A new desorber design for use in the couloximetric determination of oxygen in water samples is described. In comparison with previous systems it significantly improves the efficiency of transfer of oxygen from sample to carrier gas and reduces the ingress of atmospheric oxygen through leaks. Lower and more stable baselines are now attainable, with levels of <0.5 μV being commonly produced. The enhanced stability of the baseline has decreased the lower limit of oxygen detection to around 0.13 pg of oxygen. The minimum sample size for analysis with a 1% error due to baseline fluctuation has also been reduced to around 1 μl for saturated seawater at 0°C.