Determination of carbon content in soil humus by electric heating oven with constant temperature heating method Wang Haizhen, Xu Jianming, Xie Zhengmiao (Institute of Soil Water Resources and Environment, Zhejiang University, Hangzhou 310029, China) The carbon content of soil humus. The results show that there is no significant difference between the heating of the electric oven at 150 °C for 30 40 min and the oil bath method, but the correlation between the method of heating for 30 min and the oil bath method is more significant (Y=1.0082X+0.0003, r= 0.9992*). The 150C drying oven constant temperature heating method has the advantages of simple operation, good reproducibility, and no secondary pollution in the laboratory.
The organic carbon content of soil is an important chemical indicator of soil quality. At present, the determination of soil organic carbon is generally carried out by analyzing the carbon content of soil humus by the traditional oil bath potassium dichromate capacity method (referred to as oil bath method). Usually, the extract is neutralized with 0.5mol/L H2SO4 first, so that the pH is 7 (tested with pH test paper), and then the extract is placed in a water bath (or electric fund project: National Natural Science Foundation of China (49871044) The National Key Basic Research Development Program (G1999011809) is a study of soil chemistry and environment.
The plate was evaporated to dryness at 80 C, and then the organic carbon content was measured by an oil bath method. However, this method is not only cumbersome, time consuming, and reproducible, but also has problems such as difficulty in controlling the heating temperature and difficulty in cleaning the test tube. If the pH is high, the pH of the soil humus extract will cause the catalyst to be lost. Live, which affects the life and accuracy of the instrument. In recent years, new microwave technology has been used to determine the organic carbon content of soil, but it requires microwave ovens and special equipment such as acid-resistant, alkali-resistant and high-temperature resistant polytetrafluoroethylene raw material sealed containers, which have not been popularized in China. Therefore, this paper has studied comparatively. Using 150C electric dry carbon content, the aim is to find a simple, fast and accurate measurement method to replace the traditional oil bath method.
1 Test materials and methods 1.1 Instruments and equipment 1.2 Test material quality field, yellow soil and red sticky soil and other five kinds of soil loose state and stable humus extract (according method) 1.3 reagent 0667mol / L heavy chromium Potassium acid solution: Weighed at 130 ° C for drying (3 ~ 4h) of analytically pure potassium dichromate 19. In a small beaker, add a small amount of water to dissolve, wash into a 1000 mL volumetric flask without loss and set the volume to 033mol / L Ferrous sulfate solution: Weigh FeSO*. 7H2 (secondary) 9.1747g, dissolve in water and add 50mL of concentrated sulfuric acid. After cooling, dilute with water to 1L. The exact concentration of this solution is calibrated to the reference solution of 0.0667mol/L K2C12O7. Mol / LBSO4 solution: Take the above concentrated sulfuric acid 28.3mL, dilute with water to 1L o-phaloline indicator: according to the preparation.
1.4 Test method 100 objective soil 0.5g (or less than Q5g, and the organic carbon content does not exceed 8mg) placed in a triangular flask, add 10mL0. 0833mol / L potassium dichromate solution and 15mL concentrated BSOs and then put into the electric oven Heated inside. Among them, the molar concentration of potassium dichromate solution, heating temperature and heating time are different in each test, such as the minimum heating temperature is 120 * C, the highest is 210 * C, and the heating time varies from 1.5 to 120 min. On the basis of previous studies, this paper improves the method for determining the carbon content of soil humus by the constant temperature heating method of 150*C electric drying oven. The operation procedure is as follows: accurately extract 4.00mL extract into a 100mL flask. Paper test); Accurately add 1. Potassium chromate solution; slowly add concentrated H2SO45mL, and continue to stir (two blank tests at the same time); quickly put the sample and a blank (the other blank does not need heating) The temperature has risen to 150C in an electric drying oven, heated at a constant temperature for 20 30 and 40 min, and taken out after cooling; rinse the wall of the flask with distilled water to a total volume of about 50 mL; then add 2 to 3 drops of o-parocene indicator. Shake well, at this time the solution is orange-yellow; titrate with 0.033mol / L ferrous sulfate, the content is continuously shaken during the titration process, until the color of the solution changes from orange yellow to blue green and finally to brick red, which is the end point of titration. The results are calculated by the following formula (Vhb-V), VHB is the number of FeS4 ml consumed by the blank test for titration heating, V* is the number of FeS4 ml used for the titration unheated blank test, and V is the FeSCH ml used for titrating the sample. M is the molar concentration of FeS4; 0.003 is the molar mass of 1/4 carbon atom (g/mmol); W is the dry soil sample weight (g); E is the total volume of the extract (mL), as in this paper 200mL; S is the volume of the extracted extract (mL), in this paper is 4.2. Results and analysis 2.1 Comparison of the reproducibility of the results of different methods. The loosened state of the five different soils, the stable state of humus carbon The amount of the test was carried out by the oil bath method (denoted as A method) and the 150C electric drying oven for 20 minutes (denoted as B method) for 30 minutes (denoted as C method) for 40 minutes (denoted as D method). Two parallel determinations were performed each time, and the reproducibility of the results of the four different methods was compared (Table 1). As can be seen from Table 1, the standard deviation (S) and coefficient of variation (CV) of the results of the four methods were all Smaller. The average standard deviation of the oil bath method (A) is 0. 0024%, the average coefficient of variation is 0.5015%; the average standard deviation and the average coefficient of variation of the 150C electric drying oven for 20 minutes (B) are 0.0055% and 1.1056%, respectively; The average standard deviation of heating for 30 min (C) was 0.0013%, the average coefficient of variation was 0.3178%; the average standard deviation of heating for 40 min (D) and the flat 0-5 l/LoO. a and the extract to cPHMlPH test kPu basket The standard deviation and coefficient of variation of the measurement results of heating for 20 min are the highest, indicating that the reproducibility of this method is the worst. 2.2 The effect of heating time on the measurement results can be seen from Table 1. Different heating in 150*C electric drying oven Time, the results of the measurements are also different. Generally, the longer the heating time, the smaller the standard deviation and the coefficient of variation, the repeatable two-way ANOVA of the results of the four methods. The results show that there may be significant differences between some methods and other methods (F+= 198.999>5 =284) Then multiple comparisons were made between the averages of the various measurement methods. It was found that there was no significant difference between the 150*C electric drying oven and the oil bath method for 30 minutes and 40 minutes, and the difference between the measurement method of heating for 20 minutes and the other three methods. All of them reached a very significant level. The reason may be that after the heating for 20 minutes, the sample solution has not been completely digested and the oil bath method is used as the standard. The correlation analysis of these three insignificant measurement methods (average value) shows (Table 2) There is a very significant correlation between the 150*C electric drying oven and the oil bath method. The correlation between the method of heating for 30 minutes and the oil bath method is higher. According to the oil bath method and 150*C electric drying oven for 30min, the results of the determination of the carbon content of the loosened and stabilized humus of the five soils (average value) can be fitted to the regression equation Y=1. 0.9992* Y, Y is the measurement result of the oil bath method, and X is the measurement result of the 150*C electric heating oven heated at a constant temperature for 30 minutes. It can be seen that the content of soil humus is determined by the oil bath method under the constant temperature heating of 150*C electric drying oven for 30 minutes. The amount of carbon is a more feasible method. The results of different measurement methods are compared. The comparison of the results of the different methods of measurement in the purple-green field, the yellow-spotted field, the yellow-soil field, the red-soil field, the loose-stable state, the stable state, the loose state, the stable state, the loose state, the stable state Junction steady state loose state steady state Note: X is the average of 6 measured values, S is the standard deviation, CV is the coefficient of variation. Table 2 Correlation coefficient table method between different determination methods (steady state humus) (Conjunction humus) 3 Conclusion 1 Compared with the oil bath method, the use of a triangular flask to reduce the number of times of washing and transfer at 150 ° C, the operation is simple, rapid, reproducible, and does not pollute the air, suitable For large-volume sample determination, it can be used as a conventional tiller 3.2 test and test The statistical analysis of the results shows that the 150*C electric drying oven can replace the traditional oil bath method for 30min, which can be used for the determination of carbon content in soil humus and can be used for the analysis and determination of organic carbon in water samples or other extracts. Determination of the carbon content of fulvic acid humic acid 3.3 150*C electric drying oven heating method for the determination of stable humus with low carbon content, its reproducibility is good, and the correlation with the oil bath method is high, but When measuring the sample with slightly higher carbon content, the reproducibility and the correlation with the oil bath method are slightly worse. The reason is whether the temperature is not high enough in this test or the concentration of potassium dichromate is low. Therefore, the test method of 150*C electric drying oven for 30 minutes at a constant temperature is more suitable for the determination of trace organic carbon in soil extract or other water samples.
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