title: Analysis of trace levels of domoic acid in seawater and plankton by liquid chromatography without derivatization, using UV or mass spectrometry detection.
abstract: Quantitation of trace levels of domoic acid (DA) in seawater samples usually requires labour-intensive protocols involving chemical derivatization with 9-fluorenylmethylchloroformate and liquid chromatography with fluorescence detection (FMOC-LC-FLD). Procedures based on LC-MS have been published, but time-consuming and costly solid-phase extraction pre-concentration steps are required to achieve suitable detection limits. This paper describes an alternative, simple and inexpensive LC method with ultraviolet detection (LC-UVD) for the routine analysis of trace levels of DA in seawater without the use of sample pre-concentration or derivatization steps. Qualitative confirmation of DA identity in dubious samples can be achieved by mass spectrometry (LC-MS) using the same chromatographic conditions. Addition of an ion-pairing/acidifying agent (0.15% trifluoroacetic acid) to sample extracts and the use of a gradient elution permitted the direct analysis of large sample volumes (100 microl), resulting in both high selectivity and sensitivity (limit of detection=42 pg ml(-1) by LC-UVD and 15 pg ml(-1) by LC-MS). Same-day precision varied between 0.4 and 5%, depending on the detection method and DA concentration. Mean recoveries of spiked DA in seawater by LC-UVD were 98.8% at 0.1-10 ng ml(-1) and 99.8% at 50-1000 ng ml(-1). LC-UVD exhibited strong correlation with FMOC-LC-FLD during inter-laboratory analysis of Pseudo-nitzschia multiseries cultures containing 60-2000 ng DA ml(-1) (r(2)>0.99), but more variable results were obtained by LC-MS (r(2)=0.85). This new technique was used to confirm the presence of trace DA levels in low-toxicity Pseudo-nitzschia spp. isolates (0.2-1.6 ng ml(-1)) and in whole-water field samples (0.3-5.8 ng ml(-1)), even in the absence of detectable Pseudo-nitzschia spp. cells in the water column.
authors: National Research Council, Institute for Marine Biosciences, Halifax NS B3H 3Z1, Canada.
authors: Luiz L
authors: LL
authors: Mafra
authors: Claude
authors: C
authors: Léger
authors: Stephen S
authors: SS
authors: Bates
authors: Michael A
authors: MA
authors: Quilliam
mesh_terms: D000818:Animals; D002853:Chromatography, Liquid / Q000379:methods*; D017377:Diatoms / Q000737:chemistry; D007608:Kainic Acid / Q000031:analogs & derivatives* / Q000032:analysis; D016014:Linear Models; D013058:Mass Spectrometry / Q000379:methods*; D010839:Phytoplankton / Q000737:chemistry*; D015203:Reproducibility of Results; D012623:Seawater / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013056:Spectrophotometry, Ultraviolet / Q000379:methods*
chemical_list: C012301:domoic acid; D007608:Kainic Acid