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

قد تواجه قياسات AAS تداخلات طيفية أو كيميائية أو فيزيائية تحجب أو تغير حجم إشارة التحليل المكتشفة.
يحدث التداخل الطيفي عندما تتداخل إشارة من متداخل أو لهب الانحلال مع إشارة المادة المراد تحليلها ، مما يؤدي إلى رفع أو إخفاء امتصاص المادة المراد تحليلها بشكل خاطئ.
يمكن معالجة ذلك باستخدام تقنيات Zeeman أو Smith-Hieftje أو deuterium لتصحيح الخلفية. بالإضافة إلى ذلك ، يمكن لمقاييس الطيف عالية الاستبانة أن تقلل من التداخل الطيفي من الخطوط الطيفية المتداخلة. 
تشمل مصادر التداخل الكيميائي تفاعلات التحليل مع مكونات المصفوفة ، مما ينتج عنه أملاح غير متطايرة تقلل من كفاءة الانحلال.
يمكن تجنب هذا التداخل باستخدام درجات حرارة الانحلال العالية أو عن طريق إضافة عوامل معقدة أو إطلاقة.
علاوة على ذلك ، قد تتأين بعض التحليلات الذرية أثناء التحليل ، مما يؤدي إلى انخفاض الامتصاص. ومع ذلك ، فإن إضافة عنصر متأين بسهولة تثبط تأين المادة التحليلية.
يتم تقليل التداخلات الفيزيائية الناشئة عن عوامل غير كيميائية ، مثل الاختلافات في معدلات تدفق الغاز أو درجة حرارة اللهب ، من خلال المعايرة المتكررة أو المعايير الداخلية أو إضافة كميات معروفة من المواد التحليلية إلى العينة.

التحليل الطيفي للامتصاص الذري: التداخل

Atomic Absorption Spectroscopy: Interference

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يؤدي التداخل إلى حدوث خطأ منهجي في قياسات الامتصاص الذري (AA) من خلال تعزيز أو تقليل الإشارة التحليلية أو الخلفية. يمكن تصنيف هذه التداخلات إلى ثلاث فئات رئيسية: التداخل الطيفي، والتداخل الكيميائي، والتداخل الفيزيائي.

يحدث التداخل الطيفي عندما تتداخل الإشارات من عناصر أو جزيئات أخرى مع إشارة المحلل، مما يؤدي إلى زيادة أو تقليل خاطئ في امتصاص المحلل. يمكن تصحيح هذا التداخل باستخدام طرق تصحيح الخلفية مثل طريقة زيمن أو سميث-هايفتي أو طريقة مصباح الديوتيريوم.

تستخدم طريقة تصحيح زيمان مجالًا مغناطيسيًا لتقسيم خط الامتصاص إلى ثلاثة مكونات مستقطبة: اثنان σ (مُزاحان) وواحد π (غير مُزاح). يتم قياس امتصاص المحلل والخلفية بشكل منفصل عن طريق تبديل المجال المغناطيسي، مما يعزز الدقة في المصفوفات المعقدة.

تعتمد طريقة تصحيح سميث-هايفتي على نبض مصباح الكاثود المجوف (HCL) عند تيارات عالية، مما يتسبب في اتساع خط الانبعاث وخضوعه للانعكاس الذاتي، حيث يتضاءل خط التحليل المركزي. يؤدي هذا إلى انبعاث قوي على جانبي الخط، تمتصه الخلفية. يتم قياس الامتصاص في ظل الظروف العادية والتيار العالي، مما يسمح بالتمييز بين إشارات المحلل والخلفية. على الرغم من أن هذه الطريقة تتطلب مصدر ضوء واحد فقط، فإن حساسية الطريقة تنخفض، خاصة عندما يكون الانعكاس الذاتي غير كافٍ أو يكون الاسترداد بطيئًا للغاية.

تستخدم طريقة تصحيح خلفية الديوتيريوم (D_2) مصباح D_2 كمصدر ضوء واسع الطيف لتصحيح امتصاص الخلفية في مطيافية الامتصاص الذري (AAS). يتم استخدام مرآة دوارة للتبديل بين مصباح الكاثود المجوف ضيق النطاق (HCL) ومصباح D_2 عريض النطاق. يقيس مصباح D_2 امتصاص الخلفية عبر نطاق واسع من الطول الموجي، بينما يقيس مصباح HCL امتصاص المحلل والخلفية عند طول موجي محدد. إن الفرق بين الإشارتين يعزل امتصاص المحلل. رغم أن هذه الطريقة غير مكلفة، إلا أنه يفتقر إلى الدقة في القياسات عالية الدقة.

بالإضافة إلى ذلك، يمكن لأجهزة قياس الطيف عالية الدقة تقليل التداخل الطيفي الناتج عن الخطوط الطيفية المتداخلة. في بعض الأحيان، يمكن استخلاص المحلل بشكل متكرر باستخدام مذيب قبل التحليل.

تحدث التداخلات الكيميائية عندما تتفاعل مكونات المصفوفة غير المرغوب فيها مع المحلل، مما يقلل من كفاءة التذرية. يمكن إضافة معدِّل كيميائي، مثل عامل تحرير أو عامل تكوين معقد، إلى العينة لتعزيز التذرية أو منع تكوين المركبات المتداخلة. تشمل التداخلات الكيميائية الشائعة التداخلات الناتجة عن التأين وتكوين المركبات المقاومة للحرارة.

يمكن للعناصر أو المركبات التي تتأين عند نفس درجة حرارة المحلل أن تغير تأينه. يمكن قمع التأين عن طريق إضافة فائض من المحلول الذي يحتوي على عنصر يتأين بسهولة أكبر، مما يقلل من تأين المحلل.

علاوة على ذلك، يمكن أن تؤدي التفاعلات الكيميائية بين المحلل والأنواع الأخرى في مصفوفة العينة إلى تكوين مركبات غير متطايرة لا تتحول إلى ذرات بسهولة. وهذا يعيق تكوين الذرات الحرة للامتصاص. يتم تجنب مثل هذا التداخل عن طريق إضافة منافس كيميائي أو استخدام درجات حرارة عالية جدًا.

يمكن تحضير معايير المعايرة باستخدام مصفوفة عينة مماثلة للعينات الحقيقية، مما يساعد في تعويض التداخلات الكيميائية الناشئة عن المصفوفة.

تؤثر التداخلات الفيزيائية الناشئة عن عوامل غير كيميائية، مثل تغيرات معدل تدفق الغاز أو تغيرات درجة حرارة اللهب، على عملية الرش أو التذرية. يمكن حل هذه التداخلات باستخدام معايير داخلية أو تخفيف العينة. يمكن أن يؤدي تعديل مصفوفات العينة وتحضير معايير المعايرة باستخدام مصفوفة مماثلة إلى تقليل التداخلات الفيزيائية بشكل أكبر.
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يؤدي التداخل إلى خطأ منهجي في قياسات الامتصاص الذري (AA) عن طريق تحسين أو تقليل الإشارة التحليلية أو الخلفية. هذه...

atomic-absorption-spectroscopy-interference

Education

JoVE Core

Analytical Chemistry

الكيمياء التحليلية

Unit 1

الوحدة الأولى

Atomic Spectroscopy

المطيافية الذرية

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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 absorbance. It can be reduced with Zeeman, Smith-Hieftje, or deuterium background correction methods. High-resolution spectrometers can also help minimize overlap from nearby spectral lines, and in some cases the analyte can be repeatedly extracted with a solvent before analysis.

The Zeeman correction method uses a magnetic field to split the absorption line into three polarized components. Two are shifted sigma components, and one is an unshifted pi component. The analyte and the background are measured separately by alternating the magnetic field, which improves accuracy in complex samples. The Smith-Hieftje method uses a hollow cathode lamp at high current. This broadens the emission line and causes self-reversal, where the central analytical line decreases. Strong emission remains on both sides of the line and is absorbed by the background. Absorbance is measured under normal and high-current conditions to separate analyte and background signals, but sensitivity can drop if self-reversal is weak or recovery is slow. The deuterium background correction method uses a D2 lamp as a broad-spectrum light source. A rotating mirror switches between the narrow-band hollow cathode lamp and the broad-band D2 lamp. The D2 lamp measures background absorbance over a wide wavelength range, while the hollow cathode lamp measures analyte and background absorbance at one wavelength. The difference between the two signals isolates the analyte absorbance, although this method is less precise in high-accuracy work.

Chemical interferences occur when matrix components in the sample react with the analyte and reduce atomization efficiency. A chemical modifier, such as a releasing agent or complexing agent, can be added to improve atomization or prevent interfering compounds from forming. Common chemical problems include ionization interference and refractory compound formation. If another element or compound ionizes at the same temperature as the analyte, it can change the analyte ionization. This can be suppressed by adding an excess of an element that ionizes more easily. Chemical reactions can also form nonvolatile compounds that do not atomize easily, which limits free atom formation for absorption. Adding a chemical competitor or using very high temperatures can help prevent this. Matching the calibration standards to the sample matrix also helps correct for matrix effects.

Physical interferences come from non-chemical changes, such as gas flow rate changes or flame temperature changes. These factors can affect nebulization or atomization. They can be reduced with internal standards, sample dilution, and matrix matching. Preparing calibration standards with a similar matrix can also help reduce physical interference and improve measurement reliability.

Correcting Errors in Atomic Absorption Spectroscopy

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atomic spectroscopy: absorption, emission, and fluorescence

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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...

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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...

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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

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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

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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

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Atomic Absorption Spectroscopy: Sample Atomization

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atomic absorption spectroscopy: interference

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...

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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...

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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

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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

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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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inductively coupled plasma atomic emission spectroscopy: instrumentation

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ICP-AES Instrument Types and Detection

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Flame Emission Spectrometry Basics

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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 spectral, chemical, and physical interference affect atomic absorption spectroscopy and how background correction helps improve accuracy.

Correcting Errors in Atomic Absorption Spectroscopy | JoVE K12

analytical chemistry

JoVE Core Analytical Chemistry simplifies complex chemical principles by breaking them down into clear, engaging animations, making topics from SI Units to NMR spectroscopy more accessible and straightforward. Additionally, the scientist-in-action videos highlight the application of these concepts in real-world research conducted in laboratories globally.

Correcting Errors in Atomic Absorption Spectroscopy

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