Name: atomic absorption spectroscopy: sample atomization
Uploaded: 2024-12-05T18:32:14.000Z
Duration: 1 min 25 s
Channel: JoVE

AAS zwykle rozpyla próbki poprzez atomizację płomieniową lub elektrotermiczną.
Atomizacja płomieniowa zazwyczaj wykorzystuje nebulizator do ciągłego aerozolu próbki i zespół komory natryskowej do mieszania jej z paliwem i utleniaczem.
Tylko około pięciu procent kropelek aerozolu jest wystarczająco drobnych, aby dotrzeć do płomienia, gdzie rozpuszczają się w pierwotnej strefie spalania, pozostawiając gołe cząstki, które są rozpylane w wewnętrznym płomieniu.
Gazowe atomy, jony i cząsteczki szybko przepływają przez obszar międzystrefowy w celu analizy i wydostania się z płomienia.
Ponieważ bardzo niewielka część próbki jest skutecznie rozpylana i wykrywana, atomizacja płomieniowa nie jest dobra w przypadku próbek o niskich stężeniach analitu lub ograniczonych objętościach.
Z drugiej strony atomizacja elektrotermiczna, znana również jako atomizacja w piecu grafitowym, wykorzystuje rurkę grafitową do wychwytywania i koncentrowania analitów z małych, dyskretnych próbek, które są suszone, zwęglone i atomizowane w wysokich temperaturach.
Alternatywnie, niektóre pierwiastki w łagodniejszych warunkach chemicznych najpierw przekształcają się w lotne produkty wodorkowe, a następnie mogą być rozpylane. Ponadto oznaczanie rtęci może odbywać się przy użyciu unikalnej metody zimnej pary ze względu na jej naturalną lotność.

spektroskopia absorpcji atomowej: metody atomizacji

Atomic Absorption Spectroscopy: Atomization Methods

Spektroskopia absorpcji atomowej (AAS) atomizuje próbki za pomocą atomizacji płomieniowej lub elektrotermicznej. Atomizacja płomieniowa zazwyczaj wykorzystuje nebulizator i komorę rozpylania, które łączą próbkę z mieszanką paliwowo-utleniającą, tworząc drobną mgłę aerozolową wprowadzającą próbkę do palnika. Paliwo i utleniacz są zazwyczaj mieszane w stosunku zbliżonym do stechiometrycznego. Jednak dla pierwiastków łatwo utleniających się korzystniejsze może być zastosowanie mieszanki bogatej w paliwo. Tylko około 5% kropelek aerozolu dociera do płomienia, gdzie ulegają odsolwatowaniu w strefie pierwotnego spalania, pozostawiając cząstki, które są atomizowane w wewnętrznej części płomienia. Gazowe atomy, jony i cząsteczki szybko przechodzą przez obszar między strefami, gdzie są analizowane, zanim opuszczą płomień. Atomizatory płomieniowe charakteryzują się niską wydajnością atomizacji ze względu na to, że duże krople aerozolu nie docierają do płomienia, a gazy powstające podczas spalania znacząco rozcieńczają próbkę. Wydajność atomizacji płomieniowej można jednak poprawić poprzez ciągłe zasysanie próbki, optymalizację stosunku paliwa do utleniacza, regulację przepływu przez nebulizator oraz ustawienie odpowiedniej wysokości palnika.

Atomizacja płomieniowa nie nadaje się do próbek o niskim stężeniu analitu lub ograniczonej objętości ze względu na małą liczbę próbek pomyślnie rozpylonych i wykrytych. Natomiast atomizacja elektrotermiczna, znana również jako atomizacja w piecu grafitowym, wykorzystuje rurkę grafitową do wychwytywania i zagęszczania analitów i dobrze sprawdza się w przypadku małych, dyskretnych próbek. W tej technice próbka jest suszona i zwęglana przed rozpyleniem w wysokich temperaturach.

 Pierwiastki takie jak As, Se, Sb, Bi, Ge, Sn, Te i Pb można rozpylać w łagodniejszych warunkach poprzez chemiczną konwersję do lotnych wodorotlenków przed przeniesieniem ich do płomienia. Ponadto, oznaczanie rtęci może wykorzystywać unikalną metodę zimnej pary ze względu na jej naturalną lotność.

Spektroskopia absorpcji atomowej: metody atomizacji

Atomowa spektroskopia absorpcyjna (AAS) rozpyla próbki poprzez atomizację płomieniową lub atomizację elektrotermiczną. Atomizacja płomieniowa zazwyczaj obejmuje ...

atomic-absorption-spectroscopy-atomization-methods

Education

JoVE Core

Analytical Chemistry

Chemia analityczna

Unit 1

Jednostka 1

Atomic Spectroscopy

Spektroskopia atomowa

KEY TERMS AND CONCEPTS

KLUCZOWE TERMINY I POJĘCIA

atomic absorption spectroscopy: sample atomization

Atomic absorption spectroscopy uses sample atomization to turn a liquid specimen into free atoms for analysis. The two main approaches are flame atomization and electrothermal atomization. Both methods prepare the sample so its atoms can be measured by the instrument.

Flame atomization uses a nebulizer and spray chamber to mix the sample with a fuel-oxidant mixture. This creates a fine aerosol mist that enters the burner. The fuel and oxidant are usually close to a stoichiometric ratio, but a fuel-rich mixture can work better for atoms that oxidize easily.

Only about 5% of the aerosol droplets reach the flame. In the primary combustion zone, these droplets undergo desolvation, which means the solvent is removed. The bare particles are then atomized in the inner flame. The gaseous atoms, ions, and molecular species move through the interzonal region for analysis before leaving the flame.

Flame atomizers have low atomization efficiency. Large droplets do not reach the flame, and combustion gases also dilute the sample. Efficiency can be improved by continuously aspirating the sample, adjusting the fuel-to-oxidant ratio, changing the nebulizer flow rate, and setting the burner height. Flame atomization is not a good choice for samples with very low analyte levels or small sample volumes.

Electrothermal atomization, also called graphite furnace atomization, uses a graphite tube to collect and concentrate the analytes. It works well for small, discrete samples. The sample is first dried and charred, then atomized at very high temperatures.

Some elements, including As, Se, Sb, Bi, Ge, Sn, Te, and Pb, can be handled under milder conditions by forming volatile hydrides before they are carried to the flame. Mercury can also be measured with a cold-vapor method because it is naturally volatile.

Atomic Absorption Spectroscopy: Sample Atomization

atomic-absorption-spectroscopy-sample-atomization

atomic spectroscopy: absorption, emission, and fluorescence

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Element Analysis with Atomic Light Spectra

Atomic spectroscopy is used to identify and measure elements by their light signals. It supports both qualitative analysis, which tells what is present, and quantitative analysis, which tells how much is present. The optical methods in this group are atomic absorption spectroscopy, atomic emission spectroscopy, and atomic fluorescence spectroscopy. These methods begin with atomization. In this step, a solid, liquid, or solution sample is changed into gas-phase atoms and ions. Once the sample...

atomic spectroscopy: effects of temperature

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How Heat Changes Atomic Spectra

Heat changes atomic spectra by affecting atomization, excitation, ionization, and line shape. In atomic spectroscopy, atomization means converting a sample into gas-phase atoms and ions. The flame temperature needed for this step changes how efficiently the method works and shifts the balance between excited and ground-state atoms. At thermal equilibrium, the relative numbers of excited and ground-state atoms can be estimated with the Maxwell-Boltzmann distribution. A small temperature rise...

atomic absorption spectroscopy: overview

Atomic Absorption Spectroscopy for Trace Metals

Atomic absorption spectroscopy (AAS) measures trace metals by tracking how atoms absorb electromagnetic radiation (EMR). The absorbed light makes atoms move to a higher-energy orbit. In AAS, the key step is atomization, which converts the sample into gas-phase atoms. A flame or a furnace is typically used for this step. Inside the flame, some atoms become thermally excited. Most stay in the ground state, which is the lowest-energy state. These ground-state gas-phase atoms absorb EMR only when...

atomic absorption spectroscopy: instrumentation

atomic-absorption-spectroscopy-instrumentation

Atomic Absorption Spectroscopy: Key Parts

Atomic absorption spectrophotometry uses a set of key parts to measure light absorbed by atoms. The main components are a radiation source, an atomizer, a monochromator, and a detector. Each part has a specific job in the instrument. The radiation source is usually a hollow-cathode lamp, or HCL, or an electrodeless-discharge lamp, or EDL. Both produce a narrow emission line at the needed wavelength. Some instruments instead use continuum sources with high-resolution monochromators to narrow...

atomic absorption spectroscopy: radiation and light sources

atomic-absorption-spectroscopy-radiation-and-light-sources

Choosing Light Sources for AAS Measurements

Atomic absorption spectroscopy (AAS) uses a light source that emits a very narrow range of wavelengths. This is needed because the source must match the absorption behavior of the analyte atom. The choice of source also depends on giving a precise, intense emission at the right wavelength for accurate detection. Two common line sources in AAS are hollow-cathode lamps (HCLs) and electrodeless-discharge lamps (EDLs). These lamps are selected based on the element being analyzed and the level of...

atomic absorption spectroscopy: atomization methods

Atomic absorption spectroscopy uses sample atomization to turn a liquid specimen into free atoms for analysis. The two main approaches are flame atomization and electrothermal atomization. Both methods prepare the sample so its atoms can be measured by the instrument. Flame atomization uses a nebulizer and spray chamber to mix the sample with a fuel-oxidant mixture. This creates a fine aerosol mist that enters the burner. The fuel and oxidant are usually close to a stoichiometric ratio, but a...

atomic absorption spectroscopy: interference

atomic-absorption-spectroscopy-interference

Correcting Errors in Atomic Absorption Spectroscopy

Atomic absorption spectroscopy interference can create systematic error by making the analytical signal or the background look stronger or weaker than it should be. In atomic absorption measurements, these errors are usually grouped as spectral interference, chemical interference, and physical interference. Spectral interference happens when signals from other elements or molecules overlap with the analyte signal, the substance being measured. This overlap can falsely raise or hide the analyte...

atomic absorption spectroscopy: lab

AAS Sample Prep and Calibration

Atomic absorption spectroscopy (AAS) depends on careful sample preparation and calibration. Samples must be turned into clear solutions before measurement. That often means extra treatment to dissolve materials such as soils, animal tissues, and minerals. Common sample prep methods include hot mineral acids, wet ashing, combustion in closed containers, high-temperature ashing, and fusion with reagents. These steps help make the sample suitable for AAS analysis. Solutions that contain organic...

atomic emission spectroscopy: overview

Atomic Emission Spectroscopy for Element Analysis

Atomic emission spectroscopy is used to identify the elements in a sample by measuring the light they emit. Atoms are first excited to higher energy levels by thermal energy from hot sources such as plasma, arcs, or sparks. When they fall back to lower energy levels, they give off light at specific wavelengths. Each element produces its own set of lines, so the emission spectrum can show both what is present and how much is there. AES instruments are similar to atomic absorption spectrometers,...

atomic emission spectroscopy: instrumentation

atomic-emission-spectroscopy-instrumentation

AES Sample Handling and Detection

Atomic emission spectrometry (AES) uses sample handling, atomization, and detection parts to measure emitted light from atoms and ions. The sample must first be changed into a gas-phase form so it can produce a measurable signal. AES uses two main atomizer types. Continuous atomizers, such as flames and plasmas, feed the sample in a steady stream. Discrete atomizers add one sample at a time with syringes or autosamplers. The electrothermal atomizer is the most common discrete type. Many...

atomic emission spectroscopy: interference

atomic-emission-spectroscopy-interference

Reducing Interference in AES Signals

Atomic emission spectroscopy (AES) can produce interfering signals when atoms and molecules in a flame or plasma emit overlapping light. High-temperature atomizers excite many species at once, including oxides, hydroxides, and flame combustion products. These extra emissions can make the analyte signal harder to read. Spectral interference happens when emission lines or bands overlap. One way to reduce it is to improve instrument resolution. Another is to choose a different emission line for...

inductively coupled plasma atomic emission spectroscopy: principle

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ICP-AES Torch and Sample Analysis

Inductively coupled plasma atomic emission spectroscopy uses a plasma torch to analyze elements in a sample. This method is also called inductively coupled plasma optical emission spectroscopy, or ICP-OES. It is widely used because the plasma creates a strong environment for elemental analysis. The ICP source, or torch, contains three concentric quartz tubes. Argon gas flows through the tubes. A spark from a Tesla coil starts the ionization of argon and creates a high-temperature plasma. The...

inductively coupled plasma atomic emission spectroscopy: instrumentation

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ICP-AES Instrument Types and Detection

Inductively coupled plasma atomic emission spectroscopy, or ICP-AES, uses an inductively coupled plasma to detect and analyze elements in a sample. The method measures the light given off by atoms, which helps identify and compare different elements. It is a common approach in atomic emission spectroscopy. ICP-AES instruments are built in three main forms: sequential, simultaneous multichannel, and Fourier transform instruments. Fourier transform designs are less commonly used, but they are...

atomic emission spectroscopy: lab

Plasma Sources in Atomic Emission Spectroscopy

Atomic emission spectroscopy uses plasma sources to identify elements by their light. The method creates abundant spectra with characteristic emission lines. Inductively coupled plasma, or ICP, is especially useful because it gives strong quantitative data. It works well under stable conditions, with low noise, low background, and few interferences. Newer air-operated microwave sources are also being studied. These sources may be more cost-effective than conventional ICP systems. Atomic...

atomic fluorescence spectroscopy

Measuring Elements by Atomic Fluorescence

Atomic fluorescence spectroscopy measures elements by detecting the light atoms give off after they are excited by electromagnetic radiation. The atoms are first placed in a flame, furnace, or plasma. They absorb energy, become excited, and then release that energy as they return to their original state. The emitted light is called fluorescence. The fluorescence is observed at a right angle to the incoming beam. This setup helps separate the emitted light from the light used to excite the...

flame photometry: overview

Flame Emission Spectrometry Basics

Flame emission spectrometry uses a flame to excite elements in a sample so their light can be measured. It is also called flame photometry. The method can be used for both qualitative and quantitative analysis of elements. The idea became established in the early 1860s when Kirchhoff and Bunsen showed that specific elements give off characteristic radiation in a flame. The first instrument for this purpose measured sodium in plant ash with a Bunsen flame. A major problem was how to add the...

flame photometry: lab

Flame Photometry and Metal Detection

Flame photometry is a method for detecting metals by measuring the light they emit in a flame. A solution such as potassium chloride is aspirated into the flame. The solvent evaporates first. The remaining salt becomes dehydrated and then dissociates into free gaseous atoms in the ground state. Some of these atoms absorb energy from the flame and move to an excited state. When they return to the ground state, they emit photons at characteristic wavelengths. These emissions are very narrow...

key terms and concepts

Learn how AAS atomizes samples with flame and graphite furnace methods, plus hydride and cold-vapor techniques for specific elements.

Atomic Absorption Spectroscopy: Sample Atomization | JoVE K12

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Atomic Absorption Spectroscopy: Sample Atomization

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