Drugs and Poisons in Humans - A Handbook of Practical Analysis (Part 10)

Introduction:The incidence of carbon monoxide (CO) poisoning is highest among those of various poisonings in forensic science practice; about 2/3 of the total accidental poisoning deaths is due to CO poisoning in Japan [1]. Previously, suicides, homicides and accidental deaths frequently took place using city gas containing about 9% CO. However, during recent years, city gas is being replaced by natural gas containing no CO, resulting in drastic decrease of the number of CO poisoning cases. Nevertheless, many incidents of CO poisoning are occurring due to imperfect combustion, fire, exhaust gas of automobiles and other causes. For a victim...
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Drugs and Poisons in Humans - A Handbook of Practical Analysis (Part 10)II. Chapters on specific toxins 1.1II.1.1 Carbon monoxide By Keizo SatoIntroductionThe incidence of carbon monoxide (CO) poisoning is highest among those of various poison-ings in forensic science practice; about 2/3 of the total accidental poisoning deaths is due to COpoisoning in Japan [1]. Previously, suicides, homicides and accidental deaths frequently tookplace using city gas containing about 9% CO. However, during recent years, city gas is beingreplaced by natural gas containing no CO, resulting in drastic decrease of the number of COpoisoning cases. Nevertheless, many incidents of CO poisoning are occurring due to imperfectcombustion, fire, exhaust gas of automobiles and other causes. For a victim found at the sceneof a fire, the saturation ratio of carboxyhemoglobin (COHb) can be an indicatora for judgingwhether the victim has died in a fire or had been already killed before the fire. For measurements of COHb saturation ratios in blood, spectrophotometric and GC meth-ods are available. Since methemoglobin (Met-Hb) is contained in many of blood specimens inforensic science practice for measurements of COHb saturation [2], it is important to use amethodb, which is not influenced by the presence of Met-Hb. In this chapter, simple and reli-able spectrophotometric [3] and GC [4] methods for measurements of COHb saturation not tobe influenced by Met-Hb are presented.Spectrophotometric methodSee [3].Reagents and their preparation• 0.1% Na2CO3 solution: 0.1 g Na2CO3 is dissolved in distilled water to prepare 100 mL solu- tion.• 5 M NaOH solution: 20 g NaOH is dissolved in distilled water to prepare 100 mL solu- tion.• Sodium hydrosulfite (sodium dithionite) obtainable from Yoneyama Yakuhin Kogyo Co., Osaka and other manufacturers.Analytical instrumentA Hitachi 557 dual-wavelength spectrophotometer (Hitachi, Ltd., Tokyo, Japan)© Springer-Verlag Berlin Heidelberg 200592 Carbon monoxide Procedure i. Two 3-ml volume cuvettes of the same type are cleaned well by washing with distilled water. ii. A 2.5-mL volume of 0.1% Na2CO3 aqueous solution is placed in a cuvette. iii. About 2 mg of solid sodium hydrosulfite is added to the above cuvette and mixed well. iv. A 10-µL volume of whole blood and 0.2 ml of 5 M NaOH solution are added to the mixture and mixed well. v. After standing for 5 min, the absorbances at 532 and 558 nm (A532 and A558) are read against distilled water in another cuvette as a blank. vi. The percentage of HbCO can be calculated by the following equation: COHb %=(2.44–A558/A532) × 67 Assessment and some comments on the method The above spectrophotometric assay for HbCO saturation ratio well meets the needs in forensic science practice. To perform accurate measurements of low ranges of COHb by this method, the following modification of the method is recommended. About 20–30 specimens of fresh blood obtained from healthy subjects is analyzed accord- ing to the above procedure. A specimen with the lowest COHb value is taken as 0%, which can be used as the blank test. When the blood specimen with the lowest COHb value is processed through 1–4 described in the above procedure, the absorbance spectrum 1 due to reduced Hb can be obtained as shown in > Figure 1.1; when CO gas is then bubbled in the same cuvette, the absorbance spectrum 2 shown in the same figure can be obtained. In the spectrum 1, the isobestic point around 532 nm and the absorbance maximum around 558 nm appear; the exact wavelengths are re-examined for both points and small shifts of their wavelengths according to instrumental conditions can be corrected. Even when the absorptions at corrected wavelengths ⊡ Figure 1.1 Absorption spectra of reduced Hb (1) and COHb (2) in the presence of NaOH. GC analysis 93are used, it is not necessary to change the coefficient values in the above equation. The methodusing a blank test of a healthy and fresh blood and using corrected wavelengths enables theaccurate measurements of COHb contents less than 10% [3, 5]. For measurements of COHb in bloody fluids in the thoracic and abdominal cavities, aspecial care should be taken. Kojima et al. [6] reported that 2.3–44.1% of COHb could be de-tected from bloody fluids in the thoracic cavities of 7 victims without any fire or CO exposure,while COHb contents in the hearts were only 0.3–6.0%. The high COHb contents found in thethoracic fluids are considered due to postmortem product ...