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Questions tagged [spectrophotometry]

A method to measure how much a chemical substance absorbs light by measuring the intensity of light as a beam of light passes through sample solution.

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27 views

Calibration curves and dilution factors

I am currently taking a course where we are exploring nitrate concentrations in water samples. We are using a UV-Vis Spectrophotometer and have created a calibration curve in the first part of the ...
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Preparation of standard Fe from FeSO4 • 7H2O

We were assigned to prepare a standard Fe for spectrophotometry determination of Fe. What we did is basically obtain a mass of FeSO4•7H2O, add a small a mount of distilled water before adding 18M of ...
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If Beer's Law appears to apply to a high concentration (>0.01M) of a solute, is it valid to use for concentration calculation?

Internet consensus seems to define "high concentration" for Beer's Law as >0.01M. If one has a solution at higher concentrations than that, but the absorbance vs. concentration is still linear, is it ...
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61 views

Absorption of UV Light and what color would be seen?

I am mathematically experimenting with different wavelengths of light that a fictional material would absorb. I thought of a material that absorbs a wavelength of $\pu{193 nm}$. This wavelength ...
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Do I have to take the sample buffer into account when determining the protein concentration?

I am measuring the absorbance of a protein that is dissolved in a certain buffer. I know the extinction coefficient for this protein in this buffer. In order to be in the good absorbance range I have ...
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23 views

Soluble compounds to absorb radio-frequency electromagnetic radiation

Are there any soluble compounds capable of absorbing radio-frequency or long microwave radio-frequency electromagnetic radiation? I have noted that metals are often used to absorb these signals, but ...
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32 views

Measure low DOM absorbance values in a microplate reader. Is there a suitable deep well microplate with flat bottoms available?

I would like to use a microplate reader to measure the absorbance of dissolved organic matter (DOM), but the measured values are close to the lower detection limit. To overcome this, I thought of deep ...
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1answer
65 views

Molar absorption coefficient for potassium hydrogen phthalate

I would like to draw a comparison of the sensitivity between several spectrometers. Therefor I measure the absorption of a serial dilution of potassium hydrogen phthalate (KHP). The idea is to compare ...
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25 views

Determination of pKa and molar absorptivity coefficient using spectrophotometry [closed]

An indicator BPB (Brophenol Blue) is used and dissolved in solutions of various known $\mathrm{pH}$. Then, the absorbance of each solution at 590 nm was measured and the question asks for molar ...
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2answers
124 views

Determining Kc for the equilibrium involving iron thiocyanate using spectrophotometric data

$$\ce{Fe^3+(aq) + SCN-(aq) <=> [Fe(SCN)]^2+(aq)}$$ $\pu{12.0 mL}$ of $\pu{0.00110 mol L-1}$ $\ce{Fe^3+}$ was added to $\pu{6.00 mL}$ of $\pu{0.00140 mol L-1}$ $\ce{SCN-}$. The absorbance of ...
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223 views

Does a calibration curve of absorbance vs concentration need to pass exactly through the origin?

If you are making a calibration curve for $\ce{CuSO4}$ where you plot absorbance against concentration and the curve deviates slightly from the origin, does it make the calibration curve useless?
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What is the molar extinction coefficient of azorubine (carmoisine, E 122)

I'd be grateful for the molar extinction coefficient ε of azorubine at the absorption maximum (about 520 nm), with an authoritative reference.
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Choosing the right wavelength for calibration curve and for analysis of actual results

Introduction: I am currently conducting a series of experiments in which I am studying the transport of polystyrene nanoparticles (PNPs) through sand and soil. This is done in sand/soil columns, into ...
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35 views

How to measure UV index? [closed]

I am a high school student so please apologise if I say something very dumb or irrelevant. I am conducting an experiment in which I want to find UV index at different points. Such as under shade, ...
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201 views

When making a calibration curve, do we have to use the wavelength at maximum absorbance?

If you are making a calibration curve for $\ce{CuSO4}$ where you plot absorbance against concentration, does the wavelength have to be exactly at the maximum of the peak? Or can it be somewhere else ...
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1answer
26 views

Can I have a homogeneous 2 molal solution of copper(II) sulfate at 20 °C?

I'm doing a high school chem project where I am making a calibration curve of copper(II) sulfate for spectrophotometry in which I make solutions with five different concentrations. The most ...
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1answer
181 views

Is Beer-Lambert law also valid for fluorescence and luminescence?

When I measure optical density in a microplate reader the absorbance is proportional to the concentration and the height of the liquid. Is Beer-Lambert law also valid for fluorescence and luminescence?...
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23 views

How to find concentration of three species from given molar absorptivities [closed]

If I am given the molar absorptivities of three species at a given wavelength, and I only have the concentration of one of those species, how can I determine the concentrations of each of the ...
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1answer
72 views

Why do you use acetic acid instead of water to create your standard riboflavin solutions?

I must create my own lab and I was going to use water, however, a similar experiment online says that acetic acid should be used to create my standard riboflavin (vitamin B2) solutions. Why is that?
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1answer
55 views

Homemade spectrophotometer to exemplify Beer-Lamberts law

I have built a 12-band spectrophotometer, and i'm currently keen on proving Beer-Lamberts law through a small practical example. The solution that I'm going to test with my spectrophotometer, is ...
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46 views

How does mesh size of Barium Chloride affect sulfate results via turbidimetric method?

I am analyzing sulfate using Standard Methods 4500 $\ce{SO4 ^2-}$ E (turbidimetric method) using $\ce{BaCl2}$ and measuring %T at 420 nm. In the past, we used an appropriate 20-30 mesh size for the $\...
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1answer
77 views

Effective attenuation coefficient for polychromatic light

The Beer-Lambert law gives the optical intensity of collimated light as a function of depth $z$ as: $$I(z)=I_{0}\mathrm e^{-\gamma z},$$ where $\gamma = \alpha + \beta$ is the wavelength-dependent ...
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41 views

How to meausre ion interferences in solution?

Is there a way to quantitatively measure the interference of different metal ions in solution? I plan to measure concentration of Pb(II), Fe(II), and Cu(II) in solution together using a ...
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1answer
78 views

How to interpret detection limits

I am learning about different analytical methods such as Atomic Absorption Spectrscopy and Atomic Emission Spectroscopy and I'm having a difficult time understand how to interpret the detection limits ...
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1answer
85 views

Detection limits

I am given this question: A study showed that over 2000 children in China have been poisoned by lead. Blood samples have been taken and show that there is 10 times as much as the acceptable amount of ...
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1answer
72 views

I'm trying to make an optical dissolved oxygen sensor. I need help finding an appropriate oxygen sensitive dye

I have been trying to make a dissolved oxygen sensor, the basics are described on this page. I have a good understanding of the electronics behind this measurement, but I cannot find a suitable ...
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180 views

Are there any (simple) molecules with very different absorption and emission dipole directions?

When a single molecule absorbs or emits light, it does so perpendicular to the direction of the respective transition dipole. In principle, the directions of the dipoles for absorption and emission ...
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1answer
419 views

Using Nanodrop for UV/Vis analysis of compounds at limited amounts [closed]

I am no chemist, but a biologist who knows some biochemistry. I have some natural extracts at limited quantity, which I have been evaluating using mainly GC-MS. These extracts are rich in liquid ...
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1answer
490 views

Determination of pKa by absorbance and pH of buffer solutions

I've been tasked (as part of a report) to calculate the $\mathrm pK_\mathrm a$ of 4-nitrophenol by measuring the pH and absorbance of six 'buffer solutions' containing the 4-nitrophenol: $$\begin{...
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83 views

UV-Vis and Polylactid Acid (PLA) [closed]

I am trying to use UV-VIS for a 3D printed ~4mm PLA design. However I keep running into a problem because the polymer is not showing detectable under the UV-VIS. Does anyone have any suggestions that ...
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Theoretical limits of (NIR) spectroscopy for quantitative analysis

Edit (months later): In hindsight, I was asking about the theoretical limits of multivariate curve resolution (see Lawton & Sylvestre: Self-modeling curve resolution) in chemometric applications. ...
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1answer
265 views

USNCO Question - Determining solute using spectrophotometer

Below is a question from the 2017 USNCO: The concentration of which approximately 0.01M solution could be most accurately determined by a visible spectrophotometer (or colorimeter)? (A) $\ce{Mn(NO3)...
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1answer
217 views

Absorption spectrum of Hydrogen molecule in UV region 200 nm - 300 nm (not Atomic Hydrogen)

Can somebody provide Absorption spectrum of Hydrogen molecule? I have searched days for absorption spectrum of Hydrogen molecule in 200 nm - 300 nm UV region and All I got is absorption spectrum of ...
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1answer
360 views

Molar absorption coefficient of H2SO4(aq) for UV-vis spectrophotometry

I am wondering if there is anything in the literature that can tell me what is the molar absorptivity (i.e. molar extinction coefficient) of aqueous sulfuric acid at a given wavelength (in my case, I ...
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1answer
30 views

Interference and absortion filters

I am learning a bit about Uv-vis spectroscopy filters. As far as I know there are two commonly used: interference and absotion filters. The first one works with the interference of light principle and ...
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1answer
188 views

What is the range of photon energies can be effectively used to split a diatomic molecule like hydrogen?

I saw photo-ignition of hydrogen-chlorine mixture using UV light on YouTube. Chlorine molecule bond dissociation energy is $\pu{2.51 eV}$ (bluish colour). Bromine molecule bond dissociation energy is ...
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1answer
222 views

Is a spectrophotometric method of measuring the rate of a complex reaction valid?

A few months back I designed and carried out an experiment to measure the rate of the reaction between ferric chloride and copper.The dependent variable was the rate of the reaction; the independent ...
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76 views

How to prepare a water sample for photometry

The purpose of measuring N P K Ca Mg S is to determine the amount of material consumed by different types of plants in different periods. The initial solution, which is prepared as a nutritious ...
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Why does sunlight cause plastics to become a faded blue color?

Due to the UV absorption, I knew that the plastics can be easily affected, especially PP. But is it normal that the change is always into faded blue from white color? and Why? Because I made an ...
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114 views

Blue shift in UV-Vis of ZnO?

The characteristic wavelength of ZnO is supposed to be ~380 nm. However, in this article1, the peak has been blue-shifted to 214 nm. This is quite similar to my sample where the peak is at 200 nm. In ...
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Should I add more of a trihydrate chemical to a solution if recipe calls for hemihydrate?

I am running phosphate by the ascorbic acid method (SM 4500-PE, PDF), and making the antimony potassium tartrate reagent. Standard methods uses $\pu{1.3715 g}$ of $\ce{K(SbO)C4H4O6 * 1/2 H2O}$ per $\...
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Why does tryptophan absorb UV light?

Why is that tyrosine, phenyalanine, and tryptophan absorb UV light while other amino acids don't even absorb visible light? Does it have something to do with aromatocity?
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Why photons with longer wave length demonstrate more active scatter and transmit that shorter length?

Why photons with longer wave length demonstrate more active scatter and transmit that shorter length? This troubles me to understand why NIR and Infra-Red goes through diffused media when compared to ...
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2answers
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Why is absorbance the negative logarithm of transmittance?

What is the physical significance of absorbance? Is it not possible to directly decipher the amount of radiant energy absorbed by the sample from transmittance? Why is that negative log of ...
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1answer
219 views

Why does a smaller bandgap correlate to increased absorption of visible light?

I am currently involved in a project on metal organic frameworks in my AP chemistry class, and specifically their applications in $\ce{CO2}$ reduction into formate. All the explanations we can find on ...
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1answer
308 views

Analysis of methylphenidate (Ritalin) HCl extended release tablets

For a project I have to determine the drug concentration release profile of self-made methylphenidate HCl (MHCl) extended release tablets (hydrophilic matrix). We are thus doing a dissolution test as ...
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1answer
86 views

Compare concentrations using LC/MS

Suppose I run a reaction and then pass the results through LC/MS to find the conversion. One idea could be to compare the peaks of the reactants to the peak of the product. But: MS peak will depend ...
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1answer
3k views

Molar Absorptivity of Copper(II) Sulfate

What is the molar absorptivity of copper sulfate? I am trying to find the molarity of copper sulfate solution by absorption in a spectrophotometer with a cuvette. However, I can't find $\varepsilon$, ...
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119 views

Changes in UV-Vis spectra in host-guest complexes

I'm doing some background reading before conducting an experiment, but am getting a little confused. What serves as evidence for the formation of a host-guest complex when conducting analysis through ...