De or het massaspectrum?

The correct Dutch article is:

het massaspectrum

Rule Words ending in -um and -ium: usually het. See the rule

How to use massaspectrum

the massaspectrumhet massaspectrum
this massaspectrumdit massaspectrum
that massaspectrumdat massaspectrum
our massaspectrumons massaspectrum
your massaspectrumjouw massaspectrum
every massaspectrumelk massaspectrum
which massaspectrum?welk massaspectrum?
a big massaspectrum / the big massaspectrumeen groot massaspectrum, het grote massaspectrum