# Atomic Spectroscopy-Based Analysis of Heavy Metals in Seaweed Species
## 2 Atomic Spectroscopy-Based Heavy Metal Analysis Methods for Seaweed
### Atomic Mass Spectrometry
The amounts and compositions of polysaccharides in the cell walls of the seaweeds; environmental factors, such as water temperature, pH, and salinity; the relative abundances of the elements in seawater; as well as the presence of other metals were hypothesized to have caused these differences. The pressurized hot water extraction (PHWE) method was used to extract multiple trace metal elements (As, Cd, Cr, Mn, Ni, Pb, and Zn) from seven edible seaweed samples harvested from Northwestern Spain, and this was followed by ICP-MS analysis [17]. Several PHWE parameters (modifier concentration, extraction temperature, pressure, extraction steps, etc.) were evaluated and optimized. The optimal condition was found to be with 150 mM acetic acid, at an extraction temperature of 130 \({}^{\circ}\)C and a pressure of 3000 psi, for a static time of 5 min and three cycles. The resulting extract was measured on an \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Northwestern** & **Gulf of** & & **Coast of the** & \\  & **Spain [17]** & **Thessaloniki,** & **Sean Sea [19]** & **South Korea [60]** & **Southeast Asia [7]** & **Northwestern** & **Greenland [24]** \\ \hline Cd & 0.86 & 0.016–1.121 & 0.038–0.119 & 0.234–7.33 & 0.62–0.54 & 0.134–2.96 \\ \hline Sn & & & 0.004–0.947 & 0.043–4.6 & \\ \hline Sb & & & 0.002–0.313 & 0.045–1.1 & \\ \hline Hg & & \textless{DL} *-0.006 & 0.005–0.068 & 0.010–0.12 & \textless{0.078} \\ \hline Tl & & & 0.0004–0.02 & 0.010–0.13 & \\ \hline Pb & 0.02 & 2.697–27.94 & 0.032–0.988 & 0.141–28.40 & 2.2–40 & 0.101–1.59 \\ \hline U & & 0.037–1.542 & & 0.015–1.260 & \\ \hline \hline \end{tabular}
* DL stands for “detection limit”.  
\end{table} 
Table 4: _Cont._ICP-MS instrument in standard mode. Based on the optimized modifier concentration, ICP-MS calibration was performed with 150 mM acetic acid aqueous standard solutions. The seaweed samples were also subjected to the standard extraction method of microwave-assisted acid digestion to assess the total metal contents as well as for comparison with the PHWE method. Validation was performed with a CRM which has certified values for As, Cd, Pb, and Zn. Analysis data for some of the other elements (Cr, Mn, and Ni) were compared with data reported in the literature, and similar values were found. The authors concluded that PHWE serves as a fast, simple, \"green\", and effective method to extract metal elements from seaweed. Edible seaweed from South Korea (five species) were analyzed for levels of toxic heavy metals (As, Cd, Hg, and Pb), among which As, Cd, and Pb, as well as various As species, were measured with ICP-MS in standard mode [92]. Quantities of 0.25-0.5 g of the seaweed samples were subjected to the microwave-assisted acid digestion procedure using HNO\({}_{3}\):H\({}_{2}\)O\({}_{2}\) (7:2 \(v/v\)) in PTFE digestion vessels. The As species were extracted with 50% methanol in 1% HNO\({}_{3}\) and separated with liquid chromatography prior to quantification on an ICP-MS instrument, allowing for the determination of individual As species, including the more toxic inorganic species, such as As(III) and As(V). Calibration was performed at eight different concentration points to ensure linearity over the data range. Blanks and calibration standards were analyzed at regular intervals to check for instrumental drift and cross-contamination. Method validation was performed with a CRM. Spike recovery for all of the elements analyzed and the As species was between 94.5 and 107%, thus verifying the described method as efficient and accurate for monitoring toxic heavy metals in edible seaweed. Since the concentrations of all four toxic heavy metals were found to be lower than the recommended PTWIs (provisional tolerable weekly intakes), the authors concluded that these five species of edible seaweed are safe to consume. Ninety-two samples belonging to three species of edible seaweed from Southeast Asia were analyzed for 19 trace elements (As, Cd, Co, Cr, Cu, Fe, Hg, Mo, Mn, Ni, Pb, Sb, Se, Sn, Sr, TI, U, V, and Zn) with ICP-MS [7].