When using phenol reagent to measure indoor formaldehyde, is the concentration of the standard substance measured to be low?
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When using the standard HJ/T167-2004 H.2 method to measure formaldehyde in a laboratory, the values obtained fall within the range of the standard curve. Formaldehyde concentration/ug: A A-A0 0.0 0.028 0.000; 0.1 0.064 0.036; 0.2 0.096 0.068; 0.4 0.163 0.135; 0.6 0.230 0.202; 0.8 0.302 0.274; 1.0 0.366 0.338; 1.5 0.528 0.500; 2.0 0.687 0.659. The equation is y=0.3302x+0.0036, with a correlation coefficient of r=0.9998. The concentration of the standard substance is 1.71 ± 0.08 mg/L. When 0.4 mL of this standard substance was used, the absorbance values obtained were 0.196 and 0.194 (for duplicate samples), resulting in calculated concentrations of 1.25 and 1.23 mg/L. Why is there such a large difference in the measured concentrations of the standard substance? Seeking help to analyze the reasons
Switch to the standard HJ/T167-2004 H.4 method for measuring indoor air formaldehyde
Switch to the standard HJ/T167-2004 H.4 method for measuring indoor air formaldehyde
By using the standard HJ/T167-2004 H.4 method for measuring formaldehyde in indoor air, the formaldehyde concentrations are as follows: A, A-A0: 0.0, 0.028; 0.000, 0.5; 0.050, 0.022; 2.0, 0.114, 0.086; 4.0, 0.201, 0.173; 6.0, 0.288, 0.260; 8.0, 0.375, 0.347; 10.0, 0.465, 0.437. The resulting equation is y=0.0436x+0.0006, with a correlation coefficient of r=1. The concentration of the standard substance is 1.71 ± 0.08 mg/L; the volume of this standard substance used was 3 mL, and the absorbance values obtained were 0.254 and 0.253 for the duplicate samples. Thus, the calculated concentrations of the standard substance were 1.72 and 1.72 mg/L. Why is there such a large difference between the concentrations determined by these two methods?