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Chromatography
Chromatography is a set of techniques used to separate mixtures in a chemistry lab setting. The word chromatography means "color writing" and some of the first experiments in chromatography involved separating chlorophyll in plants.
649 Questions
Is methanol a good solvent to use in paper chromatography?
Methanol is a commonly used solvent in paper chromatography because of its polarity and ability to dissolve a wide range of compounds. It is especially good for separating polar compounds. However, caution should be taken as methanol is also toxic and flammable.
Does polarity of a solvent mixture affect the completeness of the separation in chromatography?
Yes, the polarity of a solvent mixture can affect the completeness of the separation in chromatography. A more polar solvent mixture will tend to separate compounds with different polarities more effectively, leading to better resolution in the chromatogram. However, if the solvent mixture is too polar, it may cause poor separation or elution of certain compounds, affecting the completeness of the separation.
What is the root meaning of chromatography?
Chromatography comes from the Greek chrom- meaning "colored" and graph- meaning "writing" so it literally means "colored writing".
What happens when paper chromatography is left in the solution?
If paper chromatography is left in the solution, the solvent will continue to move up the paper by capillary action. This can lead to the separation of the components in the mixture to a greater extent. Additionally, the colors may spread out and further separate along the paper.
What is the difference between Chromatography and Spectrometry?
GCMS involves running the sample through a mass spectrometer following the data received from chromatography. MS fragments the analytes to show patterns specific to the analyte (and the ionization technique and sector powers) therefore allowing the analyte to be identified. GC is used to separate all volatile substituents of a sample so they can be identified one by one.
What does the technique of chromatography allows us to do?
Chromatography allows us to separate and analyze different components in a mixture based on their differential affinities for a stationary phase and a mobile phase. This technique is widely used in various fields such as chemistry, biochemistry, and forensic science for identifying and quantifying the components of complex mixtures.
Is chromatography physical change?
Chromatography is a physical change because even though you are separating colors the original atomic identity of the colored ink being separated is still retained showing that a chemical reaction has not taken place.
Are there risks when doing chromatography?
Yes, there are risks associated with chromatography. These can include exposure to harmful chemicals, inhalation of fumes, and potential fire hazards. It is important to follow proper safety procedures and use necessary protective equipment when conducting chromatography experiments.
The abilities of the compounds to absorb and their solubility are the physical properties used in the separation of components via chromatography. Boiling points are not typically used in chromatography, as the separation technique relies more on differences in absorption and solubility to separate compounds.
Paper chromatography Why must the spot be concentrated?
Keeping a small spot on TLC will allow for greater resolution between the spots allowing for more accurate Rf calculations and solvent separation/preparation if used to isolate a compound in a mixture.
Pen chromatography is a simple paper chromatography technique where a capillary pen is used to apply a small sample to filter paper. As the solvent moves up the paper, different components in the sample will separate into distinct bands based on their interactions with the paper and the solvent. This technique is often used for separating and identifying components of a mixture.
What is molecular exclusion chromatography?
Molecular exclusion chromatography is a type of size exclusion chromatography that separates molecules based on their size and shape. It works by passing a sample mixture through a porous stationary phase, where smaller molecules are able to enter the pores and take longer to elute, while larger molecules pass more easily through the column and elute faster. This technique is commonly used for separating proteins and nucleic acids.
What is the significance of Rf value in chromatography?
The Rf value, or retention factor, in chromatography is a measure of how far a compound travels in relation to the solvent front in a chromatogram. It helps in identifying and characterizing compounds based on their movement and separation in the chromatographic system. Comparing Rf values can aid in qualitative analysis, determination of purity, and identification of unknown components within a sample.
Difference between isothermal and isoperibol calorimeter?
In an isothermal calorimeter, the temperature inside the calorimeter remains constant during the measurement, preventing any heat exchange with the surroundings. In an isoperibol calorimeter, the calorimeter is well-insulated and allows heat exchange with the surroundings, but the heat loss or gain is accurately measured and compensated for.
Which dyes adhere best to chromatography paper?
Dyes that are more polar tend to adhere better to chromatography paper because they interact more strongly with the cellulose fibers in the paper. Therefore, water-soluble dyes like food coloring or ink tend to work well for paper chromatography.
These components would travel the farthest up the filter paper in chromatography because they are less attracted to the paper and more attracted to the solvent. They are likely to be found closer to the top of the paper where the solvent front has reached.
How to prepare 100 ppm solution of KMnO4?
I will assume that you will start from the crystals of permanganate:
Calculations:
M.M. potassium permanganate: 158.04 g/mol
mol KMnO4 in 10mL sol'n: 1.5 mol/L x 10 mL x (1 L / 1000 mL) = 0.015 mol
grams potassium permanganate: 0.015 mol x 158.04 g/mol = 2.3706 g / 10 mL sol'n
Preparation:
1. Weigh out analytically 2.3706g KMnO4 into a 10 mL volumetric flask.
2. Dilute to the mark with dH2O.
What detectors are used in HPLC?
The detector for an HPLC is the component that emits a response due to the eluting sample compound and subsequently signals a peak on the chromatogram. It is positioned immediately posterior to the stationary phase in order to detect the compounds as they elute from the column. The bandwidth and height of the peaks may usually be adjusted using the coarse and fine tuning controls, and the detection and sensitivity parameters may also be controlled (in most cases). There are many types of detectors that can be used with HPLC. Some of the more common detectors include: Refractive Index (RI), Ultra-Violet (UV), Fluorescent, Radiochemical, Electrochemical, Near-Infra Red (Near-IR), Mass Spectroscopy (MS), Nuclear Magnetic Resonance (NMR), and Light Scattering (LS). Refractive Index (RI) detectors measure the ability of sample molecules to bend or refract light. This property for each molecule or compound is called its refractive index. For most RI detectors, light proceeds through a bi-modular flow-cell to a photodetector. One channel of the flow-cell directs the mobile phase passing through the column while the other directs only the mobile phase. Detection occurs when the light is bent due to samples eluting from the column, and this is read as a disparity between the two channels.
Ultra-Violet (UV) detectors measure the ability of a sample to absorb light. This can be accomplished at one or several wavelengths:
A) Fixed Wavelength measures at one wavelength, usually 254 nm
B) Variable Wavelength measures at one wavelength at a time, but can detect over a wide range of wavelenths
C) Diode Array measures a spectrum of wavelengths simulateneously
UV detectors have a sensitivity to approximately 10-8 or 10 -9 gm/ml.
Fluorescent detectors measure the ability of a compound to absorb then re-emit light at given wavelengths. Each compound has a characteristic fluorescence. The excitation source passes through the flow-cell to a photodetector while a monochromator measures the emission wavelengths.
Has sensitivity limit of 10-9 to 10-11 gm/ml.
Radiochemical detection involves the use of radiolabeled material, usually tritium (3H) or carbon-14 (14C). It operates by detection of fluorescence associated with beta-particle ionization, and it is most popular in metabolite research. Two detector types:
A) Homogeneous- Where addition of scintillation fluid to column effluent causes fluorescence.
B) Heterogeneous- Where lithium silicate and fluorescence caused by beta-particle emission interact with the detector cell.
Has sensitivity limit up to 10-9 to 10-10 gm/ml.
Electrochemical detectors measure compounds that undergo oxidation or reduction reactions. Usually accomplished by measuring gain or loss of electrons from migrating samples as they pass between electrodes at a given difference in electrical potential.
Has sensitivity of 10-12 to 10-13 gm/ml
Mass Spectroscopy (MS) Detectors- The sample compound or molecule is ionized, it is passed through a mass analyzer, and the ion current is detected. There are various methods for ionization:
A) Electron Impact (EI)- An electron current or beam created under high electric potential is used to ionize the sample migrating off the column.
B) Chemical Ionization- A less aggresive method which utilizes ionized gas to remove electrons from the compounds eluting from the column.
C) Fast Atom Bombarbment (FAB)- Xenon atoms are propelled at high speed in order to ionize the eluents from the column.
Has detection limit of 10-8 to 10-10 gm/ml.
Nuclear Magnetic Resonance (NMR) Detectors- Certain nuclei with odd- numbered masses, including H and 13C, spin about an axis in a random fashion. However, when placed between poles of a strong magnet, the spins are aligned either parallel or anti-parallel to the magnetic field, with the parallel orientation favored since it is slightly lower in energy. The nuclei are then irradiated with electromagnetic radiation which is absorbed and places the parallel nuclei into a higher energy state; consequently, they are now in "resonance" with the radiation. Each H or C will produce different spectra depending on their location and adjacent molecules, or elements in the compound, because all nuclei in molecules are surrounded by electron clouds which change the encompassing magnetic field and thereby alter the absorption frequency.
Light-Scattering (LS) Detectors- When a source emits a parallel beam of light which strikes particles in solution, some light is reflected, absorbed, transmitted, or scattered. Two forms of LS detection may be used to measure the two latter occurrences:
A) Nephelometry- This is defined as the measurement of light scattered by a particulate solution. This method enables the detection of the portion of light scattered at a multitude of angles. The sensitivity depends on the absence of background light or scatter since the detection occurs at a black or null background.
B) Turbidimetry- This is defined as the measure of the reduction of light transmitted due to particles in solution. It measures the light scatter as a decrease in the light that is transmitted through the particulate solution. Therefore, it quantifies the residual light transmitted. Sensitivity of this method depends on the sensitivity of the machine employed, which can range from a simple spectrophotometer to a sophisticated discrete analyzer. Thus, the measurement of a decrease in transmitted light from a large signal of transmitted light is limited to the photometric accuracy and limitations of the instrument employed.
Near-Infrared Detectors- Operates by scanning compounds in a spectrum from 700 to 1100 nm. Stretching and bending vibrations of particular chemical bonds in each molecule are detected at certain wavelengths. This is a method which offers several advantages: speed (sometimes less than 1 second), simplicity of preparation of sample, multiple analyses from single spectrum, and nonconsumption of the sample.
What is the stationary phase in DB-624?
In DB-624, the stationary phase is a phenyl arylene polymer that has a 6% cyanopropyl substituent. This phase is commonly used in gas chromatography for separating a wide range of analytes, especially non-polar and moderately polar compounds.
What is carbon load in hplc column?
Carbon load is the percent by weight of carbon on the stationary phase. It measures how much organic material has been chemically attached to the surface of silica. For a reversed phase column, more carbon load usually means more retention for nonpolar compounds like protines. general rane of carbon load is 8-12%.
What is the principle behind the Gas Chromatography?
Gas is pushed threw a filimint gas is broken down into 4 gases and total gas so there is gas c1 c2 c3 c4 and tg or total gas so say 100 units of gas come in to a cromatograph 20 units burn at c1 level that means there is 20 units of c1 c2 level 30 units of gas burns away. I used to be a mud logger in the oilfields :) the most easy job i ever had 300 dollars a day for doing nothing :)
What happens in paper chromatography in inorganic ions?
In paper chromatography, inorganic ions can be separated based on their different affinities to the paper and mobile phase. As the mobile phase moves through the paper, ions with stronger affinities to the paper will move more slowly, causing them to separate from ions with weaker affinities. This differential migration will result in the separation of inorganic ions on the paper chromatogram.
The molar absorptivity of Cu2+ at 620 nm can be calculated using Beer-Lambert law equation A = εlc, where A is the absorbance, ε is the molar absorptivity, l is the pathlength (1.00 cm), and c is the concentration. Using the concentration- absorbance curve given (y = 0.727x + 0.0557), at 620 nm, x = c = 1. Therefore, substituting these values into the Beer-Lambert equation will give you the molar absorptivity of Cu2+ at 620 nm.
Mass spectrometer. The combination of gas chromatography and mass spectrometry (GC-MS) allows for the separation of compounds based on their physical properties in the gas chromatograph, followed by the specific identification of those compounds based on their mass-to-charge ratio in the mass spectrometer. This coupling provides enhanced specificity and sensitivity in compound identification compared to using gas chromatography alone.
What is the difference between absorption and emission spectrum?
Emission spectrum: lines emitted from an atom.
Absorption spectrum: absorbed wavelengths of a molecule.
