No, the business may not retain your personally paid for equipment simply because you left that equipment at work. The fact that property is used in the course of your employment, loaned to another worker, or left at the place of employment does not give the employer any rights in or to it. If the employer does not return it, you could try contacting the police and reporting this as a theft; but if they will not help you, deeming this a "civil" matter, your recourse would be to sue the employer for the equipment's return or (if it was lost, disposed of, broken, etc.) its value. You should come armed with receipts showing that you purchased it and the price you paid.