Context : In previous papers , we introduced our method for measuring chemical abundances from integrated-light spectra of globular clusters and applied it to a variety of extragalactic star clusters .
Our work so far , however , has concentrated primarily on the optical range 4200 Å– 6200 Å .

Aims : Here we extend our analysis technique to the infrared and test it on an H -band spectrum of the massive globular cluster G280 in M31 .

Methods : We simultaneously analyse an optical spectrum of G280 , obtained with the HIRES spectrograph on the Keck I telescope , and an H -band spectrum obtained with NIRSPEC on Keck II .
We discuss the sensitivity of our results to various modifications of the input assumptions , such as different line lists and isochrones and the possible presence of a metallicity spread in G280 .

Results : When using the most recent version of the Kurucz line list , we measure iron abundances of \mathrm { [ Fe / H ] } = -0.68 \pm 0.02 from the optical spectrum and \mathrm { [ Fe / H ] } = -0.60 \pm 0.07 from the infrared spectrum .
These values agree well with previous spectroscopic determinations of the metallicity of G280 .
While the small difference between the optical and infrared measurements is insignificant given the uncertainties , it is also consistent with a metallicity spread similar to that observed in massive GCs such as \omega Cen and G1 , and also hinted at by the colour-magnitude diagram of G280 .
The optical and infrared spectra both indicate an \alpha -enhancement of about 0.3–0.4 dex relative to solar-scaled abundances , as typically also observed in Milky Way GCs .

Conclusions : From this analysis , it appears that our integrated-light analysis technique also performs well in the H -band .
However , complications due to the presence of molecular bands and telluric contamination are more severe in the infrared , and accurate modelling of the coolest giants is more critical .