An environmental study was performed to measure the transport of a DDT (a banned pesticide) throughout the globe. A lake in northern Canada was sampled to see if low levels of DDT were present there in spite of it not being administered within 1000 miles of that location. 1.000 L of the lake water was spiked with 100.0 uL of a 2.451 ug/L solution of tetrachlorobenzene, which acted as the internal standard. The entire 1.000 L spiked solution was concentrated onto an SPE column. After washing the SPE column with ~5 mL of pure water, the analyte and internal standard were eluted from the SPE column using ~5 mL of CH2Cl2 solvent. The eluted sample was evaporated under a stream of nitrogen to a final volume of 1.000 mL. 1 uL of this final solution was analyzed using GC-MS, and gave a signal of 24835 for DDT and 11597 for tetrachlorobenzene. To calculate the response factor, a standard solution was prepared consisting of 1.482 ug/L of DDT and 2.451 ug/L of tetrachlorobenzene. Analysis of this standard on the GC-MS resulted in signals of 269466 for DDT and 150899 for tetrachlorobenzene.
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
- An environmental study was performed to measure the transport of a DDT (a banned pesticide) throughout the globe. A lake in northern Canada was sampled to see if low levels of DDT were present there in spite of it not being administered within 1000 miles of that location. 1.000 L of the lake water was spiked with 100.0 uL of a 2.451 ug/L solution of tetrachlorobenzene, which acted as the internal standard. The entire 1.000 L spiked solution was concentrated onto an SPE column. After washing the SPE column with ~5 mL of pure water, the analyte and internal standard were eluted from the SPE column using ~5 mL of CH2Cl2 solvent. The eluted sample was evaporated under a stream of nitrogen to a final volume of 1.000 mL. 1 uL of this final solution was analyzed using GC-MS, and gave a signal of 24835 for DDT and 11597 for tetrachlorobenzene. To calculate the response factor, a standard solution was prepared consisting of 1.482 ug/L of DDT and 2.451 ug/L of tetrachlorobenzene. Analysis of this standard on the GC-MS resulted in signals of 269466 for DDT and 150899 for tetrachlorobenzene.
a. Calculate the relative response factor for this measurement (see Equation 1)
b. Calculate the concentration of DDT in the concentrated sample analyzed in ug/mL
(hint, what is the concentration of the tetrachlorobenzene in this sample?)
c. Calculate the concentration of DDT in the lake water sample in ug/L.
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