Use of the same buffer over the course of a set of samples will result in a phenomenon known as buffer depletion. Ions move through the capillary due to the high voltage applied during electrophoresis. Positive ions will gather to the negatively charged electrode and negative ions will collect at the positively charged electrode during the course of electrophoresis. This ion movement results in an imbalance referred to as buffer depletion. To correct this imbalance, the buffer is replenished or replaced on a regular basis. The buffer needs to be changed every day or two if the instrument is being used to its full capacity.
If the buffer is not replenished frequently, the DNA fragments will not separate as well due to ion depletion effects. The current will drop when the buffer becomes too depleted. For example if the normal run current with a fresh buffer is 8 ||A at 15 000 V then it will drop to 4—5 ||A when the buffer becomes depleted. The current can thus serve as a useful diagnostic.
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