UVI-VIS Spectrophotometer

Question 1

UV-Visible (UV-Vis) spectrophotometers

Answer 1

illuminate samples with light across the UV to visible wavelength range (typically 190 to 900 nm).

Question 2

what wavelength ranges can some spectrophotometers extend to?

Answer 2

into the near-infrared (NIR) (800 to
3200 nm)

Question 3

how does it determine the chemical and physical properties of a sample?

Answer 3

Measurements include the light absorbed, transmitted, or reflected by the sample

Question 4

Applications for UV-VIS spectro

Answer 4

it includes identifying molecules, determining concentrations, characterizing absorbance or transmittance, measuring surface reflectance, and studying chemical or biological reactions.

Question 5

list all the components of the spectrophotometer

Answer 5

1. light source
2. dispersion device
3. sample holder
4. detectors that measure reflected or transmitted radiation
5. Optical components such as lenses, mirrors or fiber optics

Question 6

Light Sources Used in UV-Vis Spectrophotometers

Answer 6

1. deuterium arc lamp
2. Tungsten-halogen lamp
3. xenon-flash lamp

Question 7

Produces good intensity in the UV region (185 to 400 nm) but has a short half-life of about 1,000 hours

Answer 7

Deuterium arc lamp:

Question 8

Provides good intensity across the visible range (350 nm to 3000 nm) and has a longer functional life of approximately 10,000 hours.

Answer 8

Tungsten-halogen lamp

Question 9

Emits brief, high-intensity light (185 – 2500 nm) during measurement, allowing for minimal photobleaching and has a long lifespan, reducing the need for frequent replacements.

Answer 9

Xenon flash lamp

Question 10

narrows broad-spectrum light to selected wavelengths through an entrance slit, a dispersion device, and an exit slit.

Answer 10

monochromator

Question 11

single monochromator

Answer 11

used for general purpose spectroscopy and can be integrated into a compact optical system.

Question 12

This cannot select narrow wavelengths of light

Answer 12

single monochromator wavelengths

Question 13

explain what is a double monochromator

Answer 13

there are two monochromators arranged in a series. the source light is split by the first monochromator and the second further split the light. Spectral accuracy is increased because stray lights are reduced

Question 14

these are used to achieve wavelength separation, which reflect light at different angles depending on the wavelength.

Answer 14

holographic gratings

Question 15

a device to spread the light into
different wavelengths (like a rainbow) and allow
the selection of a nominated band of wavelengths

Answer 15

dispersion device

Question 16

are used to isolate the desired reflection order due to the overlapping nature of the light reflected.

Answer 16

Filters

Question 17

designed to minimize stray light and is typically opaque.

Answer 17

The sample compartment

Question 18

usually made from glass or quartz for effective UV transmission, and hold liquid samples

Answer 18

cuvettes

Question 19

this is where the sample is positioned to allow the beam from the monochromator to pass through the sample.

Answer 19

sample compartment

Question 20

once sample is obtained, how is the absorbance measured?

Answer 20

liquid samples are held in a cuvette with a known and fixed waveleght.

Question 21

what materials are cuvettes made of?

Answer 21

glass, quartz, or plastic

Question 22

Standard cuvettes have a ____ pathlength and are
made from quartz, to ensure good transmittance of UV
wavelengths

Answer 22

10 mm

Question 23

common types of cuvettes and their suitable wavelength

Answer 23

1. optical glass cuvettes : 340 - 2500 nm (visible spectrum)
2. ES quartz Cuvette :190 - 2500 nm
3. IR quartz cuvette: 2500 - 3500 nm
4. polystyrene PS or polymethyl methacrylate (PMMA): 380 - 780 nm

Question 24

spectrophotometers that measure one sample and require separate blank measurements, which can lead to inaccuracies.

Answer 24

Single beam spectrophotometers

Question 25

it can simultaneously measure reference and sample beams, allowing for real-time optical performance adjustment and increased measurement accuracy.

Answer 25

Double beam spectrophotometers

Question 26

what converts the light from the sample into an
electrical signal?

Answer 26

the detector

Question 27

what are the two types of detecting systems that are sensitive to certain wavelength ranges?

Answer 27

photomultiplier tube detector and
photodiode detector

Question 28

why is important to clean and handle cuvettes properly?

Answer 28

Fingerprints can significantly impact results; optical surfaces should be kept clean to avoid erroneous measurements.

Question 29

how do you maintain the cuvettes?

Answer 29

immediate sample removal to prevent sticking, proper storage (either dry or in a suitable acid just not HF), and ensuring thorough cleaning using appropriate methods. Strong acids and basic solutions should be avoided, as they can degrade the optical surfaces over time