Consumption of seafood has been on a steady rise based on reports of associated health benefits. Marine organisms are sources of staple and functional food. However, they are also the main source of total arsenic exposure in humans. Most food safety regulations are based on total arsenic. Unfortunately, total arsenic as an indicator for risk from dietary intake is inadequate. Knowledge of arsenic speciation is important as the chemical form of arsenic controls its bioavailability, mobility, and toxicity. Therefore, an accurate account for the myriads of arsenic species, naturally occurring in seafood, is required. However, this present considerable analytical challenge. Arsenic speciation in seafood is challenging owing to its existence in diverse chemical forms and oxidation states, interconversions between chemical forms, matrix complexity, lack of widely accepted analytical methods, and lack of commercially available standards and certified reference materials. Identification and quantification of the toxic arsenic species is imperative to understanding the risk associated with exposure to arsenic from dietary intake, which in turn underscores the need for speciation analysis. Setting of standards for arsenic in food is complicated, owing to the enormous metabolic diversity of organic arsenic species in humans, lack of knowledge about their toxicity, and lack of reliable speciation data on seafood. To establish human exposure to arsenic from seafood, five proxy seafood samples were selected to represent the entire food chain. The selection was based on their high consumption rate, which makes them economically important and a significant route for arsenic exposure. The seafood samples are either candidate reference materials or materials meant for interlaboratory comparisons, which require measurements for certification purposes or property values assignment. This work contributed towards that effort. Analytical methods for the determination of total arsenic and hydrophilic arsenic species were developed and optimized for analysis of the seafood samples. A structural library was developed based on in silico fragmentation data of extant lipophilic arsenicals that are reported in literature. The library aims to enhance the screening and identification of the novel lipophilic arsenicals for which very little is known, standards are not available, and whose toxicological profiles are of interest.