I am working on a instrument called LICOR-8100A soil CO2 flux system but their are some problem in their functioning. so I am looking for a alternative method. If someone have solution of this problem, Please let me know
Progress of work
1. Determination of carbonates.
Methods for determining the content of carbonates in the soil are based on the weight, volume or gasometric determination of CO2 displaced during the destruction of carbonates.
The simplest and fastest methods are: volumetric, based on the destruction of carbonates with a titrated acid solution, followed by the determination of excess acid by alkali, and bulk, based on taking into account the loss of soil mass due to the removal of CO2 during the destruction of carbonates by acid. The volumetric method is applicable at high, the weight method is applicable at any content of carbonates.
From a soil sample sifted through a sieve with holes of 1 mm, a weight of 2 to 5 g is taken on analytical scales (depending on the content of carbonates: the larger it is, the smaller the weight). The suspension is placed in a flask with a capacity of 750-1500 ml, 500-1000 ml of a titrated HCl solution is poured. With a CO2 content of carbonates in an amount of up to 15%, 0.02 n HCl solution is used, with a CO2 content of carbonates from 16 to 18% – 0.1 n HCl solution, and in the case of a very high amount of CO2 (more than 18%), 0.2 n HCl solution in a volume of 250 ml is used. The suspension of the soil is infused with hydrochloric acid during the day, periodically shaking it. It is impossible to close the flask with a stopper, since the reaction of the destruction of carbonates is very rapid:
CaCO3 + 2HCl → CaCl2 + H2O + CO2
After a day of infusion, the reaction of the solution is checked with litmus paper. If the reaction is acidic, the extract is filtered through a large folded filter. If the reaction is not acidic, add another 100-200 ml of titrated acid solution to the solution and insist again for a day, stirring periodically. 25 ml of the solution is taken from the filtered extract with a pipette, 2-3 drops of the methyl red indicator are added and the excess acid is titrated with a titrated alkali solution of the appropriate concentration (0.02, 0.1 or 0.2 n) until the red color turns pale yellow.
The amount of CO2 (%) is calculated by the formula
where a is the number of millimoles in 25 ml of the initial acid solution (i.e., the number of milliliters of HCl multiplied by the molar concentration of the solution); b is the number of millimoles in 25 ml of the extract (i.e., the number of milliliters of NaOH multiplied by the molar concentration); 0.044 is the gram value of the CO2 millimole; 100 is the coefficient conversion rate per 100 g of soil; K – conversion rate for dry soil; c - soil weight corresponding to 25 ml of extract.
To convert the percentage of CO2 carbonates into the percentage of CaCO3, the result obtained is multiplied by the coefficient 2.274.
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