The extraction and subsequent separation and quantification of polymer additives in polyolefins have proven to be a challenge for analytical chemists. [1][2][3][4][5][6][7] The quantification of additives in polymers is important in forensic investigations, scientific research and quality control. Currently, a range of additives is being used for protection during processing, increasing the lifetime and improving the performance of products. Although high-performance liquid chromatography (HPLC) is a very good method for the separation of complex additives, there are some difficulties in the identification of some components. [8][9][10][11] Gas chromatography coupled with mass spectrometry (GC-MS) is very beneficial for separating and identifying some additives, but when dealing with antioxidants and stabilizers it is not feasible in many cases, owing to their decomposition or lack of volatility. Only a few papers have been published concerning determination of some additives. Pyrolysis-GC, which needs to special instrument, is a common technique for this purpose. [12][13][14][15][16][17][18] So far, calcium stearate, which is added to polyolefins as a lubricant, was not directly determined by chromatographic techniques. It has a limited solubility in organic solvents, especially in those solvents that are used as a mobile phase or a modifier in liquid chromatography. On the other hand, calcium stearate cannot be determined by a gas-chromatographic technique due to its low volatility. In this study a gas chromatographic technique was presented for the determination of calcium stearate in polyolefin samples after its conversion to stearic acid.A recently presented extraction technique, dispersive liquid-liquid microextraction (DLLME), [19][20][21] was used to preconcentrate the analyte before its injection to GC. In this method, a solvent with a density higher than that of water at the range of microliter is used as an extracting solvent. Another solvent, such as methanol, acetonitrile, tetrahydrofuran or acetone which is miscible with both aqueous and organic solvents is added as a dispersive agent to disperse the extracting solvent into the aqueous phase. DLLME is a rapid and efficient extraction technique. It uses an extraction solvent at the mL level. In DLLME, a higher enrichment factor is achievable compared with ordinary liquid-liquid extraction techniques.
experimental
ApparatusA gas chromatograph STG Model GC 101B (Teif Gostar Co., Tehran, Iran), equipped with a flame ionization detector (FID), was used. The injection port system was a spilt/splitless injector. The characteristics of the capillary column and the GC conditions used in this analysis were as follows: column, Optima-1 (1.5 m ¥ 0.25 mm i.d.); thickness of stationary phase, 0.1 mm (Macherery Nagel, Germany); average linear velocity of nitrogen as carrier gas, 30 cm s -1 ; flow-rate of nitrogen as make up gas, 35 mL min -1 ; flow-rate of air and hydrogen for FID flame, 300 and 35 mL min -1 , respectively; temperature of the injection port, 200˚...
