Evaluation of the Methods Used for Carboxyhemoglobin Analysis in Postmortem Blood

Abstract

Numerous methods have been described in the literature for the determination of carboxyhemoglobin (COHb) in whole blood. The most popular and widely used have been (1) the spectrophotometric methods, which could be performed either by using a conventional spectrophotometer or by using specialized automated instruments known as CO-oximeters; (2) the gas chromatographic methods, with variable detection systems, which have been considered as the reference methods for every carbon monoxide analysis. The authors have critically reviewed previously reported comparative studies on these methods, considering statistical and analytical matters, in order to propose the best method for the determination of COHb in postmortem blood, that could be utilized in forensic toxicology laboratories where such analyses are limited in number (less than 20 per year). Criteria for evaluation have been accuracy, reliability, simplicity, time, and cost. The authors' concluding statement has been that the manual spectrophotometric method could be the method of choice for COHb determination in postmortem blood samples. It is simple, rapid, and reliable and fulfills the forensically acceptable accuracy. It is performed by the use of a conventional spectrophotometer, which is considered a basic instrument in every analytical laboratory.

Determination of Volatile Substances in Forensic Samples by Static Headspace Gas Chromatography

“…Due to the complexity of the above mentioned procedure, other calibration forms have been implemented, using certified gas standards (Czogala & Goniewicz, 2005) or the stoichiometric liberation of carbon monoxide from the reaction between formic acid and hot sulphuric acid (Cardeal, et al, 1993). Detection limits obtained by this technique are less than 0.1% of carboxyhemoglobin saturation in blood, which is much lower than the normal levels reported (Kunsman & Levine, 2003) and less than the detection limits of the spectrophotometric techniques, reported in 1% (Boumba & Vougiouklakis, 2005). Table 9 describes in detail, the chromatographic conditions for carbon monoxide determination by this technique.…”

“…Currently, the most widely used methods are those based on ultraviolet-visible spectrophotometry, utilizing conventional spectrophotometers, usually making two readings at two different wavelengths (Maehly, 1962) or by specialized spectrophotometers: oximeters (Mahoney, et al, 1993); these methods are fast and simple, however, they are unreliable in certain circumstances, such as in putrefied samples, where the putrefaction process produces substances that generate spectral interference or the spontaneous formation of methemoglobin and sulfhemoglobin, this way preventing the determination of carboxyhemoglobin, or in blood samples from fire deaths, where methemoglobin is spontaneously produced (Lewis, et al, 2004;Seto, 1994;Walch, et al, 1984). In this regard, static headspace gas chromatography is not affected by these circumstances, because this technique separates the carbon monoxide from blood, and is thus considered a highly specific and sensitive technique, which makes it the referential technique for determining carbon monoxide (Boumba & Vougiouklakis, 2005); however, static headspace gas chromatography has not been usually used for this type of analyses because it takes longer than established techniques and requires skilled personnel (Mahoney, et al, 1993). Nonetheless, that last disadvantage does not apply to forensic environments, where this technique is widely known.…”

“…These methods are based on colorimetry, infrared spectrophotometry, visible ultraviolet spectrophotometry and gas chromatography (Boumba & Vougiouklakis, 2005). Currently, the most widely used methods are those based on ultraviolet-visible spectrophotometry, utilizing conventional spectrophotometers, usually making two readings at two different wavelengths (Maehly, 1962) or by specialized spectrophotometers: oximeters (Mahoney, et al, 1993); these methods are fast and simple, however, they are unreliable in certain circumstances, such as in putrefied samples, where the putrefaction process produces substances that generate spectral interference or the spontaneous formation of methemoglobin and sulfhemoglobin, this way preventing the determination of carboxyhemoglobin, or in blood samples from fire deaths, where methemoglobin is spontaneously produced (Lewis, et al, 2004;Seto, 1994;Walch, et al, 1984).…”

“…This paper will review theoretical aspects of the static headspace technique, as well as complementary additions to it (Kolb, 1999;Slack et al, 2003), the most significant substances from the standpoint of forensic toxicology that can be analyzed by this technique as ethanol (Kugelberg & Jones, 2007;Macchia et al, 1994;Tagliaro et al, 1992), congeners of alcoholic beverages (Iffland & Jones, 2003), inhalants (Angerer & Horsch, 1992;Seto, 1994), anesthetics (Pihlainen & Ojanperä, 1998), carbon monoxide (Boumba & Vougiouklakis, 2005;Vreman et al, 1984) and cyanide (Calafat & Stanfill, 2002;Felby, 2009); in each case, the analytical conditions and modifications necessary for the equipment to perform each analysis will be exposed, advantages and disadvantages of this technique over other existing procedures will be discussed and also, issues relating to development of methods for this technique and their validation.…”

Accident or Arson: Is CO-Oximetry Reliable for Carboxyhemoglobin Measurement Postmortem?

“…The toxic effects of CO depend on the length of exposure, the concentration of CO gas, and ventilation. Short exposures to high CO concentrations, even greater than those typically associated with death, are often more survivable than exposures to more moderate concentrations over a prolonged period of time (2 ). Blood COHb concentrations Յ3% are found in nonsmokers, whereas smokers may have concentrations upwards of 10%-15%.…”