Comparison Between AAS and ICP
Under excitation from external radiation energy at a certain frequency, the spectrum produced when outer electrons of atoms transition from a lower energy state to a higher energy state is the atomic absorption spectrum (AAS). This method has advantages such as low detection limits, high accuracy, good selectivity (i.e., low interference), and fast analysis speed.
Atomic emission spectrum (AES) utilizes the characteristic radiation produced when outer electrons of different atoms or ions in a substance undergo energy level transitions to determine the chemical composition of the substance. This method requires a strong excitation light source, and ICP is an excellent excitation light source. The ICP atomic emission spectrometer is an instrument that performs qualitative and quantitative analysis of various elements based on the atoms or ions of the elements being tested in the sample. This instrument features small sample volumes, wide application range and speed, high sensitivity, and good selectivity.
(1) AAS is more common, relatively cheaper than AES, and easier to operate;
(2) AES is superior to AAS in multi-element determination capability, but AES is more complex to operate than AAS; additionally, AES suffers from more severe spectral interference due to spectral line overlap, while AAS has much less;
(3) Atomic emission has a wider measurement range than absorption, and for ICP, the accuracy is also higher. Some elements cannot be measured by atomic absorption but can be by emission, such as P, S, etc.;
(4) Atomic absorption has lower experimental efficiency; detecting one element requires a corresponding element lamp. If following ICH Q3D requirements, oral products need to test seven basic elements, which with atomic absorption would require seven separate analytical method validations, making the workload too large. ICP belongs to atomic emission, with high throughput; typically, one method can detect all elemental impurities.
Summary: For detection of single elements, especially metal elements, AAS is preferable; for detection of multiple elements, especially non-metal elements, ICP is preferable.
Our company has recently equipped with an ICP spectrometer, which after more than one month of debugging, is now in use and accepts external testing for multiple ions in samples.
How to Better Utilize the ICP Spectrometer
Sample pretreatment is key:
i. Determine the analysis method and weighing amount based on the sample content to ensure the content of the element to be tested is within the detection range of the ICP spectrometer.
ii. Ensure complete decomposition of the sample, with no loss or contamination.
iii. Select an appropriate medium, preferably nitric acid and hydrochloric acid, and minimize the use of sulfuric or phosphoric acid.
vi. Ensure no reagents harmful to the instrument are used (e.g., HF, strong bases, etc.).
