Is remote measurement of isotope ratios possible, or must a sample be aquired Is it possible to measure to measure isotopic abundance of remote astronomical objects - ie measurement without having a sample to feed into a mass spectrometer? Do different isotopes show any differences in absorption or emission spectra which can be used for this purpose?
Yes, isotopic ratios can be readily established by spectroscopy.

Molecules where the constituent atoms differ by one mass unit have different vibrational and rotational energy levels and the gaps between them depend on the reduced mass of the molecule. 

For example, in a diatomic molecule
$$ \mu = \frac{m_1 m_2}{m_1 + m_2}$$
and the vibrational frequencies depend on $\mu^{-1/2}$.

This technique is used for example to look at carbon monoxide feature in the infrared and establish the ratio of $^{13}$C/$^{12}$C.

The isotopic shift for atoms is much smaller in general, but is still detectable. The different mass of the nucleus changes the reduced mass of the electron (a little) and this changes the wavelength of the characteristic transition. 

An interesting example of this has been the search for $^6$Li in the spectra of population II stars (e.g. Asplund et al. 2006). This isotope of Li should be produced in the big bang along with the more common $^7$Li but is more readily burned in stellar interiors.

The main optical resonance line of lithium occurs at 670.8 nm. The difference between the  wavelength of this line (actually, it is an unresolved doublet) is 0.015nm. This separation cannot be resolved in stellar spectra and instead the shape of the absorption line has to be modelled to estimate the $^6$Li/$^7$Li ratio.

The isotopic shifts become smaller for heavier elements.