TPCH testing protocols - KTRE.com | Lufkin and Nacogdoches, Texas

TPCH testing protocols

Sample Preparation Methods
Plastics, Some Inks: Many labs use EPA Methods 3050B or 3051 for sample preparation. These methods are described as providing "total metals;" however, the methods were designed for hazardous waste and site characterizations. For the purposes of product or package component testing, the goal is to determine the true presence and total concentration of metals in the component. In practice, TPCH has found that these methods are NOT sufficiently aggressive to completely digest/dissolve plastic matrices. In fact, the method summary for EPA Method 3050B states that it is NOT the proper method for preparing samples where total metals concentration is desired. Instead, EPA Method 3052 provides an aggressive acid and microwave energy combination to effectively break down the organic matrices such as plastics and some inks. Although EPA Method 3052 prescribes the use of hydrofluoric acid (HF) in some instances, HF is not required for effective digestion of typical plastic/PVC type package components. Rather, HF is required ONLY if the matrix is siliceous (i.e., contains silica) in nature.

The key parameter to be reported is the extent of dissolution of the matrix, with 100% being the acceptable target. Some trial and error may be expected when testing a new packaging component.

It is important to note that the goal of analytical testing is to determine the total concentration of the four regulated metals. For any analytical method to accurately measure the total concentration of metal, the metal must be completely liberated from the matrix. To achieve this, the matrix must be completely digested, dissolved, or broken down. Therefore, proper sample preparation is critical to obtain meaningful results. The choice of sample preparation depends on the type of sample (matrix). All methods used must carefully document the amount of sample digestion, with 100% dissolution as the goal.

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