Precautions for sample pretreatment for heavy metal determination

1.

(1) Foods with high fat content are prone to bumping during carbonization and are flammable at the same time.

(2) Samples with a lot of sugar, protein , and starch will foam and overflow quickly when carbonized.

(3) For grains and products with a lot of phosphorus, the phosphate will wrap and precipitate during the ashing process.

(4) Some elements are greatly affected by the ashing temperature.

(5) The loss of some elements is due to their volatile form in the sample

2.

(1) After adding nitric acid and sulfuric acid, it should be heated slowly on a low fire.

(2) Add nitric acid along the bottle wall in time

(3) When adding digestive liquid such as nitric acid, it is best to remove the digestion flask from the electric furnace and add it after cooling

(4) If sulfuric acid is used in the digestion (during colorimetric analysis), water should be added to remove the remaining nitric acid, so as to prevent the generated nitrosyl sulfuric acid from destroying the organic color developer and causing serious interference to the determination

(5) The amount of reagents used for wet digestion is large, and the purity of the reagents has a greater impact on the results of the experiment, so attention must be paid in the experiment

(6) At the end of the digestion, a large droplet remains in the digestion tube, and it is white or yellow, as shown in Figure 3-2

Figure 3-2 The end point of mixed digestion

3.

(1) The same or similar samples are generally selected for the same batch of samples

(2) The sample size is generally not more than 0.

(3) For samples that react violently after heating, it is recommended to pre-digest or soak overnight
.

(4) It is not recommended to process samples containing organic solvents.
For example, alcohol and nitric acid will explode when microwave digestion
.

(5) The same kind of sample will also produce different pressures due to the difference in the weighing amount, which results in a difference in the digestion effect
.

(6) Cool to a safe temperature (below 50°C) before proceeding to the next step
.