Thermo Fisher Scientific Inc. (NYSE:TMO) today announced a deal to take over Sunnyvale Calif.-based Dionex Corp. (NSDQ:DNEX).

The Waltham, Mass.-based lab instruments maker plans to pay about $2.1 billion in cash for Dionex, or $118.50 per share, a 21 percent premium over DNEX’s last closing price of $98.16.

Dionex develops chromatography and extraction systems for separating and identifying the components of chemical mixtures, according to its website. The merger would fill out Thermo Fisher’s mass spectrometry offering, according to the company.

The boards of both companies have approved the transaction, which is expected to close in the first quarter of 2011, according to Thermo Fisher. In mid-afternoon trading, DNEX shares were going for about $118.00, up slightly more than 20 percent for the day.

Thermo Fisher announced plans to acquire Australian lab supplies provider Lomb Scientific for an undisclosed amount Dec. 1, in a bid to widen its footprint in Asia and the Middle East. The latest merger deal expands TMO’s footprint in China and other Asia-Pacific markets, where Dionex generates about 35 percent of its revenues, according to the company.

"[The acquisition] complements our strong presence in China, where we’ve established the headquarters for our global environmental instruments business and continue to build our commercial infrastructure to meet the needs of customers in growing water quality, consumer safety and life sciences markets,” said Thermo Fisher CEO  Marc Casper in prepared remarks.