Determination of Zinc Content in Commercial Toothpaste Samples in Nigeria by Atomic Absorption Spectrophotometric Method

Zinc as its citrate or sulphate salt is added to some toothpaste as a bactericide to reduce the presence of bacteria in the mouth. These bacteria can form plaque or produce acids which cause dental decay and halitosis. Zinc salt is added at amounts which are enough to show activity against oral bacteria without causing toxicity to the user. Five commercial samples of different brands of toothpaste (TP-A, TP-B, TP-C, TP-D and TP-E) were purchased from different pharmacy stores in Ogige and Eko markets, Nigeria and analysed for the presence of zinc using atomic absorption spectrophotometric method. The samples were digested with deionized water and HNO3, centrifuged and filtered. The absorbance of the supernatants obtained was read with a spectrophotometer. Calibration curves for zinc sulphate and zinc citrate were obtained with regression (R2) values of 0.9992 and 0.9973, respectively. The equation obtained from the curves used in determining the content of zinc in the samples. The zinc content (% w/w) of samples was determined to be 0.8467%, 0.8127%, 0.0119%, 0.0188% and 0.0305%, respectively. These values were well below the maximum permissible level of zinc in toothpaste samples but were within the upper limit for daily zinc intake.