Dissolved Carbon Monoxide Measurements

Dissolved CO concentrations can be determined using a myoglobin-protein assay as described by Kundu et al. (2003). This method was used by Riggs and Heindel (2006), Kapic et al. (2006), and Ungerman and Heindel (2007) to determine pure CO concentrations in water to assess CO-water mass transfer rates for various operating conditions. A sununary of the bioassay measurement technique is provided next and further details can be found in Jones (2007). 

1 Bioassay Overview. In the bioassay, a liquid sample is taken from the bioreactor and the dissolved carbon monoxide concentration is determined off-line using a protein-binding method. The use of the bioassay is limited, much like the 

As with any analytical method, the success of the bioassay is highly dependent on how the samples are collected and prepared. Care must be taken during all of the steps of the analysis to ensure that oxygen is not allowed to bind with myoglobin and that all measurements are carried out very carefully. Furthermore, attention to sample acquisition must be taken to ensure that small gas bubbles are not entrained in the samples when they are collected as this leads to errors (Kapic, 2005). Although difficult to use, the bioassay technique, once mastered, may be successfully used to accurately measure dissolved carbon monoxide concentrations. 

The concentration is determined by putting 1 ml of buffer solution into a cuvette and adding 1 p/ of myoglobin protein. The absorbance is measured and more protein is added in 1 p/ increments until the peak absorbance is near 1.5. 

Once the peak absorbance reaches Abs 1.5, the myoglobin concentration (Cp) and the dilntion ratio (DR) are determined from 

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The liquid samples are analyzed after the three reference spectrums have been determined. After 1 ml of test solution has been placed in the cuvette, a 10 p/ liquid sample is injected into the cuvette and the cuvette is capped, gently agitated, and then scanned. This process is repeated for each of the acquired liquid samples. The resulting spectra will follow the trend shown in Figure 4.11, where an increase in the amount of dissolved carbon monoxide results in the peaks of the spectra initially shifting down and to the left and then up and to the left. Errors may occur in these measurements because of gas bubbles becoming entrained in the liquid sample when it is drawn thus, care must be taken to ensure that the syringes are clean and properly located in the sample port. 

The vapor-liquid equilibrium relationships for copper-ammonium salt solutions containing dissolved carbon monoxide have been studied by a number of investigators. Hainsworth and Titus (1921) measured the vapor pressure of carbon monoxide over copper-ammonium carbonate solutions. Experimental data on formate solutions were obtained by Larson and Teitsworth (1922). Zhavoronkov and Reshchikov (1933) studied solutions of chlorides, formates, lactates, and acetates. Zhavoronkov and Chagunava (1940) made a detailed study of formate-carbonate mixtures, including the solution from an operating plant. 

For photolysis of the ethylene—carbon monoxide copolymer in solution, the AH-6 lamp and a 20-mm. path-length quartz cell were used. The cell was filled with the solvent, pure n-heptane, and the intensity of the lamp was measured at the experimental temperature. Freeze-dried polymer was then added to make a 2% solution, which absorbed about 25% of the light. The polymer was dissolved, and the solution was mixed by a dry nitrogen stream, which also flushed out any air dissolved in the solvent. The light beam was then allowed to enter the cell, and the photolysis commenced the intensity of the emergent beam was monitored by the photomultiplier tube and the recorder. At the end of the photolysis the cell was filled with pure solvent, and the intensity of the lamp was measured again. The polymer was recovered from solution by evaporating the heptane it was then dissolved in benzene and freeze-dried. 

The majority of methods for the continuous optical monitoring of gases can be divided into two groups. In the flrst, the intrinsic optical property of the gas is exploited to sense it. lypical examples include chlorine, methane, carbon monoxide, and nitrogen oxides. In the second method, an indicator is used to transduce the gas concentration into a measurable optical parameter. This approach has frequently been applied when the gas has no useful intrinsic optical property or when it is dissolved in water. Typical examples include oxygen, carbon dioxide, and sulfur dioxide. 

Figure 8,1 Periodic bursts of carbon monoxide observed when methanoic acid is dissolved in a concentrated solution of sulfuric acid at 55 C. The vertical axis represents a rate of CO liberation measured in arbitrary units.

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