Inorganic analysis of food for metals that might be harmful to health is an important part of ensuring food safety. Metals can contaminate raw products through exposure to contaminated soil or water during growth. Contamination during transport is also possible. During processing, gross or trace contamination can be introduced through machinery used. Product packaging can contribute to the contamination and was the subject of a U.S. FDA import alert describing lollipop candies contaminated with lead from the packaging ink. Levels of metals permissible in food are not defined clearly in U.S. regulations, although some guidance has been developed through prior encounters with contaminated food (1).

This work compares techniques for metal measurement in a variety of foods using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and inductively coupled plasma-mass spectrometry (ICP-MS). The suitability of the techniques for analytical capability and productivity will be compared.

Experimental

Table I: Microwave digestion program

A variety of food samples were purchased and digested for analysis. Microwave-assisted digestion (Mutiwave 3000, PerkinElmer, Shelton, Connecticut) was used following the program in Table I, taking approximately 0.5 g of sample in replicate and using 6 mL of nitric acid and 1 mL of hydrochloric acid (acids were Optima grade and were obtained from Fisher Scientific, Pittsburgh, Pennsylvania).

Table II: ICP-OES conditions

The samples were analyzed using ICP-OES and ICP-MS using the parameters listed in Table II and Table III.

Results and Discussion

Table III: ICP-MS conditions

The samples were chosen to represent a variety of matrices for analysis. The U.S. FDA import alerts were used for guidance on what types of food samples had shown unacceptable levels of toxic metals when tested for import. Although similar matrices were chosen, predigestion spikes were used to demonstrate an elevated level of metals, because the samples were not expected to be contaminated. Table IV shows some of the items listed in import recalls, the country of origin, the contaminating element, and the levels observed in testing.

Samples purchased from a local grocery store included the following foods and beverages:

Orange soda drink — 1 (Mexico)

Orange soda drink — 2 (Canada)

Grape juice (origin not stated)

Guanabara nectar — canned (Mexico)

Raisins (California)

Apricots (Turkey)

Lollipops (Mexico)

Lollipop inner wrappers (Mexico)