# Atomic Spectroscopy-Based Analysis of Heavy Metals in Seaweed Species
## 2 Atomic Spectroscopy-Based Heavy Metal Analysis Methods for Seaweed
### Sample Preparation  
Proper selection and treatment of seaweed samples are crucial since the complexity and homogeneity of a sample will dictate the subsequent steps that are needed to ensure accurate analysis. The use of titanium or high-purity glass knives and mixing blades and polyethylene and polypropylene containers along with the adoption of good laboratory practices can minimize trace element contamination. Containers made of quartz of borosilicate glass are less desirable. During sample preparation, glassware can be silanized to minimize the likelihood of contamination [45]. Conceivable sources of contamination include but are not limited to the analyst's skin, clothing, and gloves; sample containers; and metallic heating blocks and furnaces. Samples are commonly introduced into atomic spectrometers as solutions. Several procedures can be used to obtain seaweed samples in solution. The choice of digestion method is made upon considering the efficiency of sample decomposition, the level of contamination of samples, possible reagent-related interferences and matrix effects, the instrument and detection limit requirements, and safety aspects. Sample mineralization by an acid or a mixture of acids (wet ashing) on a heating plate under ambient pressure in a pressurized digestion vessel (digestion bomb) with open- and closed-vessel MW-assisted digestion or with ultrasound (US)-assisted extraction are among the most common sample preparations in food metal analysis. HNO\({}_{3}\) is the most suitable acid for spectrometric analysis since no significant analytical problems or minimal interferences are observed when it is used at concentrations up to10%. Due to the low oxidation potential of nitric acid, for optimum digestion, some materials require the addition of other types of acids despite the problems related to their use at high temperatures and pressures. To maintain a higher temperature under certain pressure limits and reduce the carbon contents in the digestates, often H\({}_{2}\)O\({}_{2}\) is added to mineralization samples without introducing any major analytical difficulties. Nevertheless, H\({}_{2}\)O\({}_{2}\)'s impurities limit the determination of some elements at low levels. Moreover, the use of HCl for GFAAS sample preparation may be challenging due to the formation of volatile and indissociable analyte chlorides that will lead to interferences. It is recommended to avoid the use of H\({}_{2}\)SO\({}_{4}\) (due to its high viscosity) in sample preparation procedures for analytical instruments that use nebulizers for sample introduction. In addition, H\({}_{2}\)SO\({}_{4}\) can sparingly form soluble sulfates that can precipitate from solution. Small amounts of other strong acids can be added for special analytical purposes, such as the addition of HF for the solubilization of Si-bound elements in food samples containing high amounts of Si [46]. Although HClO\({}_{4}\) and H\({}_{2}\)SO\({}_{4}\) are also used as oxidants, their production of a number of spectral interferences and their being potential sources of contamination and increased danger do not make them good choices for digesting agents. Open-vessel wet ashing digestion procedures for the determination of metals suffer from disadvantages, such as being time-consuming, the high possibility of analyte contamination and loss, and their not being vigorous enough for the complete mineralization of some matrices. To overcome these drawbacks, high-temperature and/or high-pressure methods are considered as alternative digestion methods. Microwave (MW)-assisted sample digestion is reported as a widespread technology in the field of food sample preparation [47]. Most often, small amounts of food samples are digested with HNO\({}_{3}\); a mixture of HNO\({}_{3}\) and HClO\({}_{4}\); or a mixture of H\({}_{2}\)O\({}_{2}\), HNO\({}_{3}\), and HClO\({}_{4}\). In the MW heating process, the energy is generated within the digestion mixture and not transferred by conduction (as with hot plates), leading to a more effective heating.