Determination of 60 semi-volatile organic compounds in soils and sediments by gas chromatography-mass spectrometry (3)

7.

(1) Qualitative target compound

Qualitatively based on the retention time of each component of the standard substance and the comparison of the standard mass spectrum

(2) Quantitative calculation

1.

The relative response factor RRF _i of the target (or substitute) in the ith point of the standard series is calculated according to formula (1)

In the formula, A _i —— the response value of the quantified ion of the ith point (or substitute) in the standard series;

A _{ISi ——The} response value of the internal standard quantitative ion corresponding to the i-th target (or substitute) in the standard series;

p _{IS ——the} mass concentration of the internal standard substance in the standard series;

p _{i ——the} mass concentration of the target substance (or substitute) at the i-th point in the standard series

The average relative response factor of the target (or substitute) is calculated according to formula (2)

(2) In the formula, n——the number of standard series points

2.

When the target (or substitute) is calibrated with the average response factor, the mass concentration p _ex (ug/L) of the monthly standard (or substitute) in the sample is calculated according to formula (3)

In the formula, A _x —— the response value of the quantitative ion of the target (or substitute);

A _{IS ——The} response value of the internal standard quantitative ion corresponding to the target (or substitute);

p _IS ——the mass concentration of the internal standard substance, ug/L;

——The average relative response factor of the target (or substitute)

3.

In the formula, p _i ——the mass concentration of the target compound calculated from the calibration curve, mg/L;

V——The constant volume of the sample, mL;

m——Sample mass (wet weight), g;

w _{dm ——The} dry matter content of the sample, %

8.

(1) At least one full procedure blank should be analyzed for each batch of samples

(2) Before the analysis of each batch of samples or within 24 hours, it is necessary to check the performance of the instrument, determine the calibration confirmation standard sample decafluorotriphenylphosphine (DFTPP) and the blank sample

(3) The configuration of the standard series should be at least 5 points, and the configuration mass concentration range should cover the mass concentration of the sample to be tested

(4) Each batch of samples should be subjected to parallel analysis and matrix spike analysis
.
The recovery rate of the standard addition of the substitutes and the matrix in all samples should meet the recovery rate range of the corresponding compound in Appendix D of HJ834-2017
.
The relative deviation of parallel samples should be within 30%
.

Nine, matters needing attention

(1) The cleanliness of the sampling system affects the peak shape and response of some compounds.
Prepare a mixed solution containing 4,4'-DDT, pentachlorophenol and benzidine with a mass concentration of 50ug/mL to check the gas chromatograph injection Dirty status of the system
.
If the degradation rate of DDT to DDE and DDD exceeds 15%, the peak shapes of polar compounds such as benzidine and pentachlorophenol appear tailing and splitting, etc.
, the inlet needs to be maintained, such as replacing the liner and cutting the chromatographic column.
For part of the front end, the sample analysis can be continued after repeating the above inspection and passing
.

(2) The peak shape of nitrobenzene on the chromatographic column may be branched and tailed.
When performing quantitative integration, pay attention to the occurrence of this situation and judge the accuracy of its integration in time
.

(3) Analysis phthalate time-based plasticizer, should be taken to prevent the introduction of contamination blank laboratory reagents main source of contamination, diatoms, filters, etc.
, to deal with the use of high temperature burning material taken Or solvent cleaning, replacement of high-purity reagents, etc.
, to effectively control the occurrence of positive interference
.

(4) For phenolic substances such as 2,4-dinitrophenol , 4-nitrophenol , 4,6-dinitro-2-methylphenol and pentachlorophenol, because they are in the single quadrupole mass spectrometer This method is not suitable for analysis due to the low response and low fit of the quantitative curve.
Other suitable methods should be selected, such as gas chromatography FID method, LC method and other methods
.

(5) When analyzing actual samples, due to matrix interference, it is often necessary to purify samples after solvent extraction.
There is currently no good universal purification method for the various semi-volatile organic compounds involved in this method.
According to the physical and chemical properties of various compounds and the specific conditions of matrix interference, different purification methods, such as silica gel, alumina, magnesium silicate, and composite materials, are adopted
.