Observations of H _ { 2 } spectra in the line-of-sight of distant quasars may reveal a variation of the proton-electron mass ratio \mu = m _ { p } / m _ { e } at high redshift , typically for z > 2 .
Currently four high-quality systems ( Q 0347 - 383 , Q 0405 - 443 , Q 0528 - 250 and J 2123 - 005 ) have been analyzed returning a constraint \Delta \mu / \mu < 1 \times 10 ^ { -5 } .
We present data and a \mu -variation analysis of another system , Q 2348 - 011 at redshift z _ { abs } = 2.42 , delivering \Delta \mu / \mu = ( -1.5 \pm 1.6 ) \times 10 ^ { -5 } .
In addition to observational data the status of the laboratory measurements is reviewed .
The future possibilities of deriving a competitive constraint on \Delta \mu / \mu from the known high-redshift H _ { 2 } absorbers is investigated , resulting in the identification of a number of potentially useful systems for detecting \mu -variation .