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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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How to precipitate Urea in a blood sample?

I am trying to use IR spectroscopy to measure total protein in blood. Urea creates a interference in that range. I thought about precipitating urea to reduce its interference but how can i do that?
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1answer
47 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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128 views

UV-Vis Spectroscopy: How would a negative absorbance reading occur?

My lab is puzzled by strange readings coming out of our Ocean Optics USB4000 Spectrophotometer: After zeroing the instrument with an empty optical glass cuvette, the expected abs(Absorbance)<0.01 ...
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42 views

Beer's law relationship for light scattering at 90 degrees

First-time poster here In Beer's law, the ratio of incident light intensity, $I_0$, to exiting light intensity, $I$, is defined as $\log_{10} (\frac {I_0} {I}) = \epsilon L c$. Then, by rearranging ...
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1answer
32 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
38 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
73 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
51 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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1answer
111 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
159 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
203 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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0answers
38 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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0answers
56 views

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
141 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
104 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
122 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 ...
2
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1answer
24 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
167 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
115 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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0answers
196 views

Propagating Uncertainties for a Dilution to make a Standard Curve [closed]

So I made a standard/calibration curve for $\ce{CuCl2}$ (Absorbance vs Concentration), and to do that I had to start off with an initial concentration of $\ce{CuCl2}$, which was $\pu{0.5 M}$, dilute ...
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0answers
53 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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1answer
567 views

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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0answers
80 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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55 views

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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2answers
2k views

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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32 views

Following conformational isomerization via double resonance spectroscopy

I have some questions about applying double resonance (IR-UV, UV-UV) spectroscopy developed by Zwier's group (J. Phys. Chem. A, 2006, 110, 4133–4150). If we excite the conformer $\ce{A}$ with photons ...
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27 views

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
1k views

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
93 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
205 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 ...
2
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1answer
84 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 ...
4
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1answer
89 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 ...
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1answer
506 views

Why decarbonate soda for spectroscopy experiment?

I did an experiment with a nanodrop photometer where I had to find the amount of caffeine and benzoic acid in soda. During the experiment, we were to decarbonate the soda by heating it. I've done a ...
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641 views

Home science optical absorption test for approximate caffeine quantity in coffee?

I started with How can you measure the caffeine content of a liquid at home? in the cooking stackexchange, but the test strips were only qualitative (yes/no) and don't seem to exist anymore, and the ...
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1answer
124 views

DIY spectrometers limits as a water quality sensor

What pathogens or harmful stuff IN WATER can you detect with these homemade video spectrometers (webcam) + UV light? https://www.youtube.com/watch?v=IA5BTD-aelo I'm trying to do a cheap spectral ...
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2answers
2k views

Absorption coefficient for liquid water

Wikipedia has this plot of the absorption spectrum of liquid water: The vertical axis seems weird to me. The Beer-Lambert Law says $T=10^{Ax}$ where $T$ is the fraction of light transmitted, $A$ is ...
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141 views

Cheap spectral analysis to analyze water quality

I need some guide about spectrometers I saw a lot of DIY spectrometers to analyze light. Does anyone try to use those DIY spectrometers to analyze water? To detect heavy metals? or a chemical? or ...
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2answers
49 views

Is this online fluorophore database reliable?

I need fluorescence spectra for various fluorophores in certain dispersion media for some calculations. There is an online database of University of Arizona: http://www.spectra.arizona.edu/ Is using ...
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284 views

pH versus absorbance

So, as part of a project, comparing theoretical and experimental pH curves for a strong acid and a strong base, I need to measure absorbance and express it in terms of pH. This is because we don't ...
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1answer
214 views

Sample preparation for UV analysis of drug content in capsules/tablets

I want to analyse the drug content of a sample of gelatin capsules filled with active drug (declared dose is known) and excipients such as lactose monohydrate, microcrystalline cellulose etc. with UV ...
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1answer
3k views

Why does the reduction of NAD+ to NADH change the absorbance so much, and cause fluorescence?

This is an updated question: I don't have a very strong background in biophysics, but I want to understand the theory behind NAD and NADH absorbance and fluorescence. Background: I understand that ...
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0answers
53 views

Does the frequency of incident light change in Beer-Lambert Law?

The Beer-Lambert law is meant to describe the interaction between a solute and incident light. But, does the frequency of the light here change due to the interaction with molecules? I think there ...
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2answers
149 views

How to use a spectrometer to determine NPK

I'm trying to determine if it's possible to use a low-grade spectrometer to read NPK values of a solution. I believe I should be able to take readings of the individual compounds (e.g., calcium ...
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0answers
85 views

absorption spectrum of water at different wavelengths [closed]

I know I can get the visible absorption spectrum of water https://en.wikipedia.org/wiki/Water_absorption But how does one go about getting and testing what the absorption spectrum is for a glass of ...
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1answer
441 views

Adding non stoichiometric amount of NH3 to copper solution

Consider the following reaction: $$\ce{Cu(H2O)_n^2+ + 4NH3 -> Cu(NH3)4^2+}$$ The amount of ammonium hydroxide added to your penny solution was not controlled (i.e. you did not add “...
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1answer
433 views

How to determine accurate mass of beta-carotene from beta-carotene extract using spectrophotometer?

In this video, a beta carotene extract(the first yellow fraction) is obtained from $0.5$ g of presumably raw spinach. The extract contains beta-carotene dissolved in organic solvent (9 to 1 hexane to ...
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2answers
455 views

Spectrometry in Chemistry & Flame Test Lab

Question 1: You currently see two colors that are two similar (dark yellow and orange) in a flame test lab. And also you have a hard time differentiating the colors, what is an alternative to ...
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1answer
472 views

Measuring turbidity using a spectrophotometer

I am conducting a lab investigating on the effect of aluminium sulfate concentration on turbidity. In my high-school, we only have a spectrophotometer. Is there a way to measure turbidity with a ...
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1answer
383 views

How to measure concentrations using emission spectrum?

Imagine I am using emission spectroscopy to identify the presence of ions in a solution. Would it be possible to use the intensity of the spectrum to find the concentration of each ion in the ...