Assessment of selected heavy metals in honey samples using flame atomic absorption spectroscopy (FAAS)

Analytical procedures to heavy metal analysis

Honey samples were heated at 65oc on a water bath until liquefy to allow easier handling and have more uniform distribution [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]. The samples were then cool and weigh for the next analysis. 12 mL of an acid mixture (3:1 ratio of HNO3 and H2O2) were added in 100 ml conical flask containing 1 g of honey. The flasks were heated on the hot plate until the manufacturing of red NO2 gases ceases. The content was evaporated, the quantity became decrease to about 3–5 ml but not too dry. After cooling the flask 10 ml of distilled water was added and the solution filtered through the Watmen Number 1 filter paper and transfers to a 25 ml flask. It was then made up to fill with deionized water. Next to this 10 mg/L intermediate standard solution is used to prepare the working solution of the metals (Pb, Cd, Zn, Cu, Mn, and Cr) from 1000 mg/L stock solution and to dilute with 50ml distilled water. Finally, the metals have been determined by atomic absorption spectrophotometer (AAS). Each standard concentration and absorption became used to prepare a curve. The metal concentrations were calculated from the standard curve [627].

Apparatus and equipment

The laboratory devices that were used for this study include: digital Analytical Balance (Model CTG1200-1200), refrigerator (Model No.LR.1602 England), hot plate, water bath, volumetric flasks, beakers, measuring cylinders, spatula, funnel, filter papers, pipettes and micropipettes, round bottom flask and Atomic Absorption Spectrometer (BUCK SCIENTIFIC MODEL 210VGP).

Chemicals and reagents

Reagents that were used in the analysis were HNO3, HCIO4 and H2O2 were used for decomopstion of honey samples. And also used during optimization of honey samples. Stock standard solutions (1000 mg/L) containing the metals Pb, Zn, Cu, Cd, Mn, and Cr metals were used for the preparation of calibration standards and in the spiking experiments. Deionized water was used all over the experiment for sample preparation, dilution and cleaning apparatus.

Calibration of the instrument

The instrument was calibrated using six-seven series of working standards. The working standard solutions of each metal were prepared by diluting the intermediate standard solution. The working standard, the intimidate standard and the value of the correlation coefficient of the Calibration for each heavy metal was shown in (Table 1).

No Metal Intermediate

Standards (mg/L)

Working standards


Correlation coefficient of calibration curves
1 Cu 10 0.02,0.5,1,1.5,2,2.5,3 R2 = 0.996
2 Zn 10 0.02,0.5,1,1.5,2,2.5,3 R2 = 0.991
3 Pb 10 0.01,0.2,0.4, R2 = 0.993
4 Cd 10 0.001,0.2,0.4,0.6,0.8,1 R2 = 0.996
5 Mn 10 0.02,0.5,1,1.5,2,2.5,3 R2 = 0.996
6 Cr 10 0.01,0.5,1,1.5,2,2.5,3 R2 = 0.992


Data analysis

The experiments were conducted in triplicate. Data were calculated as mean± standard deviation (SD) and were performed using SPSS version 20. Some tests such as one-way ANOVA were used for data analyzing.

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