A method for the determination of inorganic arsenic (iAs) without chromatography using hydride generation — inductively coupled plasma mass spectrometry (HG-ICPMS) is applied to 40 brown macroalgae samples (Fucus vesiculosus, Ascophyllum nodosum, Saccharina latissima). Determining iAs in seaweed matrices is a challenge and, in this study, using 2% HNO3 and 3% H2O2 extraction media the HG-ICPMS outperformed the most commonly used method of HPLC-ICPMS for the determination of iAs in the seaweed samples. There was a good comparison between the simple and fast HG-ICPMS and the more accurate but time-consuming HPLC-HG-ICPMS. Linear regression showed reasonable linearity (R2 of 0.82), with a slope slightly higher than 1 (1.15 ± 0.09) and intercept 0.03 ± 0.01 when comparing the concentrations of iAs determined with the two methods. Hence there is a minor overestimation of iAs with HG compared to the HPLC-HG, however, the method is well suited as a quick screening method. The iAs concentration was below 1% of total arsenic concentration for all the seaweed samples irrespective of using HG-ICPMS or HPLC-HG-ICPMS.