Capillary Electrophoresis (CE)

1. CE Instrumentation Setup

1. Turn on the CE instrument and computer. Using the computer software, turn on the light source for UV analysis to allow it to warm up. Some software has an indicator when the lamp is ready for use (lamp icon turns color).
2. Make a methods file. Set the important parameters for running the CE. In this analysis the temperatures of the cartridge and sample storage are 35 °C. The wavelength for UV detection is 214 nm.
3. Write a time program. The program generally consists of rinse steps (to clean the capillary before analysis), injection steps, and then an electrophoresis step. For the rinse step, perform 2 rinses for 1 min using 20 psi of pressure. The first rinse is with NaOH, which helps make sure the silanol groups on the capillary wall are deprotonated. The second rinse is with run buffer (0.025 M borate buffer here) to make sure the capillary is left equilibrated with buffer.
4. For the injection, pressure injection is used at 0.5 psi for 5 s.
5. For the electrophoresis step, the conditions are separation voltage: 20 kV, time: 5 min, normal polarity. For each step, also indicate which vial is the inlet and which vial is the outlet. Save the methods file after all the parameters are entered.

2. Preparation of the Standards and Soda Samples

1. Make 500-ppm stock solutions of aspartame, caffeine, and benzoic acid in water. Make 50 mL of each, using a volumetric flask.
2. Make a standard solution of 150 ppm aspartame, 150 ppm caffeine, and 100 ppm benzoic acid in a 10-mL volumetric flask.
3. Make standard caffeine solutions of 50 ppm, 100 ppm, 150 ppm, and 200 ppm in a 10-mL volumetric flasks.

3. Run the Samples on the CE

1. Place the vials containing either standards or soda samples into the sample vial holder. Make sure to write down which sample is in which slot. Two slots have the borate run buffer and the 0.1 M NaOH rinse solution.
2. In the method file, input which slot the first sample vial is in.
3. Acquire a single run, making sure to input all the data information the program requests.
4. Continue to acquire data, changing the input vial for each sample. Run the combination standard, the 3 concentrations of caffeine, and a Pepsi and diet Pepsi sample.
5. Insert the target into the instrument and choose the appropriate instrument.
6. Analyze the data on the computer. Calculate the peak areas and overlay standards and real samples to help identify peaks. Make a calibration curve for the caffeine data.