Sulfur dioxide sampling

Elemental sulfur (S) has been known since ancient times, its name coming from both Sanskrit (sulvere) and Latin (sulfurium). In 1808, a sulfur dioxide sample was burned to release the oxygen, but it was found to contain hydrogen as a contaminant. Eventually it was truly purified and was then verified to be an element as suggested by French chemist Antoine Lavoisier. 

Another important example of a redox titration for inorganic analytes, which is important in industrial labs, is the determination of water in nonaqueous solvents. The titrant for this analysis is known as the Karl Fischer reagent and consists of a mixture of iodine, sulfur dioxide, pyridine, and methanol. The concentration of pyridine is sufficiently large so that b and SO2 are complexed with the pyridine (py) as py b and py SO2. When added to a sample containing water, b is reduced to U, and SO2 is oxidized to SO3. 

Commercial boron trifluoride is usually approximately 99.5% pure. The common impurities are air, siUcon tetrafluoride, and sulfur dioxide. An excellent procedure for sampling and making a complete analysis of gaseous boron trifluoride has been developed (57). 

Sulfur dioxide concentrations as low as 40 mg/m in air have been determined bypassing air samples through an aqueous solution of tetrachloromercurate, which converts SO2 to the dichlorosulfitomercurate complex. Oxidation of the complex by potassium permanganate is chemiluminescent and the intensity, as measured by a photomultipHer, is proportional to sulfur dioxide concentration (312). 

Total sulfur in air, most of which is sulfur dioxide, can be measured by burning the sample in a hydrogen-rich flame and measuring the blue chemiluminescent emission from sulfur atom combination to excited S2 (313). Concentrations of about 0.01 ppm can be detected. 

Analytical Methods. The official NIOSH recommended method for determining sulfur dioxide in air consists of drawing a known prefiltered volume of air through a bubbler containing hydrogen peroxide, thus oxidising the sulfur dioxide to sulfuric acid. Isopropyl alcohol is then added to the contents in the bubbler and the pH of the sample is adjusted with dilute perchloric acid. The resultant solution is then titrated for sulfate with 0.005 M. barium perchlorate, and Thorin is used as the indicator. 

A method suitable for analysis of sulfur dioxide in ambient air and sensitive to 0.003—5 ppm involves aspirating a measured air sample through a solution of potassium or sodium tetrachloromercurate, with the resultant formation of a dichlorosulfitomercurate. Ethylenediaminetetraacetic acid (EDTA) disodium salt is added to this solution to complex heavy metals which can interfere by oxidation of the sulfur dioxide. The sample is also treated with 0.6 wt % sulfamic acid to destroy any nitrite anions. Then the sample is treated with formaldehyde and specially purified acid-bleached rosaniline containing phosphoric acid to control pH. This reacts with the dichlorosulfitomercurate to form an intensely colored rosaniline—methanesulfonic acid. The pH of the solution is adjusted to 1.6 0.1 with phosphoric acid, and the absorbance is read spectrophotometricaHy at 548 nm (273). 

The Reich test is used to estimate sulfur dioxide content of a gas by measuring the volume of gas required to decolorize a standard iodine solution (274). Equipment has been developed commercially for continuous monitoring of stack gas by measuring the near-ultraviolet absorption bands of sulfur dioxide (275—277). The deterrnination of sulfur dioxide in food is conducted by distilling the sulfur dioxide from the acidulated sample into a solution of hydrogen peroxide, foUowed by acidimetric titration of the sulfuric acid thus produced (278). Analytical methods for sulfur dioxide have been reviewed (279). 

Sulfur Dioxide EPA Method 6 is the reference method for determining emissions of sulfur dioxide (SO9) from stationary sources. As the gas goes through the sampling apparatus (see Fig. 25-33), the sulfuric acid mist and sulfur trioxide are removed, the SO9 is removed by a chemical reaction with a hydrogen peroxide solution, and, finally, the sample gas volume is measured. Upon completion of the rim, the sulfuric acid mist and sulfur trioxide are discarded, and the collected material containing the SO9 is recovered for analysis at the laboratory. The concentration of SO9 in the sample is determined by a titration method. 

EPA Method 6C is the instrumental analyzer procedure used to determine sulfur dioxide emissions from stationaiy sources (see Fig. 25-30). An integrated continuous gas sample is extracted from the test location, and a portion of the sample is conveyed to an instrumental analyzer for determination of SO9 gas concentration using an ultraviolet ( UV), nondispersive infrared (NDIR), or fluorescence analyzer. The sample gas is conditioned prior to introduction to the gas analyzer by removing particulate matter and moisture. Sampling is conducted at a constant rate for the entire test rim. 

Smoke concentrations ranged from 0.3 to more than 4 mg m . Daily means of the sampling stations are shown in Fig. 18-4. Sulfur dioxide measurements ranged from less than 0.1 ppm (260 /rg m ) to 1.34 ppm (3484 /Ag m" ). Also, 4 of the 11 stahons had at least one daily value in excess of 1 ppm, and 9 of the 11 stations had at least one daily value in excess... 

From Fig. 21-10, what wind directions are related to highest average winter sulfur dioxide concentrations at this sampling station ... 

Consider coal burning in a boiler house. The assessor may not be able to measure the mass of sulfur dioxide (SOj) leaving the boiler stack, because of access problems and the lack of suitable sampling ports on the stack. The only information available is that the coal is of soft quality, containing 3% sulfur by weight and, on average, 1,000 kg of coal is burned each day. 

The sulfur dioxide analyzer based on the ultraviolet principle is a sensitive instrument. Its detection limit can be less than one ppbv (parts per billion by volume). When used in emission measurements, the sample gas IS normally diluted prior to the measurement using a diluting stack sampler. 

Determining the sulfur content in crudes is important because the amount of sulfur indicates the type of treatment required for the distillates. To determine sulfur content, a weighed crude sample (or fraction) is burned in an air stream. All sulfur compounds are oxidized to sulfur dioxide, which is further oxidized to sulfur trioxide and finally titrated with a standard alkali. 

At 25°C and 380 mm Hg, the density of sulfur dioxide is 1.31 g/L. The rate of effusion of sulfur dioxide through an orifice is 4.48 mL/s. What is the density of a sample of gas that effuses through an identical orifice at the rate of 6.78 mL/s under the same conditions What is the molar mass of the gas ... 

Fig. 7-2 Vertical profiles of physical (temperature, dew point, and backscatter coefficient) and chemical (ozone, sulfur dioxide) variables near Scranton, PA during the afternoon of 20 July 1978. (Modified with permission from P. K. Mueller and G. M. Hidy (1982). "The Sulfate Regional Documentation of SURE Sampling Sites", EPRI report EA-1901, v. 3, Electric Power Research Institute.)...

C03-0134. A sulfur-containing ore of copper releases sulfur dioxide when heated in air. A 5.26-g sample of the ore releases 2.12 g of SO2 on heating. Assuming that the ore contains only copper and sulfur, what is the empirical formula ... 

This is one source of acid rain, a serious environmental problem. The sulfur dioxide content of an air sample can be determined. A sample of air is bubbled through an aqueous solution of hydrogen peroxide to convert all of the SO2 to H2 SO4. H2 O2 + SO2 H2 SO4 Titration of the resulting solution completes the analysis (both H atoms of H2 SO4 are titrated). In one such case, the analysis of 1.55 X 10 Lof Los Angeles air gave a solution that required 5.70 mL of 5.96 X 10 M NaOH to complete the titration. Determine the number of grams of SO2 present in the air sample. 

NIOSH (method 6013) describes the measurement of hydrogen sulfide in the air by ion chromatography (NIOSH 1994b). This method has a working range of 0.9-20 mg/m3 for a 20-L air sample and an estimated limit of detection of 11 g per sample. However, sulfur dioxide may interfere with the measurement of hydrogen sulfide. 

The Iodometric method has also been utilized in analyzing hydrogen sulfide in the air (EPA 1978). The method is based on the oxidation of hydrogen sulfide by absorption of the gas sample in an impinger containing a standardized solution of iodine and potassium iodide. This solution will also oxidize sulfur dioxide. The Iodometric method is suitable for occupational settings. The accuracy of the method is approximately 0.50 ppm hydrogen sulfide for a 30-L air sample (EPA 1978). 

It is roughly estimated that there are more than 1,200,000 water bodies in eastern North America that are currently affected by acid deposition. A subset of these lakes has been sampled since early 1980s in order to monitor the changes in lake water chemistry induced by the declining sulfur dioxide emissions and wet sulfate deposition... 

The Karl Fischer method is a titration to determine the water content in liquid and solid materials. The method utilizes a rather complex reaction in which the water in a sample is reacted with a solution of iodine, methanol, sulfur dioxide, and an organic base ... 

Oxidative microcoulometry has become a widely accepted technique for the determination of low concentrations of sulfur in petroleum and petroleum products (ASTM D3120). The method involves combustion of the sample in an oxygen-rich atmosphere followed by microcoulometric generation of a triiodide ion to consume the resulting sulfur dioxide. It is intended to distinguish the technique from reductive microcoulometry, which converts sulfur in the sample to hydrogen sulflde that is titrated with coulometrically generated silver ion. 

The bomb method for sulfur determination (ASTM D129) uses sample combustion in oxygen and conversion of the sulfur to barium sulfate, which is determined by mass. This method is suitable for samples containing 0.1 to 5.0% w/w sulfur and can be used for most low-volatility petroleum products. Elements that produce residues insoluble in hydrochloric acid interfere with this method this includes aluminum, calcium, iron, lead, and silicon, plus minerals such as asbestos, mica, and silica, and an alternative method (ASTM D1552) is preferred. This method describes three procedures the sample is first pyrolyzed in either an induction furnace or a resistance furnace the sulfur is then converted to sulfur dioxide, and the sulfur dioxide is either titrated with potassium iodate-starch reagent or is analyzed by infrared spectroscopy. This method is generally suitable for samples containing from 0.06 to 8.0% w/w sulfur that distill at temperatures above 177°C (351°F). 

In the iodate detection system (ASTM D1552), the sample is burned in a stream of oxygen at a sufficiently high temperature to convert about 97% by weight of the sulfur to sulfur dioxide. The combustion products are passed into an absorber containing an acidic solution of potassium iodide and starch indicator. A faint blue color is developed in the absorber solution by the addition of standard potassium iodate solution. As combustion proceeds, bleaching the blue color, more iodate is added. The sulfur content of the sample is calculated from the amount of standard iodate consumed during the combustion. 

In the infrared detection system, the sample is weighed into a special ceramic boat which is then placed into a combustion furnace at 1371°C (2500°F) in an oxygen atmosphere. Most of the sulfur present is converted to sulfur dioxide, which is then measured with an infrared detector after moisture and dust are removed by traps. The calibration factor is determined using standards approximating the material to be analyzed. 

Karl Fischer reagent analy chem A solution of 8 moles pyridine to 2 moles sulfur dioxide, with the addition of about 15 moles methanol and then 1 mole iodine used to determine trace quantities of water by titration. karl fish-or re a-jont Karl Fischer technique analy chem A method of determining trace quantities of water by titration the Karl Fischer reagent is added in small increments to a glass flask containing the sample until the color changes from yellow to brown or a change in potential is observed at the end point. karl fish-or tek nek kauri-butanol value analychem The measure of milliliters of paint or varnish petroleum thinner needed to cause cloudiness in a solution of kauri gum in butyl alcohol. kail-re byut-3n,ol, val-yu ... 

Sulfur dioxide in the sample causes a negative interference of approximately 1 mole of ozone per mole of sulfur dioxide, because it reduces the iodine formed by ozone back to potassium iodide. When sulfur dioxide concentrations do not exceed those of the oxidants, a method commonly used to correct for its interference is to add the amount of sulfur dioxide determined by an independent method to the total detector response. A second method is to remove the sulfur dioxide from the sample stream with solid or liquid chromium trioxide scrubbers. Because the data on the performance or these sulfur dioxide scrubbers are inadequate, the performance for each oxidant system must be established experimentally. 

There are several potential sources of error in these methods. The filters routinely used have a relatively high and somewhat variable sulfate content, so that, at concentrations lower than 10 Mg/m and sampling periods less than 24 h, the reliability of tlie sulfate measurement is reduc. Several different types of filtering media adsorb sulfur dioxide during the ftrst few hours of sampling this alters the amount of sulfate observed. This interference can become critical when sampling periods are less than 24 h and the concentration ratio of sulfur dioxide to sulfate is greater than 5 1. Interference can also be introduced by hot-water extraction when reduced sulfur compounds like sulfite are present, because they are oxidized to sulfates in this process. Another possible error source is that some of the various analytic procedures us for sulfate determination may be influenced by other substances also present in the particulate matter. 

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