Name: luminol chemiluminescence in forensics
Uploaded: 2020-03-26T07:22:29.000Z
Duration: 3 min 2 s
Channel: JoVE

Zwykle, gdy reagenty zmieniają się w produkty, różnica w ich energii jest znana jako entalpia reakcji, która może być egzotermiczna, w której uwalniane jest ciepło, lub endotermiczna, w której ciepło jest pochłaniane.
W reakcji chemiluminescencyjnej reagenty tworzą produkt pośredni, który znajduje się w stanie wzbudzonym elektronicznie. Ten produkt pośredni jest niestabilny. Gdy rozluźnia się do stanu podstawowego, elektrony w półprodukcie uwalniają energię w emisji światła widzialnego, a nie w postaci ciepła.
Zjawisko to jest podobne do fluorescencji. Przypomnij sobie, że elektrony w cząsteczce zajmują stan podstawowy. Kiedy absorbują energię, na przykład pod wpływem określonej długości fali światła, stają się wzbudzone i przechodzą na wyższy, wzbudzony poziom energii. Gdy stan wzbudzony rozluźnia się z powrotem do stanu podstawowego, nadmiar energii jest emitowany w postaci światła widzialnego.
Jednak ważne jest, aby rozróżnić te dwa. Różnica polega na tym, jak wzbudzane są elektrony cząsteczek. W chemiluminescencji energia generowana w wyniku reakcji chemicznej wzbudza elektrony, podczas gdy we fluorescencji elektrony są wzbudzane przez bezpośrednią absorpcję energii świetlnej lub innego promieniowania elektromagnetycznego. Gdy elektrony rozluźniają się do stanu podstawowego, oba rodzaje luminescencji uwalniają energię w postaci emitowanego światła.
Rzućmy okiem na przykład każdego z nich. Kiedy świecisz światłem UV na butelkę z tonikiem, elektrony w chininie pochłaniają energię i są wzbudzane do wyższego poziomu energetycznego. Kiedy elektrony się rozluźniają, uwalniają energię w postaci niebieskiego światła.
Zastanówmy się teraz nad świecącą pałeczką, która ma zewnętrzną rurkę zawierającą szczawian difenylu i barwnik oraz wewnętrzną rurkę zawierającą nadtlenek wodoru. Kiedy zginasz świecącą pałeczkę, wewnętrzna rurka pęka, umożliwiając mieszanie się reagentów. Nadtlenek wodoru utlenia szczawian difenylu, tworząc fenol i nadtlenek cykliczny. Cykliczny nadtlenek rozkłada się na dwutlenek węgla, uwalniając energię, która wzbudza barwnik na wyższy poziom energetyczny. Gdy barwnik rozluźnia się do stanu podstawowego, uwalniany jest foton światła. W tym przypadku proces ten jest chemiluminescencją, ponieważ energia dostarczana do wzbudzenia barwnika pochodzi z reakcji chemicznej.
W tym laboratorium zsyntetyzujesz 3-aminoftalhydrazyd, znany również jako luminol, wykonując serię reakcji. Następnie zareagujesz luminol z dimetylosulfotlenkiem na stałym wodorotlenku potasu, aby zaobserwować jego chemiluminescencję.

synteza luminolu

Reakcje chemiczne można sklasyfikować jako endotermiczne lub egzotermiczne w zależności od tego, czy reakcje pochłaniają, czy uwalniają ciepło, gdy zmieniają się w produkty. Różnica energii między reagentami a produktami jest znana jako entalpia reakcji. Oblicza się to, obliczając różnicę energii między produktami a reagentami lub ΔH. Jeśli ΔH jest dodatnie, reakcja jest endotermiczna; Jeśli jest ujemny, reakcja jest egzotermiczna. Podczas gdy reakcje chemiczne są tradycyjnie uważane za konwersję reagentów w produkty, wiele reakcji zachodzi w wielu etapach, tworząc produkty pośrednie. W reakcjach chemiluminescencyjnych te produkty pośrednie przechodzą ze stanu wysokoenergetycznego do stanu podstawowego, uwalniając foton światła, który może być widoczny w miarę postępu reakcji.
<h4>Poziomy energii atomowej</h4>
Niels Bohr, duński fizyk, zaproponował teorię, że elektron krążący wokół jądra atomu może zajmować tylko określone orbity lub poziomy energetyczne. Mówi się, że atom, którego wszystkie elektrony znajdują się na najniższym możliwym poziomie energetycznym, znajduje się w stanie podstawowym. Kiedy elektron zajmuje poziom energii wyższy niż stan podstawowy, atom jest w stanie wzbudzonym.
Kluczowym założeniem teorii Bohra jest to, że elektron pozostaje w stanie podstawowym, dopóki nie zostanie zakłócony. Tak więc elektron jest wznoszony do stanu wzbudzonego tylko poprzez pochłanianie energii. Kiedy elektron rozluźnia się z powrotem do stanu podstawowego, uwalnia tę energię. Często ma to postać fotonu światła, którego długość fali jest bezpośrednio związana z różnicą energii między stanem wzbudzonym a stanem podstawowym.
Kiedy elektron jest wzbudzany do wyższego poziomu energetycznego poprzez pochłanianie światła o określonej energii lub długości fali, zjawisko to nazywa się fluorescencją. Efekt ten można zobaczyć, jeśli wystawisz wypraną białą koszulkę na działanie czarnego światła lub światła UV. Charakterystyczny blask jest spowodowany fluorescencją detergentu i związków wybielających w koszuli, które sprawiają, że wygląda ona na białą w zwykłym świetle.
<h4>Chemiluminescencja</h4>
W reakcji chemiluminescencyjnej elektron jest wzbudzany przez pochłanianie ciepła, które jest uwalniane podczas reakcji. Następnie światło jest uwalniane, gdy elektron rozluźnia się z powrotem do stanu podstawowego. Główna różnica między chemiluminescencją a fluorescencją polega na tym, że energia wzbudzająca elektrony w chemiluminescencji pochodzi bezpośrednio z reakcji.
Jednym z praktycznych zastosowań chemiluminescencji są komercyjne pałeczki świecące. Świecąca pałeczka zawiera dwa oddzielne roztwory: jeden zawiera nadtlenek, a drugi szczawian difenylu i barwnik barwiący. Kiedy te dwa roztwory są mieszane, co następuje po aktywacji świecącej pałeczki, wynikowa reakcja między nadtlenkiem a szczawianem difenylu wytwarza energię, która wzbudza barwnik do wyższego stanu energetycznego. Po wyczerpaniu reagentów barwnik powraca do stanu podstawowego i uwalnia światło. To właśnie sprawia, że świecące pałeczki mają charakterystyczny kolor.
<h4>Luminol (Luminol)</h4>
Luminol to substancja chemiczna, która wykazuje właściwości chemiluminescencyjne i jest wykorzystywana w szerokim zakresie zastosowań, w szczególności w kryminalistyce. Luminol (C, 8, H, 7, N, 3,O2) emituje kolor niebieski po zmieszaniu ze środkiem utleniającym. W przypadku medycyny sądowej luminol reaguje z żelazem zawartym w hemoglobinie, umożliwiając naukowcom medycyny sądowej zidentyfikowanie bardzo małych śladów krwi.
Luminol jest syntetyzowany w reakcji odwadniania kwasu 3-nitroftalowego z hydrazyną. Reakcja jest podgrzewana w celu usunięcia wody i dodawany jest glikol trietylenowy w celu dalszego zwiększenia temperatury. Grupa nitrowa 3-nitroftahydrazydu jest następnie redukowana za pomocą ditionianu sodu w celu utworzenia grupy aminowej o wysokim pH. W podstawowych warunkach 3-nitroftalhydrazyd jest rozpuszczalny. Dodanie lodowatego kwasu octowego powoduje wytrącenie luminolu.
Z wodorotlenkiem potasu luminol tworzy dianion. Aniony wodorotlenkowe deprotonują dwa wodory, które są przyłączone do azotów w luminolu. Gazowy tlen utlenia luminol do stanu wzbudzonego. Gdy relaksuje się z powrotem do stanu podstawowego, uwalnia niebiesko-białe światło.
<h4>Odwołania</h4>
<ol>
	<li style="font-size:17px">Kotz, J.C., Treichel Jr, P.M., Townsend, J.R. (2015). Chemia i reaktywność chemiczna. Belmont, Kalifornia: Brooks/Cole, Cengage Learning.</li>
</ol>

Synteza luminolu

Reakcje chemiczne można sklasyfikować jako endotermiczne lub egzotermiczne w zależności od tego, czy reakcje pochłaniają, czy uwalniają ciepło, gdy zmieniają się w produkty. ...

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JoVE Lab Manual

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Synthesis of Luminol

luminol chemiluminescence in forensics

Luminol chemiluminescence shows how a chemical reaction can produce light and help with blood detection. Chemical reactions may be endothermic or exothermic, depending on whether they absorb or release heat as reactants become products. The enthalpy of a reaction is the energy difference between reactants and products, or ΔH. A positive ΔH means the reaction is endothermic. A negative ΔH means it is exothermic.

Many reactions do not happen in a single step. They can pass through intermediates along the way. In chemiluminescent reactions, these intermediates move from a high-energy state to the ground state and release a photon of light. That light can be seen as the reaction continues.

Atomic energy levels help explain why this glow happens. Niels Bohr proposed that electrons can occupy only certain orbits, or energy levels, around the nucleus. An atom is in the ground state when its electrons are in the lowest possible energy level. When an electron moves to a higher level, the atom is in an excited state. The electron must absorb energy to move up, and it releases that energy when it falls back down. This release is often a photon of light, and the light wavelength depends on the energy gap. When light causes this kind of excitation, the process is called fluorescence, such as the glow seen under a black light on a white T-shirt washed with detergent and bleach compounds.

Chemiluminescence is related to fluorescence, but the energy comes from the chemical reaction itself. In glow sticks, one solution contains peroxide and the other contains diphenyl oxalate and a color dye. When the solutions mix, the reaction produces energy that excites the dye. As the reactants are used up, the dye returns to the ground state and gives off light. This is why glow sticks have their characteristic color.

Luminol is a chemiluminescent chemical with an important forensic use. It emits blue light when mixed with an oxidizing agent. In forensic science, luminol reacts with the iron in hemoglobin, which helps detect very small traces of blood. Luminol is made by dehydrating 3-nitrophthalic acid with hydrazine. The reaction is heated to remove water, and triethylene glycol is added to raise the temperature further. Next, the nitro group in 3-nitrophthalhydrazide is reduced with sodium dithionite to form an amino group at high pH. The compound is soluble in basic conditions, and glacial acetic acid is added to precipitate the luminol. With potassium hydroxide, luminol forms a dianion because hydroxide ions remove the two hydrogens attached to the nitrogens. Oxygen gas then oxidizes luminol to its excited state. When it relaxes back to the ground state, it gives off a blue-white light.

Luminol Chemiluminescence in Forensics

lab techniques

Measuring with Accuracy in the Lab

Measuring with accuracy in the lab starts with careful records, the right tools, and correct reading of data. Scientists use lab notebooks to record how an experiment was done. These notes include the amounts of materials used and each step of the procedure. Without that record, an experiment cannot be repeated in the same way. Balances and glassware are used to measure solids and liquids for experiments. The precision of a measurement depends on the equipment used. Digital balances show the...

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Graphs, Curve Fit, and Standard Deviation

Two-dimensional graphs help students compare an independent variable with a dependent variable in science data. In a chemistry example, temperature is the independent variable and volume is the dependent variable. After data are collected, the relationship between the two measurements must be quantified so it can be evaluated and compared with other relationships. A graph can also show when no relationship exists between the two variables. To make a two-dimensional graph, each data point needs...

stoichiometry, product yield, and limiting reactants

stoichiometry-product-yield-and-limiting-reactants

Balancing Equations and Reactant Limits

Chemical equations show how reactants change into products during a reaction. Stoichiometry is the study of the relative amounts of reactants and products. It is based on the Law of Conservation of Mass, which says matter is neither created nor destroyed. Because atoms are only rearranged, the number and identity of atoms must match on both sides of a reaction. That is why a chemical equation must be balanced. A balanced equation has the same number of atoms for each element in the reactants...

redox reactions

Oxidation States in Redox Reactions

Oxidation states help identify redox reactions. In a redox reaction, oxidation is the loss of one or more electrons, and reduction is the gain of one or more electrons. These reactions are often tracked by changes in oxidation state, also called oxidation number. Each atom in a molecule has an oxidation state. This number shows how oxidized an atom is compared with its free elemental form. It is written as the charge an atom would have if every bond were purely ionic. In that model, bonding...

ideal gas law

Gas Laws Behind the Ideal Gas Equation

The ideal gas equation brings together the main gas laws used in chemistry. Gases have molecules that are far apart, so their behavior is described with four measurable variables: pressure, volume, number of moles, and temperature. The ideal gas law links these variables with the gas constant, R, which equals 8.314 J·K−1 mol−1. Boyle’s law describes the link between pressure and volume. When temperature and the number of moles stay constant, pressure and volume change in opposite directions.

acid and base concentrations

Acids, Bases, and pH in Titration

Acids, bases, and pH explain how acidic or basic a solution is. An Arrhenius acid releases hydrogen ions when it dissolves in water, while an Arrhenius base releases hydroxide ions. These reactions also create conjugate partners: an acid forms a conjugate base after losing hydrogen, and a base forms a conjugate acid after losing hydroxyl. Every acid has a conjugate base, and every base has a conjugate acid. pH measures the amount of hydrogen ions in a solution. The pH scale runs from 0 to 14...

buffers

Buffer pH and the Common Ion Effect

Buffer solutions help keep pH steady when acids or bases are added. In water, an Arrhenius acid (HA) dissociates into hydrogen ions, H+, and a conjugate base, A-. More hydrogen ions make a solution more acidic and lower its pH. An Arrhenius base (BOH) dissociates into a conjugate acid, B+, and hydroxide ions, OH-. Strong acids and strong bases usually change pH a lot because they react completely in water and raise the amount of H+ or OH-. Buffers reduce those pH changes. A buffer usually...

enthalpy of reaction

Reaction Heat, Hess’s Law, and Calorimetry

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solubility

Solubility in Water and Other Solvents

Solubility describes how much of a solute can dissolve in a specific solvent. It is usually reported as solute mass per solvent volume or as solute mass per solvent mass. For example, sodium chloride has a solubility of 36 g per 100 mL of water at room temperature. If solubility is given by solvent mass, that mass must be converted to volume for later calculations. Temperature changes solubility. Sodium carbonate dissolves at about 7 g per 100 mL of water at 0 °C, 22 g per 100 mL at room...

metal flame emission

Flame Test Metal Color Clues

Flame testing uses a metal sample and a flame to identify a substance by its color. Each element gives off a characteristic light emission in the flame, so the color can help distinguish one element from another. This same idea appears in fireworks, where different metal components create different colors. The color comes from energy absorbed by the metallic component. When a species absorbs energy, that energy can go into translation, vibration, rotation, or electron excitement. Electron...

balmer series

Hydrogen Emission Lines

Hydrogen emission lines show how electrons move between fixed energy levels in the Bohr model. Niels Bohr proposed this model for the hydrogen atom in 1913. In this model, an electron can only occupy certain orbits, and it cannot exist between them. These energy states are labeled with the quantum number n. The ground state is n = 1. Higher values, such as n = 2, 3, 4, and so on, are excited states. An electron changes state only by absorbing or emitting energy equal to the difference between...

beer's law

Absorbance Spectra and Beer-Lambert Analysis

Absorbance spectra and the Beer-Lambert Law show how light can be used to study molecules in solution. When light hits a substance, it may be absorbed, transmitted, or reflected. A substance often interacts with a range of wavelengths, and each wavelength can affect the molecules or atoms in a different way. When a molecule absorbs light, that energy can be used for translation, vibration, rotation, or electron excitement. Electron excitement is especially important in spectroscopy because it...

concentration dependence

Reaction Order and Rate Constants

Chemical kinetics describes the speed of a chemical reaction. The rate depends on the reaction mechanism, the complexity of the reaction, and the number of reactants involved. Reactant concentration also affects how fast a reaction happens. The rate law is the experimental relationship that connects these factors to reaction rate. In the rate law, each reactant contributes through a reaction order. The general form is r = k[A]^m[B]^n for aA + bB + ... → cC. Here, r is the reaction rate, k is...

temperature dependence

Reaction Rate, Arrhenius, and Catalysts

Chemical kinetics explains how fast a reaction happens and why that speed changes. The reaction rate is the speed of a chemical reaction. It is defined as the change in concentration of a reactant or product over time. Reaction speed depends on several factors, including the concentration of the reactants and the temperature of the reaction. Each reactant affects the rate in a specific way. That relationship is described by the rate law. The rate law is an equation that connects the...

galvanic cells

Battery Power from Redox Reactions

Electrochemistry studies how chemical change and electrical energy are linked. In this branch of chemistry, electrons move from one species to another. That movement can either produce current or be driven by an applied current. The main reaction in electrochemistry is the oxidation-reduction, or redox, reaction. A redox reaction has two half-reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. These changes also shift the oxidation state of each substance. The...

electrolytic cells

Electroplating with Electrolytic Cells

Electrochemistry links electrical energy with chemical change, and electrolytic cells show how electricity can drive a nonspontaneous reaction. In these reactions, electrons move from one species to another. The key chemistry is a redox reaction, or oxidation-reduction reaction, which happens in two half-reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. The substance that loses electrons is the reducing agent, and the substance that gains electrons is the...

proper lab notebook keeping

Recording a Reproducible Lab Experiment

Accurate lab notebook records are essential in science and organic chemistry labs. Without clear notes, descriptions, quantities, and observations, an experiment cannot be repeated or checked. Good record keeping supports reproducibility, which means other people can follow the same work and get similar results. A laboratory notebook is useful in school labs, research settings, and industry. It can also become a legal record when an idea, process, substance, or technique is patented and...

basic organic chemistry techniques

Organic Lab Glassware and Safe Handling

Organic chemistry labs use specific glassware, careful weighing steps, and controlled heating to keep reactions safe and accurate. Beakers and Erlenmeyer flasks are often used for mixing or holding solvents, but they are not meant for measuring volume unless only an approximate amount is needed. Volumetric glassware is used when a precise volume matters. This group includes graduated cylinders, volumetric pipettes, and volumetric flasks. A graduated cylinder is commonly used in the organic lab...

melting points

How Impurities Change Melting Points

Melting point helps identify an organic compound by showing the temperature where a solid turns into a liquid at 1 atmosphere of pressure. It is a physical property, like solubility, density, color, and electronegativity. Because the exact start of melting is hard to measure, the result is reported as a range. The lower end is when the first drops of liquid appear. The upper end is when the last solid has melted. Scientists compare this range with literature values to help identify a compound. <br...

boiling points

Boiling Point and Vapor Pressure

Boiling point and vapor pressure are key physical properties of a liquid. For a pure compound, the boiling point can help identify the substance. In experiments, the boiling point is usually recorded as a range because exact values are hard to measure and may differ by a few degrees from the literature value. Vapor pressure explains why a liquid boils. In a sealed container, some molecules at the liquid surface gain enough energy to escape into the gas phase. At the same time, some gas...

recrystallization

Purifying Crystals by Solubility

Purifying crystals by solubility is a key organic chemistry technique. Recrystallization uses differences in solubility to separate a desired solid product from starting materials, solvent, and impurities. It is one of the three standard purification methods, along with distillation and extraction. Solubility is the maximum amount of a substance that can dissolve in a fixed volume of solvent at a given temperature. Different solutes dissolve in different solvents, and their behavior can vary...

extraction

Separating Mixtures with Solvent Extraction

Solvent extraction is a common way to separate and isolate a target compound in organic chemistry. In this process, a solute moves from one phase to another so it can be separated from unreacted starting materials or impurities. Extraction is also useful when a product is dissolved in a reaction solvent that is hard to remove by evaporation, such as a solvent with a high boiling point. There are three main types of extraction. In solid-liquid extraction, the solute moves from a solid phase...

simple distillation

Separating Liquids by Boiling Point

Separating liquids by boiling point is the goal of distillation. A miscible mixture contains liquids that mix evenly, and it can be heated so that the more volatile liquid evaporates first. Volatility is a liquid’s tendency to vaporize, and boiling begins when bubbles form in the liquid phase. In a closed container, liquid and vapor can reach equilibrium, which means the rate of vaporization equals the rate of condensation. The pressure from the vapor above the liquid is called vapor pressure.

steam distillation

Steam Distillation and Low-Boiling Separation

Steam distillation is a separation method for temperature-sensitive organic compounds. It works best when the organic compound is immiscible in water, meaning the two liquids do not mix. The method helps remove the organic molecule from a non-volatile contaminant without using the higher temperatures needed for many other separations. In steam distillation, the immiscible mixture is heated until both water and the volatile organic compound distill together. The vapor rises to a condenser,...

thin-layer chromatography

TLC Separation by Polarity

Thin-layer chromatography (TLC) separates compounds in a mixture by polarity. It uses the same basic parts as other chromatography methods: a stationary phase, a mobile phase, and the solute. In TLC, the stationary phase is a thin coating on a plate instead of material packed into a column. The stationary phase in most TLC systems is polar silica gel, a form of silicon dioxide. Its surface has OH groups that can form hydrogen bonds. The sample is first spotted on a pencil start line with a...

column chromatography

Separating Mixtures by Polarity

Column chromatography separates compounds in an organic chemistry lab by using differences in physical properties. It is especially useful for microscale separations when less than 10 grams of material is available for analysis. The method can separate a mixture based on solubility, polarity, hydrophobicity, size, and charge. Any chromatography system has three main parts: the stationary phase, the mobile phase, and the sample mixture. In column chromatography, the stationary phase is usually...

hydrolysis of an ester

Soap Formation from Triglycerides

Triglycerides are lipids made of a glycerol backbone linked to three fatty acids. They are common in vegetable oils and animal fats. Plant lipids are the basis of vegetable oils, while animal lipids are used as lard or general sources of fats. A fatty acid has a long carbon chain, usually between 12 and 20 carbons, with a weak organic acid at one end. Some fatty acids contain double bonds. These are unsaturated fats. The double bond usually gives the chain a bent, cis shape. As a result,...

synthesis of luminol

Luminol chemiluminescence shows how a chemical reaction can produce light and help with blood detection. Chemical reactions may be endothermic or exothermic, depending on whether they absorb or release heat as reactants become products. The enthalpy of a reaction is the energy difference between reactants and products, or ΔH. A positive ΔH means the reaction is endothermic. A negative ΔH means it is exothermic. Many reactions do not happen in a single step. They can pass through intermediates...

esterification

Ester Formation and Everyday Fragrances

Esters are organic compounds with a carbonyl group attached to an oxygen that connects to another alkyl or aryl group. Their general formula is RCOOR'. They are often made by reacting a carboxylic acid with an alcohol in an esterification reaction. In this process, the hydroxyl group of the acid is replaced by an alkyl or aryl group. Many simple esters have familiar fruit and flower smells because their structures are small and less complex. Formic acid and methanol can combine to form methyl...

identification of unknown aldehydes and ketones

identification-of-unknown-aldehydes-and-ketones

Carbonyl Tests for Aldehydes and Ketones

Aldehydes and ketones are carbonyl compounds, which means they contain a C=O functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon. Acetone is the simplest ketone, with two methyl groups. An aldehyde is similar, but it has at least one hydrogen attached to the carbonyl carbon. Formaldehyde is the simplest aldehyde, and acetaldehyde has one hydrogen and one methyl group. The carbonyl carbon in both aldehydes and ketones is electrophilic because the oxygen atom...

uv-vis spectroscopy of dyes

How Dyes Absorb Visible Light

Dyes absorb visible light because their molecular structure lets them interact with specific wavelengths. When light hits a substance, some light is absorbed and the rest is reflected or transmitted. The color we see depends on the wavelength that is reflected. A blue substance reflects blue light, around 430 to 480 nm, and absorbs the complementary orange region, around 590 to 630 nm. Compounds that do not absorb in the visible range appear colorless to the human eye. Light also has energy and...

identifying alcohols

Alcohol Tests for Primary, Secondary, and Tertiary

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chemistry

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Luminol Chemiluminescence in Forensics

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