The presence of arsenic in drinking water is both a national as well as a global concern due to the lack of field equipment capable of verifying compliance with EPA and WHO arsenic safety guidelines. Arsenic is a natural element found in the earth's crust and, when ingested chronically, results in vomiting, esophageal and abdominal pain, and diarrhea. Arsenic is also a proven carcinogen and has been linked to the onset of cancer of the skin, lungs, urinary bladder, and kidneys. Objective: Implant Sciences proposes to investigate a novel, two-stage technique for selectively ionizing arsenic in solution. When coupled with an ion mobility spectrometer, this technique would offer high ionization specificity and efficiency and is expected to result in a method of measuring arsenic in drinking water at concentrations as low as a few parts per trillion. The information obtained in this study would be used to manufacture a rugged and portable field device for quantifying drinking water compliance with EPA and WHO guidelines. Specific Aims: The specific goal of this phase I investigation is to investigate the feasibility of using a two stage ionization method to allow for the measurement of arsenic in water. A secondary goal of this project would be to prove that this two-stage technique would offer arsenic detection capabilities better than 100 ppt, with a desired target sensitivity of 1 ppt. To achieve this goal, an electrospray liquid conversion module will be built and tested for compatibility with a novel laser-enhanced ionization IMS system developed internally at Implant Sciences Corporation. Aqueous arsenic standards will be generated and used for the purposes of this investigation. The proposed IMS system will use these standards to initially identify the arsenic signal at the IMS output. Once the arsenic signal is identified, parameters such as the drift gas, gas pressure, laser energy and density, electrospray voltage and drift tube potential will be optimized to achieve ppt arsenic sensitivity.