TOC analyzer: Elementar Vario Select, Germany.

check out the following publication for advantages and drawbacks of different methods: http://link.springer.com/article/10.1007/s11368-013-0715-1 (and included references). I can recommand all Elementar products as well (we are about to buy a Vario EL for our lab), but the do not offer multi-stage temperature combustion.

Have you ever worked with Rock-Eval? It's an expensive but high performance instrument for TOC analysis. Then you can use Intelligent method to accelerate your research.

From best methods is UV/Persulfate oxidation method and I prefer those instruments with conductivity cells as detector. You still need the high temperature method for higher concentrations, so it depends on your samples concentrations ranges.

At HCWW we use the first method accurately till 50 ppm max.