Study area and sampling location: We collected ten indigenous fresh fruit species which are highly consumed by the Bangladeshi population from two different local markets Dhaka city, namely: Mirpur-10 and Mohammadpur Krisi Market.
Selection of Elements: The concentrations of four toxic elements Lead (Pb), Cadmium (Cd), Chromium (Cr), and Mercury (Hg) determined in 20 samples of commonly fresh fruit.
Collection and preservation of samples After collection fruit species have been wrapped in polythene bags to transport to the Analytical Chemistry Laboratory, Chemistry Division, Atomic Energy centre Dhaka, Bangladesh Atomic Energy Commission, immediately after transportation to the laboratory samples have been washed with distilled water, further washed with deionized water to remove the dirty or other fouling substances. The edible parts of each sample have been removed and chopped into pieces with the aid of a steam cleaned stainless steel knife, then took the weight of samples. After that, the samples are dried in 100°C ovens until the samples are dehydrated, which achieved by reaching constant pressure and temperature for 2 days. Then we took the weight of the dry sample to measure the moisture content of fruits. Further, the dried samples have been grounded into a fine powder form and stored in a fresh plastic polythene bag ready for digestion.
Sample digestion: To determine the trace elements from edible portions of the fruit acid digestion method has been performed. Acid digestion is a method of dissolving samples into solutions by adding acids and heating until the complete decomposition of the matrix. In this study, the acid digestion method executed by using a hot plate. In hot plate digestion system from each fruit sample, 1g dry sample placed in a 100 ml beaker. Afterward, about 8 ml of concentrated nitric acid (analytical grade, 65%) poured into the beaker. A crystal glass placed at the mouth of the beaker, and the beaker placed on a magnetic hot plate. The mixture has been heated for 2 hours to remove all oxidizable matter. Then 1 ml of hydrogen peroxide (30%) added in the mixture and the temperature maintained for another 30 minutes. Once the digestion has completed while all samples completely dissolved in the acid and the volume content is 1 ml. The digested acid solution filtered by filter paper and adding reduced to deionized water and stored in 25 ml vial.
Blank Preparation: During the digestion process of fruit samples, reagent blanks (laboratory blank) prepared to ensure that the samples and the chemicals used are not contaminated. They are arranged similarly as samples, except that no samples added to the digestion vessels. After digestion, reagent blanks are rated as samples and diluted with the same factor. They are analyzed before the main samples. Each set of digested samples have its reagent blanks and corrected by using their blank samples.
Spike Sample Preparations: Spike sample analysis used to test the method at varying concentrations of the analyte. Known amounts of analyte added to the unknown sample and calculated the recovery percent. If interferences are present in the samples, the results obtained are significantly higher or lower than the actual concentration. Each set of digested samples has at least one spike sample.
Instrumental Analysis: A Varian AA28OZ Atomic Absorption Spectrometer (AAS) with Zeeman background correction system equipped with a graphite furnace (GTA 120)and an autosampler (PSD120)used for the determination of Pb, Cd and Cr. Moreover, Hg determined using Cold Vapour AAS (CV-AAS).Atomic signals measured for Pd, Cd, Cr in peak area mood and Hg in integration mood. The working standard solutions prepared by appropriate dilution of the respective 1000 milligram per liter (mg/L)stock standard solutions using 1%(w/w) supra pure grade Nitric Acid (MerckDarmsta, Germany). All containers and glassware have been cleaned by soaking into 20% Nitric acid for at least 24 hours and rinsed three times with deionized water before use.
Statistical analysis Statistical analyses carried out by using Statistical Package for Social Science (SPSS) for Windows version 16.0. The results obtained in the present study are reported as mean values ± standard deviation (SD).