Determination of BPA in thermal paper

BPA (PBA) is one of the color developers commonly used in heat-sensitive coatings. BPA substances have certain toxicity to the human body, and the BPA in thermal paper will dissolve with sweat and increase with the prolongation of contact time. Therefore, it is necessary to detect and monitor BPA.

1. Materials and methods
1.1 Materials and Instruments

1.1.1 Instruments and equipment

Shimadzu LC-20A high-efficiency liquid chromatograph: equipped with binary high-pressure pump, fluorescence detector, SIL-20A autosampler, column thermostat, and chromatographic data workstation.

Water bath, shaker.

1.1.2 Reagents

Acetonitrile, methanol: chromatographically pure; ultrapure water (Millipore, resistivity 18.2MΩ/cm).

1.1.3 Standards

BPA (Biaphenol A): 100mg/L.

1.2 Experimental method

1.2.1 Preparation of standard products

Take 1 mL of BPA standard solution into a 100 mL brown volumetric flask, and dilute to the mark with acetonitrile to prepare a standard stock solution with a concentration of 1 mg/L.

1.2.2 Sample pretreatment

Cut out a 2.5cm×2.5cm square piece of heat-sensitive paper, cut it into pieces with scissors, and place it in a 50mL test tube. Add about 25mL of methanol and place in a 60°C water bath for 1h. After taking it out, shake it on a rotary shaker for 30 minutes, let it stand, cool to room temperature, and dilute to 25mL with methanol. Pass through a 0.2μm syringe filter (nylon), and the filtrate is used for high performance liquid chromatography analysis.

2. Results and discussion
2.1 Sample pretreatment conditions

When methanol is used as the extraction solvent, the recovery rate is between 96-101%.

2.2 Selection of mobile phase

The methanol-water system has a good separation effect between the target and impurities, and the best effect is when the ratio is 70:30.

2.3 Linear relationship and detection limit

The minimum detection limit of this method is 0.02μg/cm2.

2.3 Recovery and precision of the method

The recovery rate of this method is between 96.0-101.2 percent; the relative standard deviation is within 2.01 percent, which can fully meet the requirements of the test for accuracy and precision.

3. Conclusion
The pre-measurement treatment of the method is simple, and the process loss is less. The peak shape is good, the result is accurate and reliable, the recovery rate of BPA is between 96.0-101.2%, the relative standard deviation is within 2.01%, and the detection limit is 0.02μg/cm2, which can meet the requirements of thermosensitive Requirements for the detection of BPA in paper.