Quiz 3 - chapters 7, 8, 9

Why are atomic emission methods with an inductively coupled plasma source better suited for multielement analysis than are flame atomic absorption techniques?

Atomic emission methods using an inductively coupled plasma (ICP) source are better for analyzing multiple elements in a sample than flame atomic absorption techniques. ICP's high temperature makes it easier to detect a wide range of elements, and it can analyze several elements at once, saving time. It can detect very small amounts of elements, works for both low and high concentrations, and has fewer interferences, ensuring more accurate results. Overall, ICP makes multielement analysis simpler, faster, and more reliable compared to flame atomic absorption techniques.

Why is atomic emission more sensitive to flame stability than atomic absorption?

Atomic emission spectroscopy (AES) relies on the intensity of emitted light from a sample, making it more sensitive to flame stability compared to atomic absorption spectroscopy (AAS), which measures the absorption of light by the sample.

In which technique, atomic absorption or atomic emission, is flame temperature stability more critical? Why?

Atomic emission- When we analyze a sample using atomic emission spectroscopy, we're looking at the light given off by the atoms in the sample when they're excited. This light tells us what elements are present. To make this happen, we need to heat up the sample in a flame. If the flame temperature keeps changing, it can mess up the excitement process and the light we see, leading to wrong conclusions about the elements present in the sample.

What affect does atomization temperature have on AA spectroscopy and why? Answer as completely as possible (consideration such factors as ionization, molecular interferences, and atomic emission.

Atomization Efficiency: Higher temperatures lead to better conversion of the sample into free atoms, improving sensitivity. Ionization: Very high temperatures can cause some atoms to become ionized, reducing sensitivity. Molecular Interferences: Control of temperature helps minimize interference from molecules, ensuring accuracy. Atomic Emission: Excessive temperatures can induce unwanted emission, interfering with the analysis.

Understand the role band and continuum spectra play in atomic spectroscopy. (see section 8A-4, page 203)

Band Spectra: These result from transitions between molecular energy levels, appearing as broad, overlapping bands rather than distinct lines. Continuum Spectra: They consist of a continuous range of wavelengths with varying intensities, often from thermal emission or scattering. Both can affect the accuracy of the analysis, so minimizing their impact is important for reliable results.

Why is it so critically important to control flame temperature in flame atomic absorption spectroscopy?

Controlling flame temperature is crucial in flame atomic absorption spectroscopy (AAS) because it directly affects how well the sample is turned into atoms for analysis. It ensures better sensitivity, accuracy, and minimizes interferences, resulting in reliable measurements.

Why must the height of the burner head be adjusted each time a new analyte is examined with flame AA?

Different parts of the flame have different temperatures and oxidizing/reducing agents We want the most atomic species with the least excited atoms or ions

What is the effect of temperature on atomic spectra?

Doppler Broadening: When things get hotter, atoms move faster. This makes the lines in the spectra wider because the light they emit or absorb gets stretched or squished more due to their motion. Population Distribution: With higher temperatures, more atoms get excited to higher energy levels. This can make spectral lines broader or more intense because there are more transitions happening between energy levels. Thermal Radiation: Hotter temperatures mean more thermal radiation, which can add background noise to the spectra. This can make it harder to see the spectral lines clearly, especially at lower temperatures where the thermal radiation is stronger relative to the signal from the atoms. Collisional Broadening: When atoms collide more often, like at higher temperatures, it can mess with their energy levels, making spectral lines broader. This effect is more noticeable at higher temperatures and pressures.

Describe the processes that occur during flame atomization. (Use Figure 9.1 as your guide)

During flame atomization in atomic absorption spectroscopy (AAS), the liquid sample is sprayed into a flame where it quickly turns into gas. This gas contains the atoms of the element being analyzed. These atoms then absorb light at specific wavelengths, which we measure to find out how much of the element is in the sample. So, flame atomization is about turning the liquid sample into gas so we can analyze it.

Draw a block diagram of atomic absorption spectrophotometer? How does this is different that atomic fluorescence block diagram? How does this is different that atomic emission block diagram?

Emission: no external light source Flame Atomic Absorbance: external light source present Fluorescence: 90* external light source present

Be familiar with the various methods used to introduce samples into an atomic absorption instrument. Section 8-C)

Flame Atomization: Liquid samples are vaporized in a flame. Electrothermal Atomization: Solid or liquid samples are heated gradually in a graphite furnace. Hydride Generation: Some elements are converted into volatile hydrides before analysis. Cold Vapor Generation: Certain elements like mercury are turned into vapor at room temperature.

Describe the various techniques used for atomization in atomic spectroscopy.

Flame Atomization: Sample is vaporized in a flame. Electrothermal Atomization: Sample is heated slowly and evenly. Hydride Generation: Certain elements are converted into volatile hydrides. Cold Vapor Generation: Elements like mercury are turned into vapor at room temperature. Plasma Atomization: Sample is atomized at very high temperatures in plasma sources like ICP or microwave-induced plasma.

Be familiar with the various atomization techniques described in section 9A.

Flame Atomization: The liquid sample is vaporized in a flame. Electrothermal Atomization: The sample is heated slowly and evenly using electricity. Plasma Atomization: Samples are atomized at very high temperatures in plasma sources. Hydride Generation: Some elements are turned into volatile hydrides before analysis. Cold Vapor Generation: Certain elements like mercury are turned into vapor at room temperature.

What are some of the common interferences encountered in AA and what measures are used to minimize these interferences? (Section 9C)

In atomic absorption spectroscopy (AA), common interferences include overlapping absorption lines, chemical reactions with other compounds in the sample, and effects from the sample's makeup. interferences can be reduced by adjusting the background, using standard addition, selecting the appropriate wavelength, employing chemical modifiers, diluting or preparing the sample, and creating calibration curves.

Describe the various techniques used for atomic emission spectroscopy

Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES): A super-hot plasma vaporizes the sample, making atoms emit light. By looking at this light, scientists can figure out what elements are in the sample. Flame Emission Spectroscopy: A flame makes atoms in the sample emit light. By studying this light, scientists can tell which elements are present. Spark or Arc Emission Spectroscopy: Sparks or arcs between electrodes excite atoms in the sample, making them emit light. This light helps identify the elements in the sample, especially useful for solids. Glow Discharge Optical Emission Spectroscopy (GD-OES): A low-pressure glow makes atoms on a surface emit light. Analyzing this light reveals the elements on the surface. Laser-Induced Breakdown Spectroscopy (LIBS): A powerful laser creates a tiny explosion on the sample, making atoms emit light. Scientists use this light to quickly identify the elements in the sample.

Be very familiar with Section 8A "Optical Atomic Spectra" since this relatively small section provides the theoretical background necessary to understand optical atomic spectroscopy and some important properties of optical spectra!!!!!!!!!!!!

Line Spectra: Discrete lines in emission or absorption corresponding to atomic energy transitions. Continuous Spectra: A broad range of wavelengths without discrete lines, often from thermal radiation. Band Spectra: Broad, overlapping bands from transitions between molecular energy levels. Absorption Spectra: Dark lines on a continuous spectrum background from light absorption by atoms or molecules. Emission Spectra: Bright lines against a dark background from light emitted by excited atoms or molecules.

Describe the sources of line broadening of atomic line widths.

Natural Broadening: This happens because of the inherent uncertainty in the energy levels of atoms. It creates a symmetric line shape. Doppler Broadening: This occurs because atoms are moving around randomly due to heat. As they move toward or away from us, the light they emit or absorb gets stretched or squished, making the lines wider. Pressure Broadening: When atoms collide with other particles, like gas molecules, it can mess with their energy levels, making the lines wider. Stark Broadening: This happens when atoms interact with electric fields, like those in plasmas or electric discharges. It also makes the lines wider. Instrumental Broadening: Sometimes, the equipment we use to measure the spectra isn't perfect. Imperfections in the instruments can also make the lines wider.

Which technique is more sensitive, flame AA or atomic emission spectroscopy and why? (Hint- this is a trick question)

Neither, it depends on the circumstances.

Describe the processes that occur in electrothermal atomization.

Sample Drying: The sample solution is heated to remove any liquid and concentrate the analyte. Pyrolysis: Organic compounds in the sample break down into simpler forms, removing unwanted substances. Atomization: The sample is heated to very high temperatures, turning it into atoms or ions that can be detected. Detection: The atoms or ions are carried to a detector where their presence is measured, allowing for analysis of the sample's composition.

Describe the processes involved in sample introduction and atomization in flame AA. (Use Figure 9.1 as your guide)

Sample Introduction: The sample introduction process involves delivering the sample into the flame for analysis. This can be done using various methods, such as a nebulizer or an aspirator.a. Sample Delivery: The sample is introduced into the flame typically through a nebulizer, where it is converted into a fine mist or aerosol. This mist is then carried into the flame by a stream of inert gas, such as argon or nitrogen, through a spray chamber.b. Spray Chamber: The spray chamber helps to further break down the sample into smaller droplets and removes larger particles or droplets before they enter the flame. This ensures a consistent and uniform sample delivery to the flame. Atomization: Atomization is the process of converting the sample into individual atoms in the gas phase, which is necessary for absorption to occur. This process occurs within the flame.a. Desolvation: As the sample mist enters the flame, the solvent (if present) evaporates, leaving behind solid or dissolved analyte particles.b. Drying: The remaining particles undergo further drying as they travel through the flame, removing any residual solvent and reducing the sample to a dry residue.c. Vaporization: The dry sample residue is then heated within the flame to vaporize the analyte atoms. The intense heat of the flame causes the atoms to transition from their ground state to an excited state.d. Atomization: Finally, the excited atoms are thermally atomized, meaning they break apart into individual, neutral atoms. These neutral atoms are then present in the flame at elevated temperatures.

What is the difference between a simultaneous and sequential ICP and what are the advantages and disadvantages of each technique?

Simultaneous ICP is faster and suitable for routine analysis of samples with multiple elements, but it might have lower sensitivity and limited dynamic range. Sequential ICP provides higher sensitivity and wider dynamic range, making it suitable for samples with low concentrations or wide concentration ranges, but it's slower and more complex to operate.

Describe the various interferences in atomic absorption spectroscopy and what is done to minimize these interferences.

Spectral interference: happens when the light absorbed by the thing we want to measure overlaps with the absorption of other stuff in the sample. It's like trying to listen to someone whispering in a noisy room—you might miss what they're saying because of all the other noise around. In AAS, this noise comes from other elements or compounds in the sample. Chemical interference: is when the elements or compounds in the sample chemically react with the thing we're trying to measure or affect its behavior in some way. It's like if you're trying to count how many candies you have, but someone keeps adding or taking away candies without you knowing—it messes up your count.

Discuss the temperature profile of a flame and how this profile affects the processes that go on in that flame relevant to flame atomic absorption and emission Spectroscopy.

Temperature Profile of a Flame: A flame has different temperature zones: the hottest part is the inner cone, followed by the secondary zone and the outer flame. Effects on Flame Atomic Absorption Spectroscopy (FAAS): In FAAS, the flame heats the sample, turning it into atoms for analysis. The hotter inner cone is where most of this atomization happens, providing optimal conditions for analysis. However, too much heat can cause background interference and noise in the results. Effects on Flame Atomic Emission Spectroscopy (FAES): In FAES, the flame heats the sample, causing it to emit light. The hottest part of the flame excites the atoms the most, resulting in stronger emission signals. But, this part of the flame also contributes to background noise.

Would the emission spectra of elemental sodium be the same of ionic sodium? Explain you answer. (little credit will be given for a simple yes or no answer) see section 8A-1.

The emission spectra of elemental sodium and ionic sodium would not be the same because they have different electronic configurations and energy levels. So, they produce different patterns of light when excited.

Why are ionization interferences less severe in ICP than in flame emission Spectroscopy?

The hotter temperatures and the way ions are formed in ICP make it less prone to ionization interferences compared to flame emission spectroscopy.

Describe the hydride generation process for atomic absorption spectroscopy. Why is this technique used rather than simply introducing the liquid sample into a flame?

The hydride generation process in atomic absorption spectroscopy converts certain elements into volatile hydrides before introducing them into the flame. This enhances sensitivity, reduces interferences, minimizes matrix effects, and improves safety compared to directly introducing the liquid sample into the flame.

Why do electrothermal atomizers generally provide higher sensitivities than flame Atomizers?

They are more sensitive than flame atomizers because they heat samples more slowly and evenly, leading to better atomization and stronger signals for analysis.

Describe the sources of line broadening of atomic line widths.

Uncertainty effect Doppler effect Pressure effects due to collisions between atoms of the same kind with foreign atoms Electric and magnetic fields

What determines natural line widths for atomic emission and absorption lines? About how broad are these widths, typically?

for atomic emission and absorption lines are determined by the uncertainty principle of quantum mechanics. Typically, these widths range from several megahertz to gigahertz, reflecting the inherent uncertainty in the energy of particles over time.

What is resonance fluorescence?

happens when an atom or molecule absorbs a photon at a specific frequency and then emits another photon at the same frequency.

How do hollow cathode tubes work?

have a metal cathode surrounded by argon gas. When electricity passes through, it makes the argon gas glow. This glow excites the metal atoms in the cathode, making them emit light. This emitted light helps analyze the metal's presence and amount in a sample.

The effective bandwidths of the lines emitted by AA lamps are significantly narrower than the corresponding bandwidths of the absorption peaks in flame AA. Why is this fact so critically important to the success of flame AA?

he narrower bandwidths of the lines emitted by AA lamps are important for flame AA because they make the analysis more accurate and sensitive. They help to distinguish the absorption signal of the element being measured from background noise and interference, improving the reliability of the results.

Name a continuous type and a discrete type of atomizer that are used in atomic spectrometry. How do the output signals from a spectrometer differ for each?

in flame atomizers, the signal is continuous with peaks, while in electrothermal atomizers, it shows discrete peaks.

Why is the internal standard method often employed in plasma emission Spectrometry?

is used in plasma emission spectrometry to make sure our measurements are accurate and reliable. It helps by compensating for changes in the sample's composition, correcting instrument drift, and improving the precision of our analysis. This method ensures that our results are consistent and trustworthy, even when working with complex samples.

What are natural lines widths for atomic emission and absorption lines and what is the cause of these line widths?

linewidths for atomic emission and absorption lines are very narrow, usually just a few nanometers wide. These narrow widths are primarily caused by the uncertainty principle, which states that there's an inherent uncertainty in the energy and lifetime of excited states in atoms. Additionally, the motion of atoms due to temperature, known as Doppler broadening, also contributes to the line width by causing slight shifts in the emitted or absorbed light frequencies.

Under what conditions can a Stokes shift (see Section 6C-6) occur in atomic spectroscopy?

occurs when emitted light has less energy than the absorbed light. This can happen when an electron moves to a higher energy level after absorbing a photon, and then emits a photon with lower energy during relaxation.

The intensity of a line for atomic Li is much lower in a natural gas flame, which operates at 1800°C, than in a hydrogen-oxygen flame, whose temperature is 2700°C. Explain.

the hydrogen-oxygen flame is hotter and provides more energy to excite lithium atoms, resulting in stronger emission compared to the natural gas flame.

In a hot flame, the emission intensities of the sodium lines at 589.0 and 589.6 nm are greater in a sample solution that contains KCl than when this compound is absent. Suggest an explanation.

the presence of KCl in the sample solution leads to increased emission intensities of sodium lines at 589.0 and 589.6 nm compared to when KCl is absent. This is likely due to the formation of sodium-potassium compounds in the flame, which enhances the emission of sodium lines.

What is the purpose of the flame in flame atomic absorption spectroscopy?

to turn the liquid sample into a gas. This gas contains the atoms of the element being analyzed. These atoms then absorb light at specific wavelengths, allowing us to measure their concentration in the sample. So, the flame essentially prepares the sample for analysis.