Why am I getting negative absorbance values?

All Answers (19) A “negative absorbance” means your reference is absorbing more than your sample. You have a “zero error”. You can correct this by displacing your zero reference.

What does it mean to have negative absorbance?

A negative absorbance means that the the intensity of light passing through the sample is greater than the intensity of light passing through the reference.

Is it possible to have a negative absorbance value?

There cannot be an absolute negative absorbance value; it only indicates that your blank Absorbance reading is for some reason higher than the sample reading.

Why do peaks in infrared spectrum appear inverted?

The inverted peaks observed in the spectra correspond to molecular stretching and bending vibrations that only occur at certain quantized frequencies. When infrared radiation matching these frequencies falls on the molecule, the molecule absorbs energy and becomes excited.

What does negative concentration mean?

What do they mean? A negative concentration value indicates that the sample was analyzed but that the concentration was below the determination limits of the analytical method.

Why is my optical density negative?

If your solution in the blank was more absorbant than the suspending medium you would get a negative value. Optical density is usually done at wavelengths with minimum intereference of pigments ( you are not intereseted in the pigment content, but in the particles).

What occurs when a molecule absorbs infrared radiation?

When molecules absorb IR radiation, transitions occur from a ground vibrational state to an excited vibrational state (Figure 1). For a molecule to be IR active there must be a change in dipole moment as a result of the vibration that occurs when IR radiation is absorbed.

What is the difference between transmittance and absorbance in FTIR?

Actually, FTIR never measures absorption, but transmittance or reflectance. Somewhat naively, it is assumed that what is not transmitted must be absorbed, on this the definition of transmittance absorbance is based (A = -log T). Furthermore, it is compatible with Maxwell’s equations while absorbance is not.

Can you have a negative molar concentration?

It is impossible to have a negative amount of moles. It is also impossible to have a negative mass of solvent.

Can change in concentration be negative?

The concentration of a reactant always decreases with time, so Δ[A] and Δ[A] are both negative. Since negative rates do not make much sense, rates expressed in terms of a reactant concentration are always preceded by a minus sign to make the rate come out positive.

Is absorbance always less than 1?

For most spectrometers and colorimeters, the useful absorbance range is from 0.1 to 1. Absorbance values greater than or equal to 1.0 are too high. If you are getting absorbance values of 1.0 or above, your solution is too concentrated.

How bonding will affect absorption frequency in IR spectroscopy?

The position of an IR-Absorption Band The stronger the bond, the greater the energy required to stretch it. The frequency of the vibration is inversely proportional to the mass of the atoms, so heavier atoms vibrate at lower frequencies.