Inhalants Toluene - Research Paper Example

Unit: Toluene identification and quantification Toluene is a component that is found in glue, gasoline and paint products. Itis also found in small proportion in nail polish and other similar polish. The vapor is commonly used as an inhalant that causes intoxication greater than that of most other inhalants. Toluene is a clear, insoluble liquid. It is a substituted benzene derivative. It is an aromatic hydrocarbon commonly used for livestock and as a solvent. To test the presence of Toluene, different analytical methods are used, to identify and quantify the presence of Toluene. This paper discusses three analytical methods that can be used to test the presence of toluene in any substance. Toluene can be difficult to identify especially without any chemical tests since it smells like most other hydrocarbons and most people might pass it for any ordinary hydrocarbon. Like other hydrocarbons, toluene is soluble in organic solvents and does not dissolve in any polar solvent such as water. Therefore, to test its presence using chromatography, t has to be dissolved in an inorganic solvent. This way, it can be able to be separated by chromatography. This allows it to be tested from other substances including blood to check if someone has inhaled it. Gas Chromatography GC This is a physical separation technique for separating volatile mixtures. It is practiced in areas such as pharmaceuticals, environmental conservation and cosmetics. Due to their volatility, human breath, secretions, and other body fluids can be analyzed using this technique. It can also analyze air samples for various compounds. This is one of the analytical methods that are used to test toluene. This technique came up in early 60s. Among the various forms of GC, gas-liquid chromatography is the most popular method. Combined with techniques such as mass spectrometry, it becomes invaluable to separation and identification of molecules. This technique has been applied in the separation of toluene from other compounds for a very long time. Various kinds of detectors can be used to separate toluene and the other components in the substance. They include flame ionization detector, thermal conductivity detector and electron capture detector. Factors influencing the separation process include the stationary phase’s polarity. The polar compounds have strong interactions during this phase. This causes polar compounds to have a longer retention times than their non-polar counterparts. The temperature also affects the process by reducing the retention time. How to identify and quantify toluene using gas chromatography Chromatographic detectors react differently to each compound. To determine quantitative amounts of a variety of compounds in a separation mixture, the detector response should be calibrated in standards. Standard solutions of the sample are usually injected and the detector response recorded. Comparison of the sample retention and standard times allows the sample`s qualitative analysis. The peak area can be determined by carefully cutting out the peak or by measuring it directly on the chart recorder output with a planimeter and weighing it on an analytical balance. Chromatographic integrators that calculate the area could also be used. Apparatus Gas chromatograph with a thermal conductivity detector Temperature monitors and digital flow meter. Digital balance Computer acquisition of data with peak integration program. Instrument setting Flow rate :60mL/minute Temperature setting:75 degrees Celsius Attenuation should be as required. Column: L ×1/4 inch DNP. Procedure Make 1 ml injections of each of pure methylene chloride, cyclohexane, and toluene. Measure retention times of all. Measure peak areas of each through the cut-and-weigh method or directly with a chromatographic integrator. Prepare approximately 5 ml of a 1:1:1 by weight solution of methylene chloride, cyclohexane and toluene using a pipette and a digital balance. Inject a 1 ml of the mix. Prepare four separate mixtures of toluene and cyclohexane, using same amounts of cyclohexane but varying the amount of toluene, about .25:2, .5.2, .75:2, and 1:1 toluene to cyclohexane. Inject 1 ml of each. Get a toluene unknown mixture then makes a 1 ml injection to determine the amount of toluene relative to cyclohexane. Calculations Calculate the number of theoretical plates for methylene chloride, cyclohexane and toluene at 60 ml/min flow. Determine detector response for methylene chloride and toluene relative to cyclohexane as a ratio of peak areas. Determine the peak area ratio for each standard mixture using either the automatic integrator. Plot the curve. Plot a calibration curve, determine a linear conversion factor for converting peak area to concentration in mg/g depending on the relationship between peak area and toluene standard solution concentration, and determine the concentration of toluene in the unknown based on the calibration step. An injection port can also be used to identify and quantify toluene. It has a rubber cork through which the sample substances are injected. This means that the substances to be tested have to be in solid form it has to be dissolved using an appropriate solvent. The point of injection has to be maintained at a higher temperature than the boiling point of the most volatile component of the mixture (Harris 231). The injector could be either a normal packed column injector or a split column injector. For a normal packed injector, the process starts with the injection of a small amount of the liquid using a syringe. It has to be kept hot so that it vaporizes the liquid sample. The vapor is pushed into the column by a high-pressure inert gas. To keep the injector hot, a thermostatically controlled large metal block is used. Below is a figure of the packed column injector. High performance liquid chromatography (HPLC) HPLC works in a similar way to techniques such as column and layer chromatography. The difference is that rather than the solvent being passed through a column under the effects of gravitational pull, a force of up to 400 atmospheres is applied to it to make the process faster (L. R. Snyder 567). The method also allows one to use small particles in packing material for the column. This effectively increases the surface area for separation of components. The detection methods used are also more sensitive. In the test and quantification of toluene, this test is faster and convenient compared to the use of GC. It also requires that the substance to be tested be in liquid state. Specifications Column dimensions are typically an internal diameter of 4.66mm, the length of 250mm. The columns are shorter because they generate lower backpressure, allowing the user the flexibility of adjusting the flow rate. Particle size is the next specification. Columns are stacked with silica particles, with the size ranging between 3 and 5 microns. Larger particles generate less pressure within the system. The smaller ones generate more pressure resulting in more efficiency in separation (J.J. Kirkland 571). The stationary phase is the next component of the system. It is made of alkyl chains. C4, C8 and C18 are the common chain lengths for this component. How to use high liquid chromatography to measure toluene Method: Mix 1 ml of the sample with an equal volume of acetonitrile in a 2.2 ml HPLC glass bottle. Seal the bottle tightly and store in a store at a degrees Celsius. Add 100-microl methanol to the mixture to prevent confounding effects of glycosuria immediately before HPLC determination. Spin the bottle to remove any suspended matter. Introduce an aliquot of the supernate into the HPLC system and analyze on a PRODIGY column with an acetonitrile water mixture to serve as the mobile phase. Monitor the effluent at 191nm. Determine the retention times to identify the toluene and draw a calibration curve of the analyte concentration for quantitative analysis. Retention time This is the time it takes toluene to travel from the injection point to the detector from where it is detected. It is taken when the display shows the maximum peak for a sample. Various factors determine the retention time for different compounds. They include; Amount of pressure used. As the pressure increases, the flow rate of the compound increases and therefore the retention time reduces. The nature of the stationary phase also determines the retention time. The particle size is the most important factor of this nature. The components of the solvent The column’s temperature If retention time is going to be used as the parameter for identification of different components, then these factors have to be taken into account. Detector Various techniques can be used to detect presence of toluene using this method. However, ultra-violet absorption is a commonly used technique. Organic compounds absorb UV light of different wavelengths. If a beam of this kind of light is shone through a liquid flowing out of the column, a UV detector on the opposite side can be used to measure the amount of light absorbed. The volume of the compound passing through at that time also determines the amount of UV light absorbed. When there is toluene present in the component, there is a change in normal color that should be shown by the UV detector. The output of the detector is a series of peaks. Each peak represents a compound in the mixture that passes through the detector and absorbs UV light. The retention time of different compounds can be used to make conclusions of the different compounds present in the mixture. The peaks can be used as indicators of the quantities of different compounds present. The area under a peak is directly proportional to the amount of a particular compound. Fourier transformation infrared spectroscopy (FTIR) About FTIR This technique involves passing radiation through a sample, which absorbs some of it while the rest is transmitted through it. The result is a spectrum that represents the molecular absorption and transmission and a unique pattern for the sample. All molecular structures have a unique spectrum that identifies them (Jef Poortmans 789). The spectrometers collect all wavelengths simultaneously. Below is a diagram of the basic structure of the spectrometer FTIR can be useful for various kinds of analysis. It identifies various materials such as toluene that are hard to be identified using the normal ways. It also determines quality and consistency of a sample, and the magnitude of the composition of a mixture. It has several advantages including; It does not destroy the sample It does not require external calibration since it is precise It is a fast method of collecting scans It is highly sensitive Its optical throughput is higher It has only one moving part eliminating mechanical complexity The main reason behind the development of this technique was to enable the measurement of infrared frequencies simultaneously the test of toluene since it cannot be able to escape both frequencies. The simultaneous frequencies are especially vital to an optical device called an interferometer was invented for this purpose. It encodes all the infrared frequencies unto a single beam. The sample beam can be taken in a matter of seconds. Most of the interferometers in use are equipped with a device called a beamspliter. It divides the infrared signal into two beams of light. Of the beams, one is bounced off a flat mirror at a fixed point. The other beam is bounced off a mirror that moves over short distances on a mechanism built for that. The two beams come back to the splitter where they recombine. The new signal is called an interferogram. As the optical path difference between the two beams increases, the readings of different wavelengths peak (Michael Gaft 871). This gives the interferogram an oscillatory appearance. As the distance between the mirror and the splitter changes, various radiations will be in and out of phase. The frequencies of these radiations depend on frequency of movement of the mirror and that of the source (Michael Gaft 871). The interferogram contains information about every signal coming from the source. Therefore, when taking measurements of the interferogram, one takes measurement of all the infrared signals combined. A frequency spectrum is needed for success of this task. This is the plot of individual intensity at each of the points. The measured interferogram has to be decoded to take measurements of all individual frequencies. It is usually a computerized process. How to use FTI to detect toluene. The procedure adopted is for GENESIS 2 FTIR Start up the FTIR machine. Establish a directory on the computer desktop Load the software Run a background scan for the sample to be tested for toluene. Save the spectrum to your folder. Run a scan on the sample prepared. Label the peaks using the MATH > BASELINE option on the screen. The peaks will help identify the composition and quantity of the sample, including toluene if present. Print out the spectra. Shut down the procedure. Process of sample analysis of toluene Source An emitter is used to emit the infrared energy. An aperture is used to control the amount of energy that hits the sample. When toluene is present, the energy is able to detect its presence. Interferometer The beam is reflected off the two mirrors where the infrared frequencies are combined into an interferogram. The interferogram is vital to the detection of toluene. Sample This requires a professional to be able to know the different changes that toluene causes in the change of color of the infrared lights. In the sample compartment, the beam is transmitted through or is reflected off the surface. The action taken depends on the analysis being carried out. The specific frequencies unique to the sample are absorbed. Detector The devices are built specifically for one kind of spectrogram. The part is vital to the identification of the toluene. The detector is also able to detect the quantity of toluene in the sample. The computer The measurements are digitized and a computer performs Fourier transformation on them. The final output is presented to the user for his/her interpretation. For purposes of control, a background spectrum should be taken without any sample. It can then be used for comparison with the measurement of the spectrum with a sample. This comparison allows computation of the percent transmittance. This way, instrumental characteristics can be removed ensuring that all the features present are due to the sample. The instruments used for FTIR do not require having slits for resolution (White 761). This gives them a higher resolution that would be achieved using other techniques such as a dispersive instrument. A spectrometer possesses a characteristic called spectral resolution. This is its ability to distinguish between closely related features in a spectrum. The optical path difference in FTIR is the main determinant of spectral resolution. The instruments also have a short wavelength limit. The advantages outlined are responsible for giving the measurements of FTIR spectrometers highly accurate and reproducible. The technique can be relied upon for positive identification of any sample compounds (Griffiths and de Hasseth 995). With the high sensitivity, any contaminants in a sample can be easily identified. These characteristics make the techniques ideal for quality control functions in a production system or a plant. It has also been widely used in quantitative analysis tasks in many situations. This technique has gained a lot of popularity and many studies are being done on its improvement. In experimental laboratories, scientists are coming up with new ways of coming up with more precise analysis of components. In the field, it is being used for qualitative and quantitative analysis for various industries. The quality control department of any plant plays an important role in its development and performance. Work cited Griffiths, P. and J.A. de Hasseth. Fourier Transform Infrared Spectrometry. Wiley-Blackwell, 2007. Harris, Daniel C. Quantitative chemical analysis. W. H. Freeman and Company, 1999. Higson, S. Analytical Chemistry. OXFORD University Press, 2004. J.J. Kirkland, L. R. Snyder, and J. L. Glajch. Practical HPLC Method Development. New York: John Wiley & Sons, 1997. Jef Poortmans, Vladimir Arkhipov. Thin film solar cells: fabrication, characterization and applications. John Wiley and Sons, 2006. L. R. Snyder, J.J. Kirkland, and J. W. Dolan. Introduction to Modern Liquid Chromatography. New York: John Wiley & Sons, 2009. Michael Gaft, Renata Reisfeld, Gérard Panczer. Luminescence spectroscopy of vminerals and materials. Springer, 2005. Neue, U. D. Theory, Technology, and Practice. New York: Wiley-VCH, 1997. Pavia, Donald L., Gary M. Lampman, George S. Kritz, Randall G. Engel. Introduction to Organic Laboratory Techniques. Thomson Brooks/Cole, 2006. White, Robert. Chromatography/Fourier transform infrared spectroscopy and its applications. Marcel Dekker., 1990. Read More