Instrumental Technique: Cuvette. Md Rabiul Islam

Transcription

1 Instrumental Technique: Cuvette Md Rabiul Islam

2 What is cuvette? A cuvette is a small tube of circular or square cross section, sealed at one end, made of plastic, glass, or fused quartz (for UV light) and designed to hold samples for spectroscopic experiments. Cuvette is used in different instruments such as Spectrometers, Spectrophotometers and Fluorometers etc. Cells and cuvettes for UV/VIS and fluorescence spectroscopy are available in a large variety of materials, from low-priced disposable plastic cuvettes to highperformance quartz cells. The best cuvettes are as clear as possible, without impurities that might affect a spectroscopic reading. Cuvettes are commercially available in path lengths of 0.1 to 10 cm.

3 In general cuvettes are used into three groups(on the basis of materials used in it ) 1. Glass cuvette ( Silicate glass ) 2. Plastic cuvette and 3. Quartz cuvette Glass, with a wavelength from 380 to 780 nm (visible spectrum) Plastic, with a wavelength from 380 to 780 nm (visible spectrum) Quartz, with a wavelength below 380 nm (ultraviolet spectrum) Quartz consists exclusively of silicon dioxide (SiO 2 ) and shows some remarkable properties: Quartz displays a high UV transmission, in highly purified synthetic quartz down to well below 200 nm. In certain applications such as an extremely dilute sample where the utmost in sensitivity is essential quartz may be the only option. The thermal expansion of quartz is extremely low, its coefficient of thermal expansion being 6 x 10-7 K -1 between 20 C and 300 C. Quartz is chemically very resistant and maintains its shape, even at high temperatures up to approximately 1000 C.

4 Common criteria for all types of optical glass are: It is used in the visible range of the spectrum. It display good resistance to chemicals. Plastic cuvette/disposable Cuvettes ( visible region and transmit light from nm ) Disposable plastic cuvettes are often used in fast spectroscopic assays, where speed is more important than high accuracy. It is made by PS (Polystyrene) and PMMA (Poly(methyl methacrylate)) and PC (polycarbonates are clear and fairly resistance to UV light) Plastic cuvettes are used in the visible range for colormetric assays and the UV range for DNA, RNA, and protein analysis. Semi-micro size cuvettes are for sample volumes between 1.5mL and 3.0mL, macro cuvettes for samples larger than 2.5mL. and ultra-micro sized cuvettes may be used with sample volumes as small as 70µL.

5 Advantage of plastic cuvette: Disposable cuvettes have many advantages over quartz. Since quartz cuvettes are so expensive, typically costing hundreds of dollars, UV-Cuvettes costing much less than a dollar each are economical. They eliminate the risk of sample carryover, so they can enhance the reliability of analytical results. They eliminate time-wasting washing of cuvettes; taking 5 minutes to wash and dry a cuvette costs more than the price of a UV-Cuvette. They eliminate the sample carry-over risk of reusable cuvettes, and the risk of scratching or breaking expensive quartz. In molecular biology applications, the availability of individually wrapped UV- Cuvettes (BRAND UV-Cuvette), free of DNA, DNase and RNase, provides superior protection for your samples that is not available with reusable quartz cuvettes.

6 Proper selection, use, and care of cuvettes: 1. Cuvettes are made from plastic, glass, or quartz. a. Use quartz cuvettes for UV work. b. Glass, plastic or quartz are acceptable in visible work. c. Generally plastic cuvettes strongly absorb UV, which is why they cannot be used in spectroscopy in the UV range but there are inexpensive plastic cuvettes (BRAND UV-Cuvettes, it is Ideal for DNA, RNA, and protein analysis and transparency from 220 to 900nm) that may be suitable for some UV work. 2. Cuvettes are expensive and fragile (except for disposable plastic ones). Use them properly and carefully. a. Do not scratch cuvettes; do not store them in wire racks or clean with brushes or abrasives. b. Do not allow samples to sit in a cuvette for a long period of time. c. Wash cuvettes immediately after use. d. For fluorometers cuvettes must be optically clear on all four sides. e. One must make sure the solvent won t dissolve the cuvette( specially for plastic cuvette).

7