# Atomic Spectroscopy-Based Analysis of Heavy Metals in Seaweed Species
## 2 Atomic Spectroscopy-Based Heavy Metal Analysis Methods for Seaweed
### Atomic Absorption Spectrometry (AAS) Techniques
#### 2.2.1 Flame Atomic Absorption Spectrometry  
Flame atomic absorption spectrometry (FAAS), where a flame is used to atomize the elements, is widely accepted in many industries, which continue to utilize the unique and specific benefits of this technology. FAAS is simple, robust, and inexpensive for analysis of a wide range of elements. On account of the maturity of the technique, relatively well-established FAAS methods are available in the analytical literature. Calibration with aqueous standards can typically be accomplished using 3- to 5-point calibration curves. Conversely, FAAS has the limitation of transient and relatively diffuse atom density in the flame, which results in poor sensitivity when compared to other techniques. Typical detection limits are in the high ppb to ppm range [53; 54]. Thermospray flame furnace atomic absorption spectrometry (TS-FF/AAS), as a relatively new technique, considerably increases the sample-introduction efficiency compared to traditional settings. The increased residence time of the sample in the flame results in better sensitivity, which can improve the DLs for a number of elements [55]. Among the elements of interest in the food industry, selenium (Se) measurement by traditional FAAS suffers from a relatively poor detection limit (DL) of around 1 ug/mL; however, the application of hydride generation (HG) sample introduction lowers the DLs to sub-parts per billion for Se [56]. Several examples of heavy metal analysis in seaweeds using AAS are given in the following sections, and the measured concentrations are presented in Table 2.  
[PERSON] et al. analyzed green, brown, and red seaweed species from different intertidal regions of the Persian Gulf and the Gulf of Oman for the determination of Cu, Zn, Pb, Ni, Fe, and Cd concentrations [57]. Samples (1 g each) were digested in polytetrafluoroethylene  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline  & \begin{tabular}{c} **Persian Gulf** \\ **and the Gulf of** **Oman** [37] \\ \end{tabular}  & \begin{tabular}{c} **Southern** \\ **Thailand** \\ **Provines** [8] \\ \end{tabular}  & \begin{tabular}{c} **Bay of** \\ **Bengal** [34] \\ \end{tabular}  & \begin{tabular}{c} **Coastal Areas of** \\ **Rameswaram, Tamil** \\ **Nadu, India** [22] \\ \end{tabular}  & \begin{tabular}{c} **Coastline of** \\ **Homuzgan** \\ **Provinec, Iran** [18] \\ \end{tabular}  & \ \begin{tabular}{c} **Coastal Areas of** \\ **Karachi,** \\ **Arabian Sea** [40] \\ \end{tabular}  & \begin{tabular}{c} **Coastal Sites of** \\ **Northeast** \\ **England** [41] \\ \end{tabular}  \\ \hline Cr & 1.43–2.80 & ND * & & & 0.004–4 & 0.8–5.0 \\ \hline Mn & 557.05–746.75 & 0.543–3.615 & - & - & 0.006–1.57 & 18.8–778. digestion vessels with 5 mL concentrated HNO\({}_{3}\) at ambient temperature for 2 h followed by heating for 5 h at 100 \({}^{\circ}\)C until 1 mL of the acid remained. Filtered cool solutions were diluted to 50 mL in polypropylene volumetric tubes and analyzed. [PERSON] et al. 's method was used for blank preparation [58]. The results showed that Fe, Ni, Zn, Pb, Cu, and Cd were found in all the studied seaweed species. It was also found that the contamination levels in seaweeds were related to collection sites, seaweed species, and environmental factors, such as salinity, pH, and light intensity. Another research group used method 975.03 of AOAC 2000 to analyze heavy metal contents in warm-water seaweeds (_Gracilaria fisheri_) cultivated in Southern Thailand provinces [8; 59]. A quantity of 1 g of dried sample was soaked in 10 mL HNO\({}_{3}\) followed by the addition of 3 mL 60% HC1O\({}_{4}\). The mixture was heated slowly on a hot plate until frothing ceased and the HNO\({}_{3}\) had almost evaporated. After cooling, 10 mL HCI was added, mixture-filtered through a microfiber filter, and volume-adjusted to 50 mL prior to analysis. The researchers found that Mn and Fe were the main microelements in the studied seaweed species, while Ni and Pb were the dominant heavy metals.