Samples

16 February, 2022

34 minutes read

Author:  Elizabeth Brown

Chemistry Essay for everyone – topics, samples and guade how to write

If you’re a science department student, you will likely have no questions about what a Chemistry essay is. You’re probably well-versed with a variety of academic papers on this subject. But even if you’re new to this field, here we familiarize students with the basics of Chemistry writing and explain the fundamentals of planning and […]

chemistry essay

If you’re a science department student, you will likely have no questions about what a Chemistry essay is. You’re probably well-versed with a variety of academic papers on this subject. But even if you’re new to this field, here we familiarize students with the basics of Chemistry writing and explain the fundamentals of planning and […]

If you’re a science department student, you will likely have no questions about what a Chemistry essay is. You’re probably well-versed with a variety of academic papers on this subject. But even if you’re new to this field, here we familiarize students with the basics of Chemistry writing and explain the fundamentals of planning and completing an essay. Stay tuned, and you will learn all ins and outs of professional, competent essay composition.

First, let’s clarify what this assignment means. When you receive a task to write on some Chemistry-related topic, it’s most often a task meant to check your comprehension of a scientific principle, topic, or area. So, you’re expected to conduct thorough research, check what other people say on that issue, what positions they argue, and which of those positions or assumptions is closer to you. Once you pick a standpoint, you can write your own academic piece arguing that point and supporting your views with reliable evidence.

If you’ve received such a task and don’t know how to approach it, you may turn to our experts’ help with this subject. You’re guaranteed an individual approach to any assignment entrusted to our experts and top-notch content produced on any Chemistry theme.

Chemistry Essay Format

Completing Chemistry homework is a bit different from writing a Human Resources management essay or a Human Resources school essay. Here, you cannot experiment that much with arguments and theories; you need to stick to the objective facts, formulas, and evidence from your textbook. The Chemistry format typically includes the following parts.

Introduction

This element of your Chemistry paper should introduce the topic to the readers and communicate what you’re planning to examine. Once you provide those details to your audience, you can rest assured that even laypersons will capture the significance of your subject. Besides, you clarify your stand on the issue, thus helping your readers evaluate the strength and persuasiveness of your arguments. 

Body

The body of your paper typically takes 80-90% of the entire paper’s volume, so you need to include several meaningful paragraphs into it. Dedicate one paragraph to every idea you’re using to argue your stand, and your readers will follow the line of argumentation much easier this way.

Conclusion

This is the last part of your essay, but don’t underestimate its significance for your assignment’s value and correctness. Here, you need to show what you’ve achieved and learned in the process of academic inquiry, thus showing your progress and restating the study’s significance.

Write Chemistry Essay in 5 Steps

Now let’s proceed to the mechanics of writing a paper on Chemistry. It’s pretty simple to compose a great work if you have a tried and tested algorithm at hand and can complete a good-looking, professional paper.

  1. Find examples of similar assignments to use their structure and approach. Obviously, you can take a look at some Human Resources school essay examples available online, but keep in mind that a Chemistry report is not a typical Human Resources plan essay. It should be focused on a specific topic, such as, for instance, organic chemistry, acid reactions, etc., and follow a predetermined format.
  2. Pick a topic that you know well. It’s easier to compose a paper on Chemistry if you know what you’re talking about and are genuinely interested in learning the subject in more depth.
  3. Follow the prompt that your Chemistry professor gave to you. It’s even better if you have a Chemistry example and can reproduce it step by step (though without copy-pasting).
  4. Draft the paper and include all evidence you’ve found in the research process. Distribute the evidence and arguments evenly by dedicating one paragraph to every single idea. In this way, the paper will be coherent and readable.
  5. Reread your draft to identify typos or flow inconsistencies. By correcting these minor issues, you polish the paper to perfection and prepare it for the final submission.

As you can see, completing such an assignment is not hard at all. Follow these tips and steps to finalize the essay quickly, and you will save lots of time for other priorities and tasks.

Chemistry Topics

Are you unsure about the Chemistry topics to examine? Here is a list of evergreen suggestions that are sure to incite the interest of your readers and win you a high grade.

  1. The chemical fundamentals of healthy, correct nutrition.
  2. The exciting chemistry of fireworks.
  3. The innovative scientific field of computational chemistry.
  4. Synthesis and transformation of organic substances.
  5. Chemical synthesis of oligonucleotides.
  6. The fundamentals of heterocyclic chemistry.
  7. Stellar evolution and the spectral classes of stars.
  8. How can one predict new chemical elements and compounds?
  9. Atomic and physical properties of hydrogen. 
  10. Are atomic weights precisely known or still uncertain?
  11. Protonic acids and bases.
  12. Introduction to the hydrogen bond. 
  13. Discovery and isolation of chemical elements.
  14. The ionic-bond model.
  15. Availability and distribution of chemical elements on the Earth.
  16. Availability of rare chemical elements in space.
  17. The introduction to hydroxides.
  18. The chemical properties of alkali metals.
  19. Introduction to the property of chemical reactivity.
  20. Oxoacid salts: properties and practical use.
  21. Isolation and purification of boron.
  22. Bonding and topology of aluminum compounds.
  23. Allotropic forms of carbon.
  24. Practical application of graphite intercalation compounds.
  25. Atomic and physical properties of silicon.
  26. Production and uses of germanium.
  27. Nitrous acid and nitrites.
  28. The industrial use of phosphorus-nitrogen compounds.
  29. Chemical reactivity and group trends of arsenic.
  30. Physiological activity of arsenicals.
  31. Chemical properties of O2.
  32. Aqua complexes and solid hydrates: water types.
  33. Different methods for classifying oxides.

All of these are argumentative Chemistry topics, which means that you will have enough space and freedom to pick a position and argue it with the help of reliable evidence. Choose any of the recommended themes, and you are guaranteed an excellent grade.

How to Start a Chemistry Essay

Starting a Chemistry paper may turn into a challenge for those new to such types of assignments. But don’t fall into despair. Here are some pro tips to simplify the process:

  • Study the prompt carefully to see what the professor wants to see in the assignment’s text.

Many students make the mistake of hasting to write something as soon as possible. As a result, they end up with off-topic assignments that they cannot submit to the professor. Don’t commit that error; always study the instructions and proceed to research and writing only after you’re 100% sure about the expected essay outcome.

  • Focus on the topic that you already know.

Don’t start something anew if you’re short of time and want to complete an essay quickly. It’s always easier to expand your knowledge on the topic you already know well, thus writing a good-looking essay hassle-free.

  • Use only argumentative topics if you’re given the freedom of choice.

It’s much simpler to compose something interesting and thought-provoking on an argumentative subject than just review what people know about a specific chemical substance or reaction. Today, chemistry is a trendy science, so you may find numerous exciting ideas and suggestions for its practical value for humanity.

We have a large writer team specializing in all kinds of essay writing, Human Resources to Chemistry to Programming to Literature. Thus, you will always have a realm of talented authors at your service, available 24/7 to deliver top-notch papers on demand.

You can always find a capable Chemistry writer in our company, thus entrusting your assignment to professionals and not worrying about the outcomes.

#1

Determination of Potassium and the reactions of Li, Na and K

Introduction and theory

Chemists are frequently charged with the responsibility of performing assays on different compounds. An assay is defined by two parameters: quality and quantity of a certain substance. In this case, we are provided with KB(Ph)4 to analyze. In the first part, we are to determine the quantity of potassium (K) in his compound and in the second part we are to test various group 1 salts to see their specific reactions.
During gravimetric determination of potassium, sodium tetraphenylboron acts as a precipitator for the potassium ions. A definite volume of sodium ions is added to the sample solution and used in determining the concentration.
Alkali metals react with many chemical substances and hence have many physical and chemical properties. Their properties differ with the individual elements. For example, lithium burns with a red flame, sodium with a yellow-orange one while potassium burns with a purple one. Their reactivity increases from lithium to potassium and this greatly defines the difference in their reaction patterns.

Method 1

Part 1

25cm3 of the K solution was pipetted in a 250cm3 beaker and a few drops of dilute NaOH and bromothymol blue indicator added to it. Any precipate formed at that point was then filtered off. 5% ethanoic acid was added until the colour of the solution changed to yellow. The solution was then diluted to 100 cm3 with H2O and heated to 65ºC. 15 cm3 of 2% sodium tetraphenylboron solution was then added to the heated solution while stirring.
The solution was then cooled to room temperature; it took 10 minutes to do so. The solution was then filtered through a pre-weighed No. 4 sintered glass crucible into a clean Buchner flask. The filtrate was then tested for complete precipitation with a few drops of the reagent. On further precipitation, the filtrate was transferred into a beaker, a further 10cm3 added and the solution re-filtered. The precipitate was washed with 5% ethanoic acid and dried between 110 ºC to 120 ºC for 30 minutes. The precipitate was then cooled and weighed as KB(Ph)4 and used to get the concentration f the original solution.

Part 2

Dilute solutions of Li+, Na+ and K+ were treated as follows:
1. By flame test
2. Addition of excess ammonical ammonium fluoride
3. Addition of dilute ethanoic acid followed by sodium cobaltinitrate (aq)
4. Addition, dropwise and carefully of potassium perchlorate
The above processes were carried out in a test tube and observations recorded.
Method 2
A mixture of LiCl and KCl (about 0.3g) was shaken with 6 cm3 of absolute ethanol in a closed tube. The residual solid was separated by filtration and the residue washed with 3 1cm3 portions of ethanol. The filtrate and the washings were then combined and evaporated to dryness. The resultant solid was then dissolved in 2cm3 of H2O.
Icm3 portions were tested for lithium
a) With ammonium fluoride 1cm3 4 mol dm-3 and conc. Ammonia (dropwise).
b) Potassium with a solution of sodium cobaltinitrate 1cm3, 0.2 mol dm-3)
The original residual solid was separated by filtration and dissolved in 2cm3 H2O and portions tested for lithium and potassium in the same manner.

Results

Method 1

Part 1

Weight for empty sample = 39.419g
Weight of dry sample =39.930g
Difference in weight (Amount of potassium) = 0.511g

Part 2

test
Li
Na
K
1
Red flame
Orange flame
Purple flame
2
No observable change
No observable change
No observable change
3
No observable change
No observable change
No observable change
4
No observable change
No observable change
No observable change

Discussion

In the first part of formation of KB(Ph)4 the reaction is as described by this equation:
K+ + NaB(Ph)4 = KB(Ph)4 + Na+
The colour change to yellow is due to excess acid after the achieved end point.
For the flame test, all alkali metals burn in presence of oxygen to form oxides and sometimes form peroxides in excess oxygen. They burn with different characteristic colours.
4Li + O2 = 2Li2O Red flame
4Na + O2 = 2Na2O Yellow-orange flame
4K + O2 = 2K2O Purple flame
For the ammonical ammonium fluoride, alkali metals displace ammonium ions from their anions to form soluble salts. The reactions are as follows:
Li+ + NH4F = LiF + NH4+
K+ + NH4F = KF + NH4+
Na+ + NH4F = NaF + NH4+
Ethanoic acid then sodium cobaltinitrate, displacement reactions occur between the alkali metal ions to form soluble products. The reactions are as follows:
CH3COOH + Li = CH3COOLi
CH3COOLi+ Na3Co(NO2)6 = CH3COONa + Li3Co(NO2)6
CH3COOH + Na = CH3COONa
CH3COONa + Na3Co(NO2)6 = no reaction
CH3COOH + K = CH3COOK
CH3COOK+ Na3Co(NO2)6 = CH3COONa + K3Co(NO2)6
With potassium perchlorate, displacement reactions occur between the alkali metal ions to form soluble products. The reactions are as follows:
CH3COOLi + KClO4 =CH3COOK + Li CLO4
CH3COONa+ KClO4 =CH3COOK + NaCLO4

Conclusion

Lithium, sodium and potassium burn with red, orange and purple flames respectively. Most of the group 1 elements form soluble salts.

References

Belcher, R. & Wilson, C. L. New methods in analytical chemistry. Chapman and Hall, 1955.
Chemical Society, Chemical Society (Great Britain). Inorganic chemistry of the main-group elements. Chemical Society, 1971.

#2

NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY (NMR)

(Author’s name)
(Institutional Affiliation)

Abstract

Nuclear Magnetic Resonance (NMR) is becoming a powerful techniques used to determine the molecular structure of organic and inorganic compounds. Its acceptability is mainly due to the several advantages is has such as reproducibility, accuracy and the ability to have mathematical equations (Maniara et al. 1998). A study done to determine the purity of glyphosate using an Uncertainty Budget, by Quantitative Nuclear Magnetic Resonance Spectroscopy (QNMR) confirms these qualities of NMR. The finding from the study was that, a big part in the uncertainties of the methods used, that is 1H and 31P, was the standard deviation of the replicate. The study concluded that an alternative organic phosphate, with similar nOe, may therefore be preferred as a calibrator (Tareq et al. 2004).

Key words

NMR, technique, molecular structure, glyphosphate

Introduction

The discovery of nuclear magnetic resonance spectroscopy (NMR), as a qualitative technique, has made possible the identification and elucidation of chemical structures in organic and inorganic compounds. According to Maniara et al (1998), quantitative NMR (QNMR) has gained acceptance since it is accurate, precise, no calibrator is needed for the analyte. It can also be described by mathematical equations which can be used at the highest metrological level (Janke, 1998).
Advantages of NMR
Janke (1998) concluded that NMR is a cost effective analytical method since it not only shows all present soluble substances but also identifies impurities with similar structures. It is a non destructive technique with minimal sample preparations for analytes that contain 19F, 13C, 1H and 31P (Lee et al., 2001). Marina (1998) was able to show that QNMR was reproducible using 1H and 31P. Henderson (1996), using several agricultural weedicide, was able to show that by using coaxial inserts, it would be possible to eliminate sources of error in conventional quantification NMR spectroscopy.

Research on NMR

A study done to determine the purity of glyphosate using an Uncertainty Budget, by Quantitative Nuclear Magnetic Resonance Spectroscopy (QNMR) using 1H and 31P, is an example of the reproducibility of a type A uncertainty combined by other type B effects. Reagents used included Analytes such as glyphosate, certified reference material e.g dimethylsulfone, deuterated NMR Solvents like deuterium oxide D. The results supported all the qualities that are mentioned above about QNMR (Tareq et al. 2004).
Another finding from the study was that, a big part in the uncertainties of the methods used, that is 1H and 31P, was the standard deviation of the replicate. A bottom up analysis was attempted to estimate the effects that contributed to this term was able to identify half of the standard deviation measured. Effects from the operator while weighing had the greatest effects. About 0.23% of the remaining uncertainty was assigned to heterogeneity of the contaminations in the sub samples. Since impurities in the solid samples do not distribute homogeneously, no effort was made to grind and mix the samples prior to the analysis (Tareq et al. 2004).
The contributions of the uncertainty budget in the standard deviations of the results were standard deviations of the means. The calculated purity from the replicated data was related to the combined standard uncertainty from each determination. The calculation for the uncertainty was 0.82% for 31P NMR and 0.66% for 1H NMR. Despite trisodium phosphate being excellent in purity, water soluble, and chemically stable, its use as a calibrator for 31P NMR can lead to a bias with concomitant uncertainty. This is due to the absence of protons in its electron configuration and so cannot exhibit nOe. The study concluded that an alternative organic phosphate may therefore be preferred as a calibrator (Tareq et al. 2004).

Bibliography

Janke, H. 1998. CCQM/98 98: 1 – 12.
Maniara, G., Rajamoorthi, K., Rajan, S. and Stockton, G. W. (1998). Quantitative NMR Spectroscopy Anal. Chem. 70, 4921- 4928.
Tareq Saed Al-Deen, D. Brynn, Hibbert, James. M. Hook and Robert J. W. (2004). An uncertainty budget for the determination of the purity of glyphosate by quantitative nuclear magnetic resonance (QNMR) spectroscopy. Accreditation and Quality Assurance, 9, 55-63.

#3 Uncertainty Estimates

Name
Institution
Lecturer
Course
Date

Summary of the Article

The article, “Is My Uncertainty Estimate Realistic”, by Analytical Method Committee (2003), is about the realism of uncertainty estimates. The author poses and explicates the issue that uncertainty estimates often quoted by analysts in their results are somewhat low. According to the author, it is practically impossible to incorporate all the factors contributing to uncertainty estimate when determining the standard deviation from repeated results that have been obtained from repeatability conditions. There are various factors that contribute to uncertainty estimate including the difference in the way analysts interpret method protocol in different laboratories, difference in runs for the same method and numerous, systematic errors, such as calibration differences and difference in permitted variations. However, it is quite difficult to avoid such factors that contribute towards method, laboratory and run bias.
Therefore, it is paramount to check that the uncertainty estimates used or quoted are realistic to apply the effective corrective measure to unrealistic uncertainty estimates that have been found. The author gives different ways of checking for uncertainty estimates. These include, checking standard uncertainty estimate against collaborative trial statistics, comparing the indicated uncertainty with reproducibility standard deviation that has been estimated from available repeatability precision statistics and examining the proficiency test results. Once uncertainty estimates have been found, the author gives different ways through which such estimates can be corrected. An analyst can eliminate identified causative factors or apply an appropriate correction to the identified causative factor. Other strategies include basing uncertainty estimate on interlaboratory study, increase expansion factor or add an arbitrary term to the uncertainty budget.
1. What is the paper about?
The paper is about the realism of uncertainty estimate. It describes uncertainty estimates in laboratory tests, how to check if uncertainty estimates are realistic and how to correct uncertainty estimates that are unrealistic.
2. What are the issues raised?
The author indicates that, in many instances, the uncertainty estimates cited by analysts are somewhat low and, therefore, unrealistic. The author clarifies this problem by indicating that if interlaboratory studies results are observed, such as proficiency tests and collaborative trials, one will find that the uncertainty estimates used are unrealistic. The problem of unrealistic uncertainty is so because it is often impractical to avoid and confirm the absence of all errors arising from method, laboratory and run bias. There are various sources of errors that contribute to results dispersion and many analysts often do not take them into account when determining their uncertainty budgets. Accordingly, it is crucial to check if the uncertainty estimates are realistic to apply corrective measures to any unrealistic uncertainty estimate.
3. Does the paper agree with Professor Hibbert’s book?
Yes, the paper agrees with the book especially on checking and correcting unrealistic uncertainty estimate. Hibbert, in his book outlines the steps necessary to check and correct uncertainty estimates, which include:

  • Specifying the measurand;
  • Identifying the main sources of uncertainty;
  • Determining the magnitude of the various uncertainty components;
  • Combining the various significant uncertainty components that have been identified;
  • Reviewing the estimates and reporting the measurement uncertainty.

The Analytical Method Committee (2003) has given the same procedure of identifying and correcting uncertainty estimates. Particularly, the article, like in Gilbertt’s book, eliminating uncertainty estimates involves identifying and correcting the main components of uncertainty estimates.
4. How does the topic fit in the overall problem of quality in the laboratory?
The topic is extremely helpful in improving quality in laboratory tests, especially in analytical chemistry. Knowing that it is often impossible to avoid and confirm the absence of all errors arising from method, laboratory and run bias, the knowledge on how to check and correct uncertainty estimates helps in improving the quality of laboratory results. For instance, the article has suggested various methods of determining unrealistic uncertainties and correcting them. Therefore, analysts will be able to indicate realistic uncertainties in their results, which will help in improving laboratory results through increased validity and reliability.
5. Are there any other papers or published material on this topic (post a bibliography)?
There are other papers and published material on the topic as described in the bibliography.
a. A Method to Estimate the Uncertainty of Measurements in a Conglomerate of Instruments/Laboratories by Kallner, Khorovskaya and Pettersson (2005)
This is a research article in which the authors address the issues of repeatability and reproducibility of laboratory tests. The authors conclude that variations often arise regarding laboratory results, which may pose a serious threat depending on the application of the test results. Accordingly, the authors provide an applicable approach for measuring and correcting uncertainty estimates in measurements.
b. The Evaluation of Measurement Uncertainty from Method Validation Studies by Barwick, Ellison, Rafferty and Gill (2000).
This is a research paper in which the authors develop a protocol for measuring uncertainty estimates. Calculation of uncertainty estimates is crucial in deciding a corrective measure to ensure that laboratory results are valid and reliable.

Bibliography

Analytical Method Committee (AMC). 2003. AMC Technical Brief: Is my Uncertainty Estimate
Realistic? Royal Society of Chemistry.
Barwick, V.J, Ellison, L.R, Rafferty, J.Q & Gill, R.S. 2000. “The Evaluation of Measurement
Uncertainty from Method Validation Studies. Part 2: The Practical Application of a
Laboratory Protocol”. Accred Qual Assur, vol 5, pp. 104-113.
Kallner, A, Khorovskaya, L, & Pettersson, T. 2005. “A Method to Estimate the Uncertainty of
Measurements in a Conglomerate of Instruments/Laboratories”. Scandinavian Journal of
Clinical & Laboratory Investigation, Vol 65, pp. 551-558.

#4 Competence in Measurement

Name
Institution
Lecturer
Course
Date

Article 1:
What is the paper about?
The paper is about accreditation and its ability to ensure competence in measurement. The paper describes accreditation, shows the need for ensuring competence through common understanding of the measurement concepts and how to ensure common understanding of the concepts (Bievre 2008).
What are the issues raised?
The author posits that accreditation, against an ISO Standard, is a must for measurement laboratories based on the notion that accredited laboratories are competent. However, the author wonders if such accreditation results to real and demonstrated competence, which is crucial in laboratory measurement. Real and demonstrated competence would be possible if assessors were able to understand and explain the key concepts forming the basis of the assessment and accreditation. Therefore, there is a dire need for the assessors and measurement laboratories to understand the various measurement concepts for accreditation to ensure competence in measurements. Professional bodies tasked with ensuring common understanding of the measurement concepts, including IUPAC and ISO, have come up with strategies to ensure common understanding of the concepts. Such strategies include, for example, the International Vocabulary of Metrology-Basic and General Concepts and Associated Terms developed and provided by ISO.
Does the paper agree with Professor Hibbert’s book?
Yes, the paper agrees with Professor Hibbert’s book especially on the importance of a common understanding of the measurement concepts, such as the measurand, in ensuring competence in laboratory measurements. Bievre (2008) has stressed on the same issue, indicating that common understanding of the concepts will ensure consistency of answers when accrediting against international standards.
How does the topic fit in the overall problem of quality in the laboratory?
The topic contributes towards ensuring quality in the laboratory through competence resulting from accreditation. In other words, accreditation will work towards ensuring competence and eventually quality improvement in the laboratory. If analysts and assessors have a common understanding of the measurement concepts and the terminologies arising from them, accreditation will be meaningful, and it will ensure competence is measurement.
Article 2:
What is the article about?
The article is about the need for competent assessors especially in understanding what they are assessing and performing measurement uncertainty (Bievre 2011).
What are the issues raised?
Bievre (2011) begins by indicating the need for specifying measurement uncertainty during accreditation considering that measurements have uncertainties (measurement results vary with procedures). Accordingly, the author posits that assessors should not consider measurement methods to have constant measurement uncertainty because measurement uncertainty vary with various parameters, the most crucial being the level of skill, competence, professionalism and accuracy an analyst shows when carrying out measurement procedures. Therefore, an assessor should evaluate the measurement procedure when evaluating and accrediting. In doing so, assessors are able to evaluate the consistency between declared measurement uncertainty and the analyst’s skills and competence. Therefore, assessors should have a clear understanding of what analysts are measuring to assess them effectively. Consequently, assessors should be knowledgeable on establishing metrological traceability and measurement procedures to ensure competence in measurement when assessing and accrediting measurement laboratories.
Does the paper agree with Professor Hibbert’s book?
Yes, the paper agrees with the book especially on uncertainty. The article outlines the various sources of variance in measurement results including the level of competence and accuracy during measurement, which call for the need for measurement uncertainty in accreditation. Similarly, Professor Hibbert talks about measurement uncertainty, the need to measure and consider it.
How does the topic fit in the overall problem of quality in the laboratory?
The paper is particularly helpful in improving the quality in laboratory measurements by ensuring that accreditation of laboratory measurements ensure competence in measurement. Competent and knowledgeable assessors will ensure competence in laboratory measurements by assessing the skills and competence of the analysts, which will ensure quality, competence and professionalism in laboratories. In other words, accreditation will help in ensuring competence in laboratories.

Bibliography

Bievre, P. 2008. ‘Does Accreditation Ensure Competence in Measurement?’ Accred Qual Assur,
vol. 16, pp. 1-2.
Bievre, P. 2011. ‘Does Accreditation Ensure Competence in Measurement?’ Accred Qual Assur,
vol. 13, pp. 1-2.

#5

What is supercritical fluid chromatography (SFC)? Compare supercritical fluid chromatography (SFC) with other column chromatographic methods.
Supercritical fluid chromatography is a chemical separation method that uses supercritical forms of gases. The term supercritical is used for highly compressed chemical gases such that they possess both the characteristics of a gas and characteristics of a liquid .In other words, a substance is referred as a supercritical fluid when both its pressures and its temperatures are above its critical pressure and temperature. While a critical temperature is the temperature of a substance above which the liquid phase will not exist, critical pressure is the vapor pressure at the critical temperature of a substance. Density, refractive index, and viscosity are some of the properties of supercritical fluid. These however vary with temperature and pressure. SFH is similar to other column chromatographic methods like HPLC given that they utilize the similar principle. One of the variations is the fact that SFC typically utilizes CO2 as the mobile phase thus the need to pressurize the entire chromatographic flow path. In SFH just like in HPLC, separation is affected by variation of the mobile phase composition. For supercritical fluid chromatography, unlike other column chromatographic methods can be used within a wide range of sensitive detectors. IN GC and HPLC, the type of detector to be used is dominated by the mobile phase whereas SFC utilizes mobile phase, which can either be liquid like or gas like.
List some of the advantageous properties of supercritical CO2 as a mobile phase for chromatographic separations. How analytes are usually recovered after an SFC?
Often, supercritical CO2 is used in the mobile phase of supercritical fluid chromatography. CO2 remains one of the most useful in this case due to its ready availability .Other advantages of CO2 include low cost, low interference with chromatographic detectors, nontoxicity, low critical temperature ,inflammability and that it can permit aflame ionization detector to be used, with all the benefits in terms of ease of use, linearity and sensitivity.
How do instruments for supercritical fluid chromatography differ from those for (a) HPLC and (b) GC?
The major difference between the instruments used in supercritical fluid chromatography and high performance liquid chromatography is the number of analytical columns used. In the former, two types of analytical columns areused, that is, Capillary columns of fused silica coated with cross-linked chemically bonded stationary phases and packed columns that are meant for high-performance liquid chromatography .The high-performance liquid chromatography only uses packed analytical columns .Similarly, the gas chromatography method only uses capillary columns of fused silica coat. The columns in all cases are made of stainless steel.
List some advantages and important applications of SFC technique
Advantages of supercritical fluid chromatography include:
1. It does not require a concentrating procedure or a cleanup procedure before analysis.
2. It is applied for various compounds from different matrixes, including caffeine extraction, tocopherolenrichment, flavors extraction and analysis of pesticide residues
3. SFC is available to use for non-volatile or thermally unstable compounds when combined with FID
4. SFC is advantageous given that supercritical fluids have low viscosity therefore fast in analysis and the use of open tubular columns is feasible.
5. Another advantage of SFC is that it can be used with a wide range of sensitive detectors.
6. With SFC, it is possible to analyse solutes of much higher molecular weight.
7. It is also possible to analyse thermally labile compounds with SFC.
Applications of supercritical fluid chromatography;
1. Hypertensive patients’ diagnosis of the kidney fluids.
2. The method is used in the analysis of an aqueous solution of prostaglandins.
3. It has been used in analysis of fossil fuels and hydrocarbons in industries.

List of References

Graves, S.W. & Markides, K.E. 2000. Application of supercritical fluid chromatography to characterize a labile digitalis-like factor. Hypertension 36, pp.1059–1064.
King, J.W. & Hill, H.H. 1993. Analytical Supercritical Fluid Chromatography and Extraction. Peoria, Illnois: National Center for Agricultural Utilization Research. pp.2-41.
Mansoori, G.A. 2001. Supercritical Fluid Chromatography and Gel Permeation Chromatography for Characterization of Macromolecules. Chicago: University of Illnois, Department of Chemical Engineering. pp.2-30.

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