| CPC G01N 30/463 (2013.01) [G01N 30/16 (2013.01); G01N 30/88 (2013.01); G01N 2030/025 (2013.01)] | 20 Claims |

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1. A multi-dimensional gas chromatograph for analyzing compounds in a sample during a single run, the chromatograph comprising:
a first column;
a second column; and
a modulator disposed between the first column and the second column, the modulator modulating with (i) a first modulation period over a first time period during the run and (ii) a second modulation period over a second time period during the run later than the first time period, the second modulation period varying over the second time period.
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