The pretreatment of samples is a complex task when analyzing test substances, and it holds significant importance in the overall analysis and detection process. It also plays a crucial role in identifying the source of detection errors. This article aims to summarize four fundamental pretreatment methods used for samples in atomic absorption spectrometry (AAS) analysis. Additionally, it discusses the basic detection methods for six types of samples commonly encountered in routine analysis and detection. These methods are practical and can serve as valuable references for users of AAS instruments.

Wet Digestion Method:

For samples weighing approximately 0.1000 to 0.5000g, the commonly used approach involves utilizing mixed acids. The following acid ratios are often employed:

(1) HNO3:HCLO3 = 5:1

(2) HNO3:H2SO4 = 5:1

(3) HNO3:HCl = 5:1

(4) Pure HNO3

Note: It is crucial to avoid the presence of volatile (acetone, ether, ethanol, etc.), flammable, and explosive substances during the digestion process. The wet digestion method is widely employed and well-known, so further elaboration is unnecessary.

Dry Ashing Method:

Typically, samples weighing between 2.000 and 5.000g are treated using the dry ashing method, which prevents volatilization. The procedure involves placing the sample in a porcelain crucible, adding a few drops of water to wet it, followed by a small amount of concentrated nitric acid. Heat is then applied to carbonize the sample over a low flame. The crucible is subsequently transferred to a muffle furnace for ashing at approximately 550°C for 2 to 4 hours. After cooling, the ash (colorless or light in color) is dissolved using other acids, often in a 1:1 ratio with nitric acid (varies depending on the sample). The solution is then filtered, adjusted to volume, and aliquoted into 10mL, 25mL, and 50mL portions for further use.

High-Pressure Tank Method (Using a Lidded Tank Made of Polytetrafluoroethylene):

When the sample weighs less than 0.3000g, this method is employed. It involves adding 6mL of mixed acid and 1mL of HF(H2O2) to the sample. The autoclave is sealed, and the sample is heated at 160°C for 5 hours. After cooling, the solution is filtered and adjusted to the desired volume for subsequent analysis.

Microwave Digestion Method:

The microwave digestion method utilizes commonly used mixed acids, including:

(1) HNO3:HCLO3

(2) HNO3:H2SO4

(3) Pure HNO3

Note: The choice of specific acid for digestion varies depending on the sample. Readers are encouraged to select the appropriate acid accordingly.

AAS Analysis and Detection Methods for Various Samples:

Analysis of Pb, Cd, As, Mo, Cr, etc. (Graphite Furnace AAS Method):

For Pb analysis, a 1.0mL sample is diluted to 10mL with 1% HNO3. The linear range is 0 to 20ng/mL, with drying temperature set between 80 and 100°C, ashing temperature at 200°C, and atomization temperature at 1500°C.

For Cd analysis, a 1.0mL sample is diluted to 10mL with deionized water. The linear range is 0.1 to 0.4ng/mL, with the same drying, ashing, and atomization temperatures as Pb.

For As analysis, a 1.0mL sample is combined with 100μL of Ni (2mg/mL) and diluted to 10mL with 1% HNO3. The linear range is 0 to 4ng/mL, with the same drying, ashing, and atomization temperatures as Pb.

For Mo analysis, a 1.0mL sample is diluted to 10mL with 1% HNO3. Pd is used as the modifier, and the linear range is 0 to 20ng/mL, with the same drying, ashing, and atomization temperatures as Pb.

For Cr analysis, 1mL of the sample is diluted to 100mL with deionized water. The linear range is 0 to 40ng/mL, with the same drying, ashing, and atomization temperatures as Pb.