Sharp gradients of chemical distributions in the nutricline are poorly resolved via conventional sampling techniques. Resolution of the fine structure of chemical distributions in the water column requires the use of in situ procedures. We describe here a high-resolution method for the measurement of nitrite concentrations in the upper 200m of the water column. A long-pathlength Teflon AF-2400 liquid core waveguide provides the low nanomolar detection limits required for observations of nitrite in near-surface waters. Our spectrophotometric elemental analysis system (SEAS) has a two second sampling period. Coupled with an 11cm/s descent rate, SEAS is able to accurately identify the depth of the primary nitrite maximum and provide a detailed inventory for nitrite in the upper ocean.