Método Allegra

The alternative method is semi-quantitative, colorimetric, and consists of three stages: pre-treatment, determination, and visual comparison of the color intensity.

Pre-treatment

The purpose of this step is to release all the mercury contained in the sample (matrix) into the test solution. The conditions vary according to the kinds of samples (see details in the Table). This stage uses a system similar to that shown in Figure 1.

Figure 1 - Schematic drawing of the system used for sample pre-treatment: Erlenmeyer & Mini-condenser, known as the "cold finger" technique

Table: Pre-Treatment Conditions for Environmental Samples

Matrix	Mass or Volume	Acid / oxidant mixture	detection limit
Fish	10 g	H2SO5 / HNO3 / V2O5 / KMnO4	100 µg/Kg
Sediments	10 g	HNO3/HCl	100 µg/Kg
Soil	10 g	HNO3/HCl	100 µg/Kg
Solid waste	10 g	HNO3/HCl	100 µg/Kg
Effluents	100 mL	HNO3	10 µg/L
Urine	100 mL	HNO3 / KMnO4	10 µg/L
Air	Variable volume	H2SO4/ KMnO4	According to volume

After weighing and adding the reagents, the mixture is heated for approximately one hour in a double boiler or sand. At the end of the pre-treatment stage, all the mercury present in the sample is now in the test solution, in soluble form (Hg+2).