The presence of domoic acid in aquatic species was reported for the first time in the United States in the late summer of 1991 in Monterey Bay, California. By October of 1991, domoic acid was found in razor clams (Siliqua patula) and in the viscera of Dungeness crab (Cancer magister) along the coasts of Washington and Oregon. In response to this outbreak, the National Marine Fisheries Service, in cooperation with the Washington State Department of Fisheries began analysis of Washington State razor clams for the period from November 1991 to June 1993. This survey indicated that domoic acid levels in the edible portion of the razor clams peaked in December of 1991 (average of all Washington state coastal sites: 106 ppm) and followed a slow decline to the present day low levels (< 5 ppm). Sixteen months after the maximum level, domoic acid has not completely disappeared from the razor clams from the Washington State beaches. Unlike mussels (Mytilus edulis), where the toxin is found only in the viscera, domoic acid distributes itself throughout the various body parts of the razor clam. The highest concentration occurs in the foot or "digger" and the lowest in the siphon or "neck." The concentration of domoic acid in the razor clam foot reached a high of 230 ppm.

Domoic acid (DA) was first reported in mussels from Prince Edward Island, Canada, in 1987. It reappeared in anchovies and pelicans from Monterey Bay, California, in 1991. Later that year, domoic acid was found in razor clams and Dungeness crabs along the Washington and Oregon coasts. Since the initial outbreak, a variety of analytical methods for the detection of this neurotoxin have been developed. Here, we describe a modification to the solid phase extraction (SPE) clean-up step in Quilliam's HPLC-UV method (1991: NRCC No. 33001). The standard 10% acetonitrile (MeCN) wash and 0.5M ammonium citrate buffer (ACB) in 10% MeCN (pH = 4.5) eluting solution have been replaced with a 0.1M sodium chloride (NaCl) in 10% MeCN wash and a 0.5M NaCl in 10% MeCN eluting solution. This modification allows the analysis to work equally well on both clam and crab viscera and meat. Chromatograms of visceral samples no longer contain interfering or late eluting peaks; and all chromatograms are free of the large solvent peak tailing associated with the ACB eluent. The newly modified method allows for an improved and more versatile domoic acid analysis.