppm to ppb in a wide range of matrices to meet the demand of food (1,2), personal-care (3), pharmaceutical (4), or electronic applications (5). In addition, control of manufacturing (6) is often limited by the rapidity of the overall analytical process. Thus, sample preparation for routine work must remain simple and quick. Despite its high purchasing cost, inductively coupled plasma-mass spectrometry (ICP-MS) (7-9) has become the method of choice for fast trace-level elemental analysis in aqueous solutions (10). However, until recently, extension of this technique to the direct quantification of elements in organic matrices has been hindered by technical issues (11-13). Its use in routine analysis is restricted to the determination in organic solvents of impurities present in the ppb range (14); these are rather simple organic products that generate a limited number of spectral interferences. When dealing with products characterized by more complex matrices, most publications still resort to extensive sample pretreatment (15-18), which is time-consuming and may lead to erroneous results due to contamination or loss of volatile elements. In a few cases only, microemulsification (including water in oil) has been reported as an alternative way of introducing organic samples (19). This paper investigates the use of ICP-MS technology for direct trace elemental analysis of oleochemicals after a simple dilution operation. These products are characterized by complex matrices, often containing relatively high levels (up to 100 ppm) of alkali and alkaline-earth metals as impurities. This study focuses on Ca, P, and Fe, which are key for many speciality chemicals and which are known to be challenging for the MS technology. They all ...