Determination of lead, cadmium, arsenic, mercury and copper residues in traditional Chinese medicine (2)

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(1) Basic concepts

Atomic absorption spectrophotometry is also known as atomic absorption spectroscopy.

Atomic absorption spectrophotometry is a relatively mature analysis technique, which is generally considered to have the following advantages:

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The main disadvantage of the atomic absorption spectrometry is that it is still a single element measurement method, that is, the hollow cathode lamp of the element needs to be replaced for each element measured, which makes the measurement efficiency low

(2) General requirements for instruments

The atomic absorption spectrophotometer is composed of a light source, an atomizer, a monochromator, a background correction system, an automatic sampling system, and a detection system

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(1) Flame atomizer: It is composed of main components such as atomizer and burning lamp holder

(2) Graphite furnace atomizer: It is composed of electric graphite furnace and power supply

(3) Hydride generation atomizer: It is composed of a hydride generator and an atomic absorption cell, and can be used for the determination of arsenic, germanium, lead, cadmium, selenium, tin, antimony and other elements

(4) Atomizer for cold vapor generation: It is composed of a mercury vapor generator and an atomic absorption cell, and is specially used for mercury determination

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In the flame method atomic absorption determination, you can use methods such as selecting the appropriate measurement line and slit, changing the flame temperature, adding complexing agents or release agents, and using standard addition methods to eliminate interference; in the graphite furnace atomic absorption determination, you can use options Appropriate background correction system, adding appropriate matrix modifiers and other methods to eliminate interference
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The specific method should be selected according to the regulations under each category:

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The detection system is composed of a detector, a signal processor and an indicator recorder.
It should have high sensitivity and good stability, and be able to track the rapid changes of the absorption signal in time
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(3) Standards and working reference materials

The single-element standard solution issued by the Chinese Academy of Metrology is accurate and easy to use
.
Generally, it is first diluted to prepare a single-element standard stock solution with a concentration of not less than 1ug/ml, stored in a plastic airtight container, and stored at low temperature for a long time, which is convenient for use
.
For each measurement, prepare a standard use solution in accordance with the concentration and method specified in the Pharmacopoeia
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The analysis of heavy metals and harmful elements in traditional Chinese medicine belongs to the category of trace determination.
There are many influencing factors, and the environment, reagents, operation, etc.
will cause great interference to the determination.
Therefore, it is recommended to carry out a work comparison with each test to check whether the determination result is reliable
.
The working reference material can be selected as the national first-level standard material "poplar leaf" or "citrus leaf" provided by the Chinese Academy of Metrology.
The matrix composition of this standard material is close to that of Chinese medicinal materials, including lead, cadmium, arsenic, mercury, copper and other elements.
Similar to common Chinese medicinal materials, each measurement is accompanied by a working control.
When the measured value of the working reference substance is consistent with the standard value, the measurement result of the sample can be considered to be reliable
.
However, it must be pointed out that the accompanying work control cannot completely replace the recovery experiment.
Because of the different composition of the matrix of different Chinese medicines, it is still recommended to add samples to the recovery experiment when testing samples that have not been investigated
.