A　simple,　rapid　and　sensitive　method　for　determination　of　trace　levels　of　domoic　acid　(DA)　in　seawater　was　developed,　based　on　a　magnetic　solid-phase　extraction　(MSPE)　followed　by　high-performance　liquid　chromatography　with　tandem　mass　spectrometry　(HPLC-MS/MS).　Five　kinds　of　ferrite　magnetic　nanospheres　(MFe2O4;　M　=　Fe,　Co,　Ni,　Cu　and　Zn)　were　prepared　and　first　used　as　sorbents　for　MSPE　of　DA　and　removal　of　salt　interference.　Under　the　same　extraction　and　elution　conditions,　CuFe2O4　magnetic　nanospheres　provided　the　best　pretreatment　performance,　which　were　then　characterized　in　detail.　After　further　optimization　of　conditions,　the　developed　method　showed　good　linearity　(r(2)　=　0.9991)　with　the　range　of　5-1000　pg　mL(-1),　low　limit　of　detection　(2.5　pg　mL(-1);　SiN　=3:1),　low　limit　of　quantification　(5.0　pg　mL(-1);　S/N　=　10:1),　and　good　recoveries　(86.0-98.1%)　with　acceptable　repeatability　(RSD　＜=　6.5%;　n　=3)　in　seawater　samples.　The　results　demonstrated　that　the　ferrite　magnetic　nanospheres　are　promising　sorbents　for　efficient　extraction　of　highly　polar　analytes　from　high　ionic　strength　solutions.　(C)　2016　Elsevier　B.V.　All　rights　reserved.