Preface
Soy sauce is a traditional condiment in China. It is a liquid condiment usually made from soybeans, black beans, salt and other ingredients through oil making and fermentation. Therefore, the composition of soy sauce is relatively complex and rich in sodium salt, amino acids, sugars, pigments, spices, etc. For the analysis of multiple elements in condiments such as soy sauce, pretreatment usually uses wet digestion, microwave digestion and other methods. The digested solution is acidified and then the elements are determined on ICP-MS. This pretreatment is time-consuming and involves contact with different corrosive and toxic reagents. Therefore, this experiment uses SUPEC 7000 ICP-MS. The soy sauce is diluted with 2% nitric acid and directly injected. By adjusting the ratio of online dilution gas to nebulizer gas, the soy sauce sample can be stably and continuously injected.
Experimental part
Instrument parameters
The SUPEC 7000 ICPMS has an optional online dilution system. In the determination of high-matrix samples, the system can be optimized to perform online dilution of high-matrix samples to avoid matrix effects caused by high matrices and affect the accuracy of measurement results.
Figure 1 SUPEC 7000 ICPMS
Instrument parameters
Table 1 Instrument parameters
| power | 1500W |
| Nebulizer gas ( mL /min) | 0.650 |
| Dilution gas ( mL /min) | 0.600 |
| Collision gas (mL/min) | 0.800 |
| Sampling depth ( mm) | 3.590 |
| Atomizer lift | 0.1ml/min |
Reagents and sample preparation
Sample: Commercially available light soy sauce
Nitric acid: high purity
Ultra-pure water
Multi-element mixed standard
Sample preparation
Take 0.5 mL of soy sauce sample, dilute to 25 mL with 2% HNO3, and test directly on the machine.
Result analysis
standard curve line
R 2 of each element is above 3 9. Figure 2 is the linear fitting diagram of some elements.
The detection limit
The method detection limits of 22 elements were calculated by 3 times the standard deviation obtained by analyzing the blank sample 11 times. As shown in Table 2, the detection limits of each element can meet the requirements of GB 5009.268-2016.
Table 2 Detection limits of each element (unit: ng/mL)
| 9Be | 11B | 26Mg | 27Al | 49Ti | 51V | 52Cr | 55Mn | 54Fe | 59Co | 136Ba |
| 0.022 | 1.247 | 0.871 | 0.382 | 0.088 | 0.047 | 0.020 | 0.025 | 0.750 | 0.007 | 0.026 |
| 60Ni | 65Cu | 66Zn | 71Ga | 75As | 86Sr | 111Cd | 116Sn | 123Sb | 208Pb | |
| 0.044 | 0.023 | 0.204 | 0.006 | 0.062 | 0.097 | 0.011 | 0.018 | 0.010 | 0.007 |
Precision
Select sample brand 2 , scan it 7 times continuously, and calculate the precision of each element. As shown in Table 3, the RSD% of each element is less than 3%.
Table 3 Precision of each element (n=7)
| 11B | 27Al | 49Ti | 51V | 52Cr | 55Mn | 54Fe | 59Co | |
| Average value (μg/L) | 45.65 | 13.75 | 0.37 | 0.28 | 0.75 | 106.59 | 110.81 | 0.21 |
| SD | 0.80 | 0.34 | 0.01 | 0.01 | 0.01 | 1.69 | 2.01 | 0.00 |
| RSD( %) | 1.8 | 2.5 | 2.7 | 3.8 | 1.9 | 1.6 | 1.8 | 2.2 |
| 60Ni | 65Cu | 66Zn | 71Ga | 75As | 86Sr | 136Ba | 208Pb | |
| Average value ( μg /L) | 19.11 | 0.67 | 73.98 | 0.0115 | 0.40 | 17.37 | 15.76 | 0.34 |
| SD | 0.34 | 0.01 | 1.98 | 0.00 | 0.01 | 0.60 | 0.27 | 0.01 |
| RSD( %) | 1.8 | 1.9 | 2.7 | 2.8 | 2.8 | 3.5 | 1.7 | 1.9 |
Spike recovery
The spike recovery experiment was carried out on sample brand 3 , and the results are shown in Table 4 (Mg , Fe, and Mn were not spiked due to their high content ). The recoveries of all spiked elements were between 89.5% and 118.1%, and the data results were reliable and met the determination requirements.
Table 4 Sample spike recovery results (unit: μg /L)
| element | 9Be | 11B | 27Al | 49Ti | 51V | 52Cr | 59Co | 60Ni | 65Cu |
| measured value | 0.000 | 38.800 | 42.330 | 0.337 | 0.631 | 1.502 | 0.228 | 16.690 | 0.547 |
| Added amount | 0.500 | 5.000 | 5.000 | 0.500 | 0.500 | 0.500 | 0.500 | 5.000 | 0.500 |
| Spiking results | 0.510 | 43.600 | 46.873 | 0.889 | 1.078 | 2.012 | 0.742 | 22.431 | 1.132 |
| Recovery rate(%) | 102.0 | 96.0 | 90.9 | 110.4 | 89.5 | 102.0 | 102.9 | 114.8 | 116.9 |
| element | 66Zn | 71Ga | 75As | 86Sr | 111Cd | 116Sn | 123Sb | 136Ba | 208Pb |
| measured value | 45.387 | 0.023 | 0.525 | 18.010 | 0.036 | 0.000 | 0.000 | 13.164 | 0.672 |
| Added amount | 5.000 | 0.500 | 0.500 | 5.000 | 0.500 | 0.500 | 0.500 | 5.000 | 0.500 |
| Spiking results | 50.708 | 0.521 | 1.101 | 23.219 | 0.543 | 0.492 | 0.466 | 18.331 | 1.263 |
| Recovery rate(%) | 106.4 | 99.6 | 115.3 | 104.2 | 101.3 | 98.5 | 93.3 | 103.3 | 118.1 |
in conclusion
This experiment used S UPEC 7000 ICPMS, through gas dilution sampling, established a method for direct sampling of soy sauce to determine multiple elements. This method does not require digestion, making pretreatment more convenient and quick. The experimental data also showed that the test results were reliable, the multi-element annotation curve R 2 > 0.999, the sample spike recovery rate was between 8 9% and 118%, and the stability was < 3%.
