Gas Chromatography - What It Is and How It Works

Gas Chromatography - What It Is and How It Works Gas chromatography (GC) is an analytical technique used to separate and analyze samples that can be vaporized without thermal decomposition. Sometimes gas chromatography is known as gas-liquid partition chromatography (GLPC) or vapor-phase chromatography (VPC). Technically, GPLC is the most correct term, since the separation of components in this type of chromatography relies on differences in behavior between a flowing mobile gas phase and a stationary liquid phase. The instrument that performs gas chromatography is called a gas chromatograph. The resulting graph that shows the data is called a gas chromatogram. Uses of Gas Chromatography GC is used as one test to help identify components of a liquid mixture and determine their relative concentration. It may also be used to separate and purify components of a mixture. Additionally, gas chromatography can be used to determine vapor pressure, heat of solution, and activity coefficients. Industries often use it to monitor processes to test for contamination or ensure a process is going as planned. Chromatography can test blood alcohol, drug purity, food purity, and essential oil quality. GC may be used on either organic or inorganic analytes, but the sample must be volatile. Ideally, the components of a sample should have different boiling points. How Gas Chromatography Works First, a liquid sample is prepared. The sample is mixed with a solvent and is injected into the gas chromatograph. Typically the sample size is small in the microliters range. Although the sample starts out as a liquid, it is vaporized into the gas phase. An inert carrier gas is also flowing through the chromatograph. This gas shouldnt react with any components of the mixture. Common carrier gases include argon, helium, and sometimes hydrogen. The sample and carrier gas are heated and enter a long tube, which is typically coiled to keep the size of the chromatograph manageable. The tube may be open (called tubular or capillary) or filled with a divided inert support material (a packed column). The tube is long to allow for a better separation of components. At the end of the tube is the detector, which records the amount of sample hitting it. In some cases, the sample may be recovered at the end of the column, too. The signals from the detector are used to produce a graph, the chrom atogram, which shows the amount of sample reaching the detector on the y-axis and generally how quickly it reached the detector on the x-axis (depending on what exactly the detector detects). The chromatogram shows a series of peaks. The size of the peaks is directly proportional to the amount of each component, although it cant be used to quantify the number of molecules in a sample. Usually, the first peak is from the inert carrier gas and the next peak is the solvent used to make the sample. Subsequent peaks represent compounds in a mixture. In order to identify the peaks on a gas chromatogram, the graph needs to be compared a chromatogram from a standard (known) mixture, to see where the peaks occur. At this point, you may be wondering why the components of the mixture separate while they are pushed along the tube. The inside of the tube is coated with a thin layer of liquid (the stationary phase). Gas or vapor in the interior of the tube (the vapor phase) moves along more quickly than molecules that interact with the liquid phase. Compounds that interact better with the gas phase tend to have lower boiling points (are volatile) and low molecular weights, while compounds that prefer the stationary phase tend to have higher boiling points or are heavier. Other factors that affect the rate at which a compound progresses down the column (called the elution time) include polarity and the temperature of the column. Because temperature is so important, it is usually controlled within tenths of a degree and is selected based on the boiling point of the mixture. Detectors Used for Gas Chromatography There are many different types of detectors that can be used to produce a chromatogram. In general, they may be categorized as non-selective, which means they respond to all compounds except the carrier gas, selective, which respond to a range of compounds with common properties, and specific, which respond only to a certain compound. Different detectors use particular support gases and have different degrees of sensitivity. Some common types of detectors include: Detector Support Gas Selectivity Detection Level Flame ionization (FID) hydrogen and air most organics 100 pg Thermal conductivity (TCD) reference universal 1 ng Electron capture (ECD) make up nitriles, nitrites, halides, organometallics, peroxides, anhydrides 50 fg Photo-ionization (PID) make up aromatics, aliphatics, esters, aldehydes, ketones, amines, heterocyclics, some organometallics 2 pg When the support gas is called make up gas, it means gas is used to minimize band broadening. For FID, for example, nitrogen gas (N2) is often used. The users manual that accompanies a gas chromatograph outlines the gases that can be used in it and other details. Sources Pavia, Donald L., Gary M. Lampman, George S. Kritz, Randall G. Engel (2006).  Introduction to Organic Laboratory Techniques (4th Ed.). Thomson Brooks/Cole. pp.  797–817.Grob, Robert L.; Barry, Eugene F. (2004).  Modern Practice of Gas Chromatography (4th Ed.). John Wiley Sons.Harris, Daniel C. (1999). 24. Gas Chromatography. Quantitative chemical analysis  (Fifth ed.). W. H. Freeman and Company. pp. 675–712. ISBN 0-7167-2881-8.Higson, S. (2004). Analytical Chemistry. Oxford University Press ISBN 978-0-19-850289-0

Biography of Bernardo OHiggins, Liberator of Chile

Biography of Bernardo O'Higgins, Liberator of Chile Bernardo OHiggins (August 20, 1778–October 24, 1842) was a Chilean landowner, general, president, and one of the leaders of its struggle for independence. Although he had no formal military training, OHiggins took charge of the ragged rebel army and fought the Spanish from 1810 to 1818, when Chile achieved its independence. Today, he is revered as the liberator of Chile and the father of the nation. Fast Facts: Bernardo O'Higgins Known For:  Leader during Chiles struggle for independence, general, presidentBorn:  August 20, 1778 in Chilln, ChileParents: Ambrosio OHiggins and Isabel RiquelmeDied:  October 24, 1842 in Lima, PeruEducation: San Carlos College, Peru, Catholic school in EnglandNotable Quote: Lads! Live with honor, or die with glory! He who is brave, follow me! Early Life Bernardo was the illegitimate child of Ambrosio OHiggins, a Spanish officer born in Ireland who immigrated to South America and rose through the ranks of the Spanish bureaucracy, eventually reaching the high post of Viceroy of Peru. His mother Isabel Riquelme was the daughter of a prominent local, and he was raised with her family. Bernardo only met his father once (and at that time he did not know who he was) and spent most of his early life with his mother and traveling. As a young man, he went to England, where he lived on a small allowance that his father sent him. While there, Bernardo was tutored by legendary Venezuelan Revolutionary Francisco de Miranda. Return to Chile Ambrosio formally recognized his son in 1801 on his deathbed, and Bernardo suddenly found himself the owner of a prosperous estate in Chile. He returned to Chile and took possession of his inheritance, and for a few years he lived quietly in obscurity. He was appointed to the governing body as the representative of his region. Bernardo might well have lived his life as a farmer and local politician if it were not for the great tide of independence that was building in South America. OHiggins and Independence OHiggins was an important supporter of the September 18 movement in Chile, which began the nations struggle for independence. When it became apparent that the actions of Chile would lead to war, he raised two cavalry regiments and an infantry militia, mostly recruited from families who worked his lands. As he had no training, he learned how to use weapons from veteran soldiers. Juan Martà ­nez de Rozas was president and OHiggins supported him, but Rozas was accused of corruption and criticized for sending valuable troops and resources to Argentina to help the independence movement there. In July 1811, Rozas stepped down and was replaced by a moderate junta. OHiggins and Carrera The junta was soon overthrown by Josà © Miguel Carrera, a charismatic young Chilean aristocrat who had distinguished himself in the Spanish army in Europe before deciding to join the rebel cause. OHiggins and Carrera would have a tempestuous, complicated relationship for the duration of the struggle. Carrera was more dashing, outspoken, and charismatic, while OHiggins was more circumspect, brave, and pragmatic. During the early years of the struggle, OHiggins was generally subordinate to Carrera  and dutifully followed his orders as best he could. This power dynamic would not last, however. The Siege of Chilln After a series of skirmishes and small battles against the Spanish and royalist forces from 1811–1813, OHiggins, Carrera, and other rebel generals chased the royalist army into the city of Chilln. They laid siege to the city in July of 1813, in the middle of the harsh Chilean winter. The siege was a disaster for the rebels. The patriots could not completely dislodge the royalists. When they did manage to take part of the town, the rebel forces engaged in raping and looting, which caused the province to sympathize with the royalist side. Many of Carreras soldiers, suffering in the cold without food, deserted. Carrera was forced to lift the siege on August 10, admitting that he could not take the city. Meanwhile, OHiggins had distinguished himself as a cavalry commander. Appointed Commander Not long after Chilln, Carrera, OHiggins, and their men were ambushed at a site called El Roble. Carrera fled the battlefield, but OHiggins remained despite a bullet wound in his leg. OHiggins turned the tide of the battle and emerged a national hero. The ruling junta in Santiago had seen enough of Carrera after his fiasco at Chilln and his cowardice at El Roble and made OHiggins commander of the army. OHiggins, always modest, argued against the move, saying that a change of high command was a bad idea, but the junta had decided: OHiggins would lead the army. The Battle of Rancagua OHiggins and his generals battled Spanish and royalist forces throughout Chile for another year before the next decisive engagement. In September 1814, Spanish General Mariano Osorio was moving a large force of royalists into position to take Santiago and end the rebellion. The rebels decided to make a stand outside the town of Rancagua, on the way to the capital. The Spanish crossed the river and drove off a rebel force under Luà ­s Carrera (brother of Josà © Miguel). Another Carrera brother, Juan Josà ©, was trapped in the city. OHiggins bravely moved his men into the city to reinforce Juan Josà © in spite of the approaching army, which far outnumbered the rebels in the city. Although OHiggins and the rebels fought very bravely, the result was predictable. The massive royalist force eventually  drove the rebels out of the city. The defeat could have been avoided had Luà ­s Carreras army returned, but it did not- under orders from Josà © Miguel. The devastating loss at Rancagua meant that Santiago would have to be abandoned: There was no way to keep the Spanish army out of the Chilean capital. Exile OHiggins and thousands of other Chilean rebels made the weary trek into Argentina and exile. He was joined by the Carrera brothers, who immediately began jockeying for position in the exile camp. Argentinas independence leader,  Josà © de San Martà ­n, supported OHiggins, and the Carrera brothers were arrested. San Martà ­n began working with Chilean patriots to organize the liberation of Chile. Meanwhile, the victorious Spanish in Chile were punishing the civilian population for their support of the rebellion. Their harsh brutality only caused the people of Chile to long for independence. When OHiggins returned, the general population was ready. Return to Chile San Martà ­n believed that all of the lands to the south would be vulnerable as long as Peru remained a royalist stronghold. Therefore, he raised an army. His plan was to cross the Andes, liberate Chile, and then march on Peru. OHiggins was his choice as the man to lead Chiles liberation. No other Chilean commanded the respect that OHiggins did (with the possible exception of the Carrera brothers, whom San Martà ­n did not trust). On January 12, 1817, a formidable rebel army of some 5,000 soldiers set out from Mendoza to cross the mighty Andes. Like  Simà ³n Bolà ­vars epic 1819 crossing of the Andes, this expedition was very harsh. San Martà ­n and OHiggins lost some men in the crossing, although their sound planning meant that most soldiers survived. A clever ruse had sent the Spanish scrambling to defend the wrong passes and the army arrived in Chile unopposed. The Army of the Andes, as it was called, defeated the royalists at the  Battle of Chacabuco  on February 12, 1817, clearing the path to Santiago. When San Martà ­n defeated the Spanish last-gasp attack at the  Battle of Maipu  on April 5, 1818, the rebel victory was complete. By September 1818, most Spanish and royalist forces had retreated to try to defend Peru, the last Spanish stronghold on the continent. End of the Carreras San Martà ­n turned his attention to Peru, leaving OHiggins in charge of Chile as a virtual dictator. At first, he had no serious opposition: Juan Josà © and Luis Carrera had been captured attempting to infiltrate the rebel army. They were executed in Mendoza. Josà © Miguel, OHiggins greatest enemy, spent the years from 1817 to 1821 in southern Argentina with a small army, raiding towns in the name of gathering funds and weapons for liberation. He was finally executed after being captured, ending the long-standing and bitter OHiggins-Carrera feud. OHiggins the Dictator OHiggins, left in power by San Martà ­n, proved to be an authoritarian ruler. He hand-picked a Senate and the 1822 Constitution allowed representatives to be elected to a toothless legislative body.  OHiggins was a de facto dictator. He believed that Chile needed a strong leader to implement change and control simmering royalist sentiment. OHiggins was a liberal who promoted education and equality and curtailed the privileges of the wealthy. He abolished all noble titles, even though there were few in Chile. He changed the tax code and did much to encourage commerce, including the completion of the Maipo Canal. Leading citizens who had repeatedly supported the royalist cause saw their lands taken away if they had left Chile and they were heavily taxed if they remained. The Bishop of Santiago, the royalist-leaning Santiago Rodrà ­guez Zorrilla, was exiled to Mendoza. OHiggins further alienated the church by allowing Protestantism into the new nation and by reserving the right to meddle in church appointments. He made many improvements to the military, establishing different branches of service, including a Navy to be led by the Scotsman Lord Thomas Cochrane. Under OHiggins, Chile remained active in the liberation of South America, often sending reinforcements and supplies to San Martà ­n and  Simon Bolà ­var, then fighting in Peru. Downfall OHiggins support began to erode quickly. He had angered the elite by taking away their noble titles and, in some cases, their lands. He then alienated the commercial class by continuing to contribute to expensive wars in Peru. His finance minister Josà © Antonio Rodrà ­guez Aldea was revealed to be corrupt, using the office for personal gain. By 1822, hostility to OHiggins had reached a crucial point. The opposition to OHiggins gravitated towards General Ramà ³n  Freile as a leader, himself a hero of the Independence wars, if not a hero of OHiggins stature. OHiggins attempted to placate his foes with a new constitution, but it was too little, too late. Seeing that cities were prepared to rise against him in arms, OHiggins agreed to step down on January 28, 1823. He remembered only too well the costly feuding between himself and the Carreras and how a lack of unity had almost cost Chile its independence. He went out in dramatic fashion, baring his chest to the assembled politicians and leaders who had turned against him and inviting them to take their bloody revenge. Instead, all present cheered for him and escorted him to his home. Exile General Josà © Marà ­a de la Cruz claimed that OHiggins peaceful departure from power avoided a good deal of bloodshed and said, OHiggins was greater in those hours than he had been in the most glorious days of his life. Intending to go into exile in Ireland, OHiggins made a stop in Peru, where he was warmly welcomed and given a large estate. OHiggins had always been a somewhat simple man and a reluctant general, hero, and president, and he happily settled into his life as a landowner. He met Bolà ­var and offered his services, but when he was offered only a ceremonial position, he returned home. Final Years and Death During his final years, OHiggins acted as an unofficial ambassador from Chile to Peru, although he never did return to Chile. He meddled in the politics of both countries, and he was on the verge of being unwelcome in Peru when he was invited back to Chile in 1842. He did not make it home, as he died of heart trouble while en route on October 24, 1842. Legacy Bernardo OHiggins was an unlikely hero. He was a bastard for most of his early life, unrecognized by his father, who was a devout supporter of the king. Bernardo was ingenious and dignified, not particularly ambitious nor an especially dazzling general or strategist. He was in many ways as unlike Simà ³n Bolivar as it is possible to be: Bolà ­var had much more in common with the dashing, confident Josà © Miguel Carrera. Nevertheless, OHiggins had many positive qualities that were not always apparent. He was brave, honest, forgiving, and dedicated to the cause of liberty. He did not back down from fights, even those he could not win. During the wars of liberation, he was often open to compromise when more stubborn leaders like Carrera were not. This prevented unnecessary bloodshed among rebel forces, even if it did mean repeatedly allowing the hot-headed Carrera back into power. Like many heroes, most of OHiggins failings have been forgotten and his successes are exaggerated and celebrated in Chile. He is revered as the Liberator of his country. His remains lie in a monument called The Altar of the Fatherland. A city is named after him, as well as several Chilean navy ships, countless streets, and a military base. Even his time as dictator of Chile, for which he has been criticized for clinging too tightly to power, is viewed by many historians as more beneficial than not. He was a strong personality when his nation needed guidance, yet by most accounts, he did not overly repress the people or use his power for personal gain. Many of his liberal policies, seen as radical at the time, are respected today. Sources Concha Cruz, Alejandor and Maltà ©s Cortà ©s, Julio.  Historia de Chile.  Bibliogrfica Internacional, 2008.Harvey, Robert.  Liberators: Latin Americas Struggle for Independence. The Overlook Press, 2000.Lynch, John.  The Spanish American Revolutions 1808–1826. W. W. Norton Company, 1986.Scheina, Robert L.  Latin Americas Wars, Volume 1: The Age of the Caudillo 1791–1899. Brasseys Inc., 2003.Concha Cruz, Alejandor and Maltà ©s Cortà ©s, Julio.  Historia de Chile  Santiago: Bibliogrfica Internacional, 2008.Harvey, Robert.  Liberators: Latin Americas Struggle for Independence.The Overlook Press, 2000.Lynch, John.  The Spanish American Revolutions 1808-1826. W. W. Norton Company, 1986.Scheina, Robert L.  Latin Americas Wars, Volume 1: The Age of the Caudillo 1791-1899. Brasseys Inc., 2003.