Determination of free phenol in friction layer of brake pad by gas chromatography with ultrasonic extraction
Free phenol in the friction layer of brake pads will volatilize into the air and pollute people's living environment,so it is necessary to accurately determine and control its content.After the sample was trans-ferred into a clean cryogenic grinding steel cylinder,it was frozen and pulverized into a powdered solid with particle size of 0.075-0.150 mm by liquid nitrogen.0.5-1.0 g of solid powder was weighed and treated by ultrasonic extraction for 30 min with ethanol.After dilution to the mark,the supernatant liquor was fil-tered with 0.45 μm membrane.Then it was separated with HP-INNOWax capillary column and deter-mined by gas chromatography.Consequently,the determination of free phenol in the friction layer of brake pads was realized by gas chromatography.The results showed that the concentration of free phenol in range of 2.0-200 mg/L had a linear relationship with its corresponding chromatographic peak area.The linear correlation coefficient was 0.999 5,and the limit of quantification of method was 10 mg/kg.The contents of free phenol in 4 friction layer samples of brake pad were determined according to the proposed method.The results showed that the relative standard deviations(RSD,n=6)of determination results of free phenol were less than 3％.5.0,10.0 and 30.0 mg/L of phenol standard working solution was added into sample for recovery tests.The recoveries were between 86％and 107％.
gas chromatographycapillary columnbrake padfriction layerfree phenol
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