Complex sentence: However, the direct method is far less practical than the indirect method, and is not commonly used in laboratories, since the primary antibodies must be covalently labeled, which require an abundant supply of purified antibody.
Split into simpler sentences: However, the direct method is far less practical than the indirect method. The direct method is not commonly used in laboratories since the primary antibodies must be covalently labeled and this can require an abundant supply of purified antibody.