Thermo Fisher Scientific Inc. (TMO) extended its $2.1 billion offer to acquire laboratory-equipment maker Dionex Corp. (DNEX) by a month after a tepid response to its tender offer.

As of 5 p.m. EST Thursday, just 20% of Dionex shares had been tendered to the offer. Thermo Fisher is offering $118.50 a share for Dionex, in a move to expand the company's presence in markets like environmental analysis, water testing and food safety.

The planned acquisition of Dionex, now expected to close later in the first quarter, would extend Thermo Fisher's offerings in liquid chromatography, a method of analyzing chemical substances.

Thermo Fisher sells its products--ranging from analytical instruments to lab equipment and services--to labs and research operations. The company's profit has improved lately as the company has seen better sales and improved margins.

Thermo Fisher in October reported that its third-quarter profit rose 21% as sales and margins strengthened.

Shares of Thermo Fisher and Dionex closed Thursday at $56.54 and $118.02, respectively. Dionex shares are up 64% since the December offer.

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