Bicarbonate Total Carbon Dioxide

Total carbon dioxide is used here to describe the quantity that is measured most often in automated analyzers by acidification of a serum or plasma sample and measurement of the carbon dioxide released by the process, or by alkaliniza-tion and measurement of total bicarbonate. Under certain conditions of collection and specimen handling, total carbon dioxide values determined in this manner may be almost identical with values for the calculated concentration of total carbon dioxide obtained in blood gas analysis (see later section in this chapter on blood gas methods). The patho- 

Methods for Determination of Serum or Plasma Total Carbon Dioxide 

One of the earliest methods for determining total CO2 was the manometric method for total CO2 content, using the Natelson microgasometer. This has been supplanted in clinical laboratories by automated methods. This method is described in some detail in an earlier edition of this text.  

Methods for total CO2 measurement in today s automated instruments are either electrode based or enzymatic. In indirect electrode-based methods, such as the Beckman Coulter Synchron and Dade Behring Dimension series of analyzers, the released gaseous CO2 after acidification is 

An enzymatic method for CO2 is illustrated by the methods used in the Abbott Aeroset, Bayer Advia, Roche Diagnostics Hitachi Modular, and most Ortho Diagnostics Virtos analyzers. The specimen is first alkalinized to convert aU CO2 and carbonic acid to HCO3. The enzymatic reactions are as follows  

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Various workers have discussed the determination of total alkalinity and carbonate [ 10-12], and the carbonate bicarbonate ratio [ 12] in seawater. A typical method utilises an autoanalyser. Total alkalinity (T milliequivelents per litre) is found by adding a known (excess) amount of hydrochloric acid and back titrating with sodium hydroxide solution a pH meter records directly and after differentiation is used to indicate the end-point. Total carbon dioxide (C milliequivelents per litre of HCO3 per litre) is determined by mixing the sample with dilute sulfuric acid and segmenting it with carbon dioxide-free air, so that the carbon dioxide in the sample is expelled into the air segments. The air... 

E551 O Leary, T.D. and Langton, S.R. (1989). Calculated bicarbonate or total carbon dioxide Clin. Chem. 35, 1697-1700. 

Total carbon dioxide (CO2) content of plasma consists of carbon dioxide dissolved in an aqueous solution (dCOa), CO2 loosely bound to amine groups in proteins (carbamino compounds), HCO3 and vanishingly small amounts of CO ions, and carbonic acid (H2CO3). Bicarbonate ions make up ail but 2 mmol/L of the total carbon dioxide of plasma (22 to 31 mmol/L). Measurement of the tota CO2 as part of an electrolyte profile is useful chiefly to evaluate HCO3 concentration in assessment of acid-base disorders. 

Manufacture. Aqueous sodium hydroxide, sodium bicarbonate, sodium carbonate, or sodium sulfite solution are treated with sulfur dioxide to produce sodium metabisulfite solution. In one operation, the mother Hquor from the previous batch is reinforced with additional sodium carbonate, which need not be totally in solution, and then is treated with sulfur dioxide (341,342). In some plants, the reaction is conducted in a series of two or more stainless steel vessels or columns in which the sulfur dioxide is passed countercurrent to the alkaH. The solution is cooled and the sodium metabisulfite is removed by centrifuging or filtration. Rapid drying, eg, in a stream-heated shelf dryer or a flash dryer, avoids excessive decomposition or oxidation to which moist sodium metabisulfite is susceptible. 

The natural supply source of carbon dioxide in MU water is primarily calcium bicarbonate alkalinity [Ca(HC03)2], which reacts under conditions of heat to form insoluble calcium carbonate and carbon dioxide. Because the precipitated carbonate cannot decompose further, no additional carbon dioxide is released. As a result, the total amount of... 

This second-stage decomposition reaction (carbonate hydrolysis) proceeds to approximately 80% completion at 150 psig, producing hydroxide alkalinity and carbon dioxide and providing a further 0.35 ppm carbon dioxide (80% of 0.44 ppm). Consequently, the total production of carbon dioxide from 1 ppm of bicarbonate alkalinity is 0.79 ppm at 150 psig. 

Vertical concentration profiles of (a) temperature, (b) potential density, (c) salinity, (d) O2, (e) % saturation of O2, (f) bicarbonate and TDIC, (g) carbonate alkalinity and total alkalinity, (h) pH, (i) carbonate, ( ) carbon dioxide and carbonic acid concentrations, and (k) carbonate-to-bicarbonate ion concentration ratio. Curves labeled f,p have been corrected for the effects of in-situ temperature and pressure on equilibrium speciation. Curves labeled t, 1 atm have been corrected for the in-situ temperature effect, but not for that caused by pressure. Data from 50°27.5 N, 176°13.8 W in the North Pacific Ocean on June 1966. Source From Culberson, C., and R. M. Pytkowicz (1968). Limnology and Oceanography, 13, 403-417. 

If heparin comprises 10% or more of the total volume of a sample for blood gas analysis, errors in measurements of carbon dioxide pressure, bicarbonate concentration, and base excess may occur. 

Infrared absorption in the atmosphere can have the same effect. Over the last century the concentration of carbon dioxide in the atmosphere has risen dramatically because of combustion. As a result, the atmosphere now absorbs more infrared radiation than it did in the past, and cooling into space is less efficient. A likely consequence is global warming, although a detailed calculation of the magnitude of the expected effect is far from simple. For example, while is it not difficult to estimate total CO2 emissions from combustion, most of these molecules end up in the ocean as carbonates or bicarbonates, and do not directly contribute to global warming. Nonetheless, there is broad consensus in the scientific community that carbon dioxide emissions will tend to increase the Earth s temperature over the next few decades, with environmental consequences which may be severe. 

Important is the conclusion that a significant amount of C02 may not be found in the exhaust gas but rather trapped in the culture liquid in the form of bicarbonate or even carbonate (in alkalophilic cultures). For example, Ponti [327] estimated that up to 25% of total carbon mineralized in sewage sludge treatment was captured as bicarbonate and not released via the gas phase. Disregarding this fact must result in systematically erroneous determinations of respiratory quotient (RQ), carbon dioxide production rate (CPR) and carbon recovery. However, taking all these factors into account allows the determination of the RQ-value, even in mammalian cell cultures, with reasonable accuracy even though bicarbonate and low gas turnover rates hamper the measurements [38]. 

The distinction between physical and chemical equilibrium is important. For example, when chlorine is absorbed into water, it first enters the water as dissolved chlorine and then undergoes a relatively slow chemical reaction with water to form HOCl, H", and Cl". Two equilibrium ratios may be written—one based on total chlorine in the liquid [CI2 + HOCl + Cl"], and the other based on dissolved CI2 only. It is the latter ratio which controls the mass transfer rate. As another example, when carbon dioxide is absorbed into alkaline aqueous solutions, it first dissolves as CO2 and then reacts with OH to form bicarbonate ion. The equilibrium ratio controlling the mass transfer rate is PC02/ [CO2]. This ratio is independent of pH and is aflFected only by changes in the ionic strength of the solution. The interphase equilibria of the reaction products are important only for reversible chemical reactions. 

Due to the dynamic equilibrium between the atmospheric carbon dioxide and the oceanic bicarbonate and carbonate anions, the greatest amount of soluble calcium cations is contained in the ocean. This mass is four orders of magnitude higher than the total mass of bound calcium in living and dead matter of both terrestrial and aquatic organisms. The average calcium content in the seawater is 408 mg/L, and the overall pool is 559 x lO tons. 

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