hplc-ms can definitely be used with just a database since the ms fragmentation pattern is characteristic for a given compound. it's more accurate with some internal standard especially for quantification but there's typically a uv-vis absorption spectrometer module too so you can compare against the database ε as long as all the peaks are well separated and you can identify them from the ms. but the margin of error will be a lot higher than getting the offset of your analyte from a set of standards of known concentration.