Acetyl acetone phosphorescication method to determine the uncertainty assessment of free formaldehyde content in water-based coatings

1 Measurement method and measurement process
1. 1 Measurement method
(1) according to national standards (GB 18582 - 2001) "The interior decoration material interior wall paint in the limit of harmful substances."
(2) instrument equipment and dlight measurement are in accordance with the relevant provisions of the above-mentioned national standards.
1. 2 Measurement process
(1) sample is stirred evenly and weighed with an electronic balance, as in this example, the sample is called 2 g, accurate to 0. 001 g
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.
(2) sample is placed in a distilled bottle pre-selected to add 50 ml of water, shake well and add 200 ml of water.
(3) heating distillation, collect distillation to 200 ml.
(4) to 250 ml of distillate.
(5) Take 5 ml of fixed-capacity fractions, add 1 ml of acetyl acetone solution, heat in a boiling water bath at 100 degrees C, keep 3 min, cool to room temperature and use a 10 nm absorption pool to determine the absorbance at the 412 nm wavelength of the phosphorescometer.
(6) calculation, the content of free formaldehyde contained in the unit mass sample is reported, expressed in terms of how many grams of formaldehyde are contained in each kg sample.
2 Mathematical Model and Uncertainty Source Analysis
2. 1 Mathematical model
formula for free formaldehyde content (W) in water-based coatings:
W is 0. 05 × BS (A - A0) /m (1)
: BS——— calculation factor
A——— absorbent of the sample solution
A0——— absorbent of the blank solution
m——— sample amount
2. 2 Uncertainty Source Analysis
As can be known from the mathematical model, the uncertainty of formaldehyde content in water-based coatings mainly includes: relative standard uncertainty introduced in sample weighing, relative standard uncertainty introduced in the measurement of drawing standard curves, relative standard uncertainty of fixed capacity and fractional distillation liquid product, and relative standard uncertainty introduced by measurement repeatability.
3 Assessment of the standard uncertainty component
3. 1 The legal maximum allowable error for the scale
used in the sample weighing is ± 1 mg, which is evenly distributed, and the standard uncertainty of the scale is 1 / 0. 577 mg. Since the balance is used 2 times at weighing time, 1 time for empty container mass, and 1 time for the quality of the container plus sample, the standard uncertainty of the sample is: u(m) - 0. 816 mg.
assumes that the sample mass m is 2. 000 g, its relative standard uncertainty is: urel (m) s u (m) /m s 4. 08 × 10 - 4.
3. 2 The relative uncertainty (X) introduced by the drawing standard curve in the measurement and
the relative uncertainty introduced by the drawing standard curve mainly include:
3. 2. 1 The relative standard uncertainty of formaldehyde standard solution is
given by the standard substance certificate and provided by the Standard Sample Research Institute of the State Environmental Protection Administration, and its relative uncertainty is 0. 03 (k s 1), then the relative standard uncertainty is: urel (c0) s 0. 03。
3. 2. 2 Relative standard uncertainty ( x0 )
resulting from linear regression of the standard curve , the absorption value yi is measured from the instrument by measuring the blank and a series of standard solution xi , and the linear regression of the data is shown in Table 1 . 041 5 x 0. 014 5。 Where the slope b is 0. 041 5, intercept a s 0. 014 5, r s 0. 999 8。
: the number of times the
n—————— test calibration solution calculated after the xi substitute correction curve
n——— the amount of formaldehyde in the distillate
x0——— the amount of formaldehyde in the distillate
p——— the number of times the test x0 (p s 3)
x——— the average of different calibration standard solutions (5. 429 μg)
this measurement, the sample vaporizer formaldehyde content determination value x0 . 952 μg, so the relative standard uncertainty generated by the linear regression of the standard curve is: urel ( x0 ) s u (x0) / x0 s 0. 048 7。
3. 3 250 ml capacity bottles and 5 ml pipe are used for fixed capacity and fractionation of distilled liquid product relative to standard uncertainty
and fractional distillation, of which the allowable error of 250 ml capacity bottles is ± 0. At 20 ml, the relative standard
the introduction of the standard deviation of the ml pipe is 0. 000 708 and 0. 002 88。 Therefore, the relative standard uncertainty of fixed capacity and fractionation distilled liquid product is:
5 extended uncertainty
including factor k take 2, then the standard expansion uncertainty of the sample is: U(w) - k × u (w) ≈0. 005 9 g / kg.
of the results of
the determination of formaldehyde content in water-based coatings using acetyl acetone phosphorescicity can be found in the following form: w s w s u (w) s 0. 048 8 ± 0. 005 9 g / kg.
7 Conclusions and Explanations
(1) Can be seen from the above component results: The uncertainty of formaldehyde standard solution, the error of formaldehyde in the working curve calculation distillation and the standard deviation of the measurement standard including the repetition of the steaming process are the main contributing factors of this method uncertainty, so the linearity of the working curve and the repetition of the determination are the key to correctly grasp this method.
(2) Although more factors are considered in this paper, there are still some such as the volume of the appropriate amount of water pre-added in the distillate receiving vessel, the degree of ice cooling outside the receiving vessel, the time of distillation placement, the influence of temperature and the influence of acetylacetone contrast color, etc. need to be further tested.