The intensity of the mass spectrometry signal in splitless injection mode was affected by the inlet temperature (factor A), ion source temperature (factor B), and carrier gas flow rate (factor C). The effects of these three factors on the intensity of the mass spectrometry signal were first investigated separately. The results showed that the peak area of chlorothalonil reached the maximum when the inlet temperature was 260˚C or the ion source temperature was 280˚C or the carrier gas flow rate was 1.2 ml, respectively. Therefore, the orthogonal experiment was carried out according to the conditions in Table 1. The peak area under the nine experimental conditions was determined, and the k value and the maximum difference of each factor were calculated, thus the optimal scheme was given out, as shown in Table 1. It could be seen from the data in Table 1 that the factor A had the largest maximum difference and the factor B had the smallest maximum difference. Therefore, the factor that had the greatest impact on the peak area was the inlet temperature (factor A), followed by the carrier gas flow rate (factor C) and the ion source temperature (factor B). Through the orthogonal experiment, it was determined that the optimal scheme is A₃B₃C₂, that is to say, the 9^th condition in Table 1. The standard solution was analyzed under this conditions and the obtained GC/MS-SIM chromatogram was shown in Figure 1. A sharp peak corresponding to chlorothalonil appeared at about 5.659 min in Figure 1.

The ultrasonic extraction efficiency depended on four factors such as the type of

extraction solvent, extraction temperature (factor A), extraction time (factor B), and extraction solvent volume (factor C). In order to investigate the effect of Factor A, Factor B and Factor C on the extraction amount, four self-made positive samples were ultrasonically extracted with acetone as the extraction solvent. In each experiment, only one factor changed while the other two factors remained the same. The results showed that the extraction amount reached the maximum when the extraction time was 30 min for sample 1# and sample 2# while the extraction amount reached the maximum when the extraction time was 35 min for sample 3# and sample 4#. The extraction amount reached the maximum when the extraction temperature was 35˚C for sample 2# and 40˚C for sample 1#, sample 3# and sample 4#. The extraction amount reached the maximum when the volume of the extraction solvent was 20 ml, 30 ml, 20 ml and 25 ml for sample 1#, sample 2#, sample 3# and sample 4#, respectively. In order to investigate the combined effects of these three factors on the extraction amount, an orthogonal experiment was designed according to Table 2. Four self-made positive samples were tested under each condition using acetone as the extraction solvent, and the extraction amounts were listed in Table 2. The k value and the maximum difference of each factor were calculated according to data in Table 2 to give out the optimal scheme as shown in Table 3. The results showed that the optimal schemes of sample 1#, sample 2#, sample 3# and sample 4# were A₃B₃C₃, A₃B₂C₃, A₃B₃C₃, and A₃B₃C₁, respectively. Taking all factors into consideration, the final optimal scheme was A₃B₃C₃, that is to say, the extraction temperature, extraction time and extraction solvent volume were 45˚C, 35 min, and 30 ml, respectively. Under the ultrasonic extraction conditions mentioned above, four self-made positive samples were ultrasonically extracted using common solvents such as ethyl acetate, acetone, n-hexane, methanol, ethanol, acetonitrile, dichloromethane, petroleum ether, t-butyl methyl ether, ethyl acetate/dichloromethane (1:1, V/V) and n-hexane/acetone (1:1, V/V) as the extraction solvents. The extraction results were shown in Table 4. Samples of different materials had different optimal extraction solvents. The optimal extraction solvent was ethyl acetate for sample 1# and sample 3# whose substrate was polyester and

cotton, respectively. The optimal extraction solvent was dichloromethane and ethanol for sample 2# and sample 4#, respectively whose substrate was nylon and wool, respectively. In order to ensure that the final optimal extraction solvent had a good extraction effect on all samples, the solvent with the largest total extraction amount was selected as the final optimal extraction solvent. According to the data in Table 4, the total extraction amount reached the largest when ethyl acetate was used as the extraction solvent. Therefore, the ultrasonic extraction conditions were finally optimized as follows: 30 ml of ethyl acetate was used as the extraction solvent, the extraction temperature was 45˚C, and the extraction time was 35 min.

The sensitivity was tested by analyzing a series of standard working solution. Linear calibration curve was studied by plotting the pear areas against the mass concentrations of chlorothalonil. Excellent linearity was found over the range of 0.2 μg/ml to 42.8 μg/ml for chlorothalonil and the correlation coefficient was 0.9999. The limit of detection (LOD) was taken when the ratio of signal to noise (S/N) was three and the limit of detection (LOD) was 0.1 mg/kg for chlorothalonil.

Three levels (1.1 μg, 5.4 μg and 21.4 μg) of chlorothalonil were added to polyester lining cloth, nylon lining cloth, cotton lining cloth and wool lining cloth, which originally contained no chlorothalonil. The spiked average recoveries and the relative standard deviations (RSDs) of nine replicate measurements were determined as shown in Table 5. The spiked average recoveries ranged from 81.9% to 95.4% while the relative standard deviations (RSDs) varied from 1.8% to 5.2%.

The inner-day and inter-day RSDs were used to examine the repeatability of the proposed method. Inner-day precision was evaluated using nine injection containing chlorothalonil at 5.4 μg/ml in 1 day while inter-day precision was assessed using nine determinations containing chlorothalonil at 5.4 μg/ml on different days. The inner-day and inter-day precision (n = 9) for chlorothalonil was 2.5% and 3.9%, respectively, which could be considered acceptable. This result demonstrated that no significant influence of the chlorothalonil stability on the experimental results was found during sample preparation and GC/MS-SIM determination.

To evaluate the applicability of the proposed method, the contents of residual chlorothalonil in 157 commercial textile samples were determined using the previous described procedure. Quantification was based on the external standard method using calibration curves fitted by linear regression analysis. Chlorothalonil was detected in a striped knitted cotton women’s trousers sample and the content of chlorothalonil was 456.3 mg/kg. GC/MS-SIM chromatogram of this positive sample was shown in Figure 2. A sharp peak corresponding to chlorothalonil appeared at about 5.655 min in Figure 2.