Vaporization-collection in-line preconcentration (VCIP) is proposed for simple and highly sensitive measurement of vaporizable water pollutants. In this work, VCIP has been applied to arsenic analysis to develop an instrument for use in the field. The signal is 200 times higher than with conventional direct injection. Low ppb levels of As can be analyzed automatically in one step. This method is expected to be applicable to the measurement of very low levels of other water vaporizable pollutants as well.