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    Home > Chemicals Industry > Chemical Technology > Determination of lead, cadmium, arsenic, mercury and copper residues in traditional Chinese medicine (3)

    Determination of lead, cadmium, arsenic, mercury and copper residues in traditional Chinese medicine (3)

    • Last Update: 2022-07-01
    • Source: Internet
    • Author: User
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    (4) Determination method

    1.


    (1) Preparation of standard curve solution

    1) Lead standard curve: accurately measure the appropriate amount of lead standard stock solution (1ug/ml) and dilute it with 2% nitric acid solution to make a solution containing 0, 5, 20, 40, 60, 80 ng of lead per 1 ml


    2) Standard curve of cadmium: accurately measure the appropriate amount of cadmium standard stock solution (1ug/ml), and dilute it with 2% nitric acid solution to make a solution containing 0, 0.


    3) Copper standard curve: accurately measure the appropriate amount of copper standard stock solution (10ug/ml), and use 2% nitric acid solution to make a solution containing 0, 0.


    4) Standard curve of arsenic: accurately measure an appropriate amount of arsenic standard stock solution (1ug/ml), and dilute it with 2% nitric acid solution to make a solution containing 0, 5, 10, 20, 30, and 40 ng of arsenic per 1 ml


    5) Mercury standard curve: accurately measure mercury standard stock solution (1ug/ml) 0, 0.


    (2) Determination

    1) Lead determination method: The graphite furnace atomic absorption method is used for the determination of lead


    2) Cadmium determination method: the determination of cadmium adopts graphite furnace atomic absorption method


    3) Copper determination method: the determination of copper adopts flame atomic absorption method


    4) Arsenic determination method: the determination of arsenic adopts the hydride generation atomic absorption method


    5) Mercury determination method: The mercury determination adopts cold vapor atomic absorption method


    2.


    When used for impurity limit inspection, take the test product and prepare the test product solution according to the regulations under each category; take the same amount of the test product and add the solution of the element to be tested in the limit to make the reference solution



    (5) Matters needing attention

    1.


    (1) When using the graphite furnace method, it is recommended to use an autosampler to ensure the precision of sample injection


    (2) Regarding matrix improvers
    .
    Matrix modifier generally refers to adding one or more chemical substances to the graphite furnace or sample solution to make the matrix form volatile compounds, which are driven off before the atomization stage; or to reduce the volatility of the element to be tested to prevent Loss during the ashing process
    .
    It is recommended to use the matrix modifier recommended by the Pharmacopoeia in the determination of lead and cadmium, which helps to eliminate the interference caused by the complex matrix in the test solution
    .
    Due to the strong volatility of lead chloride, when wet digestion is used, perchloric acid , hydrochloric acid , etc.
    are used to make the test solution contain a certain amount of chloride ions, a matrix modifier must be used to prevent lead in the ashing stage.
    Volatilization loss
    .
    For example, when the sample contains chlorine and the matrix modifier is not used, the ashing temperature is higher than 300 ℃, the lead will be volatilized.
    However, after the matrix modifier recommended by the Pharmacopoeia is used, the ashing temperature can be increased to 1000 ℃, which is relatively high.
    The high ashing temperature can effectively promote the decomposition and elimination of the matrix components, and reduce the interference to the determination during the atomization process
    .

    (3) Optimize the ashing-atomization conditions of the graphite furnace
    .
    The measurement conditions listed in the Pharmacopoeia are reference conditions.
    For different instruments and different samples, some measurement conditions may vary.
    Generally, an ashing-atomization curve should be drawn to determine the maximum ashing temperature and the minimum atomization temperature to maximize The degree of interference is eliminated, and the highest sensitivity is obtained at the same time
    .

    (4) Use appropriate background correction
    .
    Background correction is an important means to eliminate the interference of background molecular spectra in graphite furnace analysis
    .
    Different manufacturers' instruments may have different background correction methods.
    Generally, the deuterium lamp method and Zeeman method are the most commonly used
    .
    The Er lamp method has strong calibration ability, but because it needs to introduce a second light source, it is necessary to pay attention to the collimation of the light path; Zeeman method does not need a second light source, it is convenient to use, and the results are accurate, but the instrument purchase cost is slightly higher, and the sensitivity is higher than that of the deuterium lamp method.
    Slightly lower
    .

    2.
    Precautions for the determination of copper by the flame method Copper is convenient to use the flame method for measurement, with little interference, good precision and accurate results
    .
    Attention should be paid to adjusting the acetylene-air-gas ratio and the height of the combustion head in order to obtain the best sensitivity
    .

    3.
    Precautions for the determination of arsenic and mercury by the hydride method

    (1) The acidity of the solution has a great influence on the sensitivity of the determination.
    Keep the acidity of the control solution, test solution and blank solution consistent
    .

    (2) The stability of mercury is poor.
    Adding an oxidizing agent can enhance the stability of mercury, but it is still recommended to complete the measurement as soon as possible after the solution is prepared
    .

    (3) The stability of sodium borohydride (or potassium borohydride ) solution is poor, and it needs to be newly prepared for immediate use
    .

    (4) Arsenic and mercury are highly toxic, and ventilation should be strengthened during the determination to ensure safety
    .

    (6) Standard curve and linear range

    When preparing the standard curve, one-variable linear regression is generally used, but in the case of a narrow measurement linear range, the quadratic equation least squares fitting regression can better reflect the true concentration-absorbance relationship
    .
    Generally, r≥0.
    995 is required
    .
    The measured value of the sample should be within the linear range of the standard curve.
    If the absorbance value is higher than the standard curve, it should be appropriately diluted before the measurement
    .

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

     

     

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