Analysis of Hydrogen Sulphide - Essay Example

Analysis of Hydrogen Sulphide Name Course Lecturer Date Introduction The aim of this paper is to describe the analytical techniques that have been discovered that can help in the detection, monitoring, and measurement of hydrogen sulfide, together with its metabolites, as biomarkers in cardiovascular system. The intention of this paper is not to offer an extensive list of bioanalytical techniques. Instead, the main intention is to select well-established methods or techniques that can be employed as the standard bioanalytical methods as far as the detection of hydrogen sulfide in the cardiovascular system is concerned. It is important to note that majority of the bioanalytical methods employed for detection of the contents of environmental samples are those that the federal organizations and agencies such as the National Institute for Occupational Safety and Health, otherwise abbreviated as NIOSH, and EPA have approved. Some of the bionalytical methods that this paper will present will include those that have been approved by such groups as the American Public Health Association, abbreviated as APHA and Association of Official Analytical Chemists, abbreviated as AOAC. Biological Samples A small number of analytical methods have been employed in detecting the amounts of hydrogen sulfide in such samples as the expired air or breath. The methods for detecting sulfide in such biological fluids and tissues as saliva and blood are also limited. However, the methods for carrying out these investigations or detections include the use of gas chromatography in combination with a number of other methods. Such combinations will include gas chromatography and flame ionization detection or gas chromatography in combination with flame photometric detection. The other bioanalytic methods include potentiometry using ion-selective electrodes, iodometric titration, high performance liquid chromatography, abbreviated as HPLC, and spectrophotometry. Because of the volatility of hydrogen sulfide, it is difficult to measure its concentration in biological materials. The other challenges in measuring the concentration of hydrogen sulfide are that it has a tendency of undergoing oxidation, it can be adsorbed to rubber, or glass and it can bind to organic molecules. In the atmosphere, hydrogen sulfide is found or exists in molecular form. There are techniques that are available for measuring hydrogen sulfide in atmosphere. However, when it is in aqueous solution, this substance exists as a weak acid. In this case, it exhibits 2 acid dissociation constants. The first dissociation constant produces bisulfide ions, in other words, (HS-). The second dissociation produces sulfide ion, in other words, S2-. Each of these dissociations has pK values of 7.04 and 11.96. In biological fluids and tissues, it is very possible to determine the concentrations of hydrogen sulfide. In order to calculate the concentration of hydrogen sulfide that is un-ionized, one uses the concentration of sulfide that is dissolved. The body tissue found in the cardiovascular system is mainly blood. The biolanalytical methods that will be used to detect the presence of hydrogen sulfide in blood will be iodometric method and potentiometry method. Identity and chemical/physical properties The other name for hydrogen sulfide (H2S is hydrosulfuric acid, dihydrogen monosulfide, sulfurated hydrogen, sulfur hydride, stink damp, hepatic gas, hydrogen sulfuric acid, sewer gas, and dihydrogen sulfide. The illustration of its structural formula is H-S-H. it is a colorless gas that is also flammable. Its characteristic odor is like that of rotten eggs. The relative molecular mass for hydrogen sulfide is 34.08. it has a vapor pressure of 1929 Pa at 21.90C. The gas can dissolve in water. It has a solubility of 1g in 242 ml in water at 200C. the hydrogen sulfide taste threshold in water ranges between 0.1 mg/litre and 0.05 mg/litre. Apart from being soluble in water, hydrogen sulfide is also soluble in carbon disulfide, crude oil, kerosene, gasoline, glycerol, ether. Analytical methods Sample preparation Female and male Sprague-Dawley rats with body weights ranging from 250 and 350 g are used in this method of analyzing hydrogen sulphide amounts in aortal blood. There is the induction of anesthesia with intraperitoneal injection of xylazine and ketamine, which measure 16 and 100 mg/kg, respectively. The next thing is to excise the thoracic aortas immediately. The thoracic aortas are place in a buffer called Krebs-Henseleit (K-H), which is at a PH of 7.3 at 370C. This buffer has 50-μM diethylenetriaminepentaacetic acid (DTPA). The role of this acid is to chelate trace metals found in the solution that play a role of catalyzing the oxidation of hydrogen sulfide (H2S). The next step is to clean aorta segments of blood and adventitious tissue before cutting them into eight or seven segments that are approximately 3 mm long. The tail artery is also excised. This excised tail artery is sectioned to form segments that are 3 mm long. These sections are used to assess the oxygen dependence of peripheral artery through respirometric experiments. In such biological samples as biological fluids and tissues like saliva and blood as well as the human breath, hydrogen sulfide can be determined using a number of methods that are commonly used. Among these methods are high-performance liquid chromatography,abbreviated as HPLC, spectrophotometry, potentiometry with the use of ion-selective electrodes, iodometric titration, gas chromatography combined with flame ionization detection. The methods that are mainly used in measuring hydrogen sulfide samples in such environmental samples as sludge, sediment, water, and air include gas chromatography combined with flame photometric detection, gas chromatography combined with electrochemical detection, methylene blues colorimetric, iodometric methods, and spectrophotometric method. A selective method, which is also dynamic, can determine the presence of sulphide in solid and liquid samples. This method bases its determination on the integration of potentiometric sulphide monitoring and hydrogen sulphide pervaporation in a module that is made in the laboratory. This method involves the conversion of the analyte into hydrogen sulfide. This is done by reacting it with a stream that is acid donor. After the process of pervaporation, this analyte is accepted into a dilute solution of NaOH. The determination rate of the method produced ranges between 0.3–50 μg g−1 and 0.1–30 μg ml−1 for solid and liquid samples, respectively. The precision of this method, as expressed in form of standard deviation is 4.3 and 3.1%, respectively. Hydrogen sulfide has been seen as a toxic gas for a long time. The same gas can however, be used in mammals as an endogenous signaling substance. This recognition of hydrogen sulfide as a signaling substance places a lot of emphasis on the substance’s pathological and physiological pathways as seen in the body’s cardiovascular system. Consequently,  the hydrogen sulfide gas in biological fluids is a weak acid. Its existence has approximately 85% HS(-) and 15% H(2)S with a trace of S(2-). The reference of the mixture in this case is "H(2)S" consequently, H(2)S has been discovered to have huge influence in the contractile functions of the heart. The substance may play a big role as a cardioprotectant during which it can be used to treat heart failure and ischemic heart diseases. Changes in the level of endogenous hydrogen sulfide have been discovered in animal models with different pathological conditions like spontaneous hypertension, hypoxic pulmonary hypertension, and myocardial ischemia. Recent reports have revealed that H2S plays a key role of modulating vascular responses directly. When H2S is administered through intravascular means, it causes a clear depression of average blood pressure. This depression is not linked to a reduction in heart rate. The fact that H2S has a potential physiological role in vascular function can be supported by the fact that rats, which have spontaneous hypertension show elevated blood pressure that is chronic. The serum H2S levels of these rats are half of those for control levels. However, when NaHS is injected into the rates, the 50, 55 conditions can be reversed. Besides, the H2S levels of the serum are elevated during endotoxic or septic shock. It is noted that perhaps it is because of this elevation that the blood pressure drops. Strips or rings of uterine smooth muscle or vascular smooth muscle that are exposed to NAHS solution show a reduction in tension. While data from research is supporting a function of H2S when it comes to the modulation of vascular function, chances are high that these amounts of H2S can be found in vivo. H2S Measurement The concentration of H2S in the vessel organ bath or in respirometer chamber is recorded using a PHSS that is connected to an analyzer that is multichannel. The PHSS used in this case, displays selectivity for H2S and responds fast to changing concentrations of H2S. It however has a lower limit of detection that is near 10Nm. In each experimental chamber, the PHSS calibrations are made. These calibrations are made by the use of anoxic stock solutions. These anoxic solutions made on daily basis as 10mm H2S in a potassium phosphate buffer of 50mm. the stock solutions ensures that there is no need of using special apparatus for handling the pure H2S gas. Recently, the hydrogen sulfide has been found to play a role as far as mammalian cell signaling is concerned. Hydrogen sulfide is produced in most of the tissues. It has been detected in brain and blood in micromolar quantities. In physiological solution, H2S exists in equilibrium as H2S ↔ H+ + HS− in reaction 1 and ↔ H+ + S2− in reaction 2. This equilibrium is obtained with pK values being 14 and 6.9 for reactions 2 and 1 respectively, while the concentrations of HS- and H2S represent approximately 70% and 30% respectively, of the total sulfide. The concentration of S-2 on the other hand is negligible. Polarographic H2S Sensor In summary, out of all the analytical methods discussed it is polarographic H2S Sensor (PHSS) as discussed above that is more effective in detecting H2S in aortic blood samples. The invention of the polarographic H2S sensor (PHSS) was done in 2005. It was developed as a voltammetry, which had cathode, anode, and electrolyte that an H2S permeable polymer membrane protected it from solution constituents. The PHSS has been applied as an analytical method at organ, tissue and cellular levels. The method has demonstrated, at the nanomolar range, high sensitivity. The response time to H2S has also been rapid. It has been possible to achieve real-time detection of levels of O2 and H2S in vessel tension and respirometry experiments with this PHSS method. The dimensions of most of the PHSS are similar to those of polarographic oxygen sensor. Read More