What component of an HPLC introduces an aliquot of sample into the column and how is this introduction accomplished with the high pressure in the flow path?
a. A syringe is used with a flexible tip placed into the flow path.
b. A flame ionizes the sample and sprays it into the column.
c. A flexible septum is coated with sample and placed in the column.
d. A fixed-loop injector with a switching valve moves the sample into the flow path.