Classification of hyphenated instruments like GC-MS typically follows the principal function. If the chromatographic separation is the defining commercial feature and the MS serves as the detector, 87442 may apply; if the mass spectrometer is the primary analytical component and the GC is ancillary, the spectrometer heading (87443) could govern. Because this is a recurring classification dispute, a binding ruling from CBP is the most reliable path to certainty.

CBP may request the commercial invoice, packing list, and any licensing or software agreements bundled with the instrument, since software and installation services can affect dutiable value. For instruments with embedded proprietary software, importers should be prepared to demonstrate whether the software value is separately invoiced or included in the instrument price, as this affects the customs value calculation.