Alton Plans to Buy Source Scientific

Alton Group Inc., which makes medical instruments, said Wednesday that it has signed a letter of intent to buy Source Scientific Systems Inc. of Garden Grove for $2.25 million.

Alton, based in Irvine, manufactures analytical instruments--including a blood oxygen monitor used during open-heart surgery. Source Scientific, a unit of MicroProbe Corp. in Bothell, Wash., makes laboratory testing equipment.