Peso molecular en instrumentacion

8.35

Molecular Weight
A. BRODGESELL
(1969, 1982)

TO RECEIVER

B. G. LIPTÁK

(1995, 2003)

Mw Flow Sheet Symbol

AT

Applications: Types:

Measurement of the molecular weights of polymers and of other larger molecules A. B. C. D. E. F. G. H. Membrane osmometers Vapor pressure osmometers Light-scattering photometers Viscometers (also see Sections 8.63 and 8.64) Liquidchromatographs, gel-permeation (also see Section 8.13) End group determination Electron microscopy (also see Section 8.47) Ultracentrifuge sedimentation

Design Pressure: Design Temperature: Element Material: Inaccuracy: Range: Costs:

Atmospheric 300°F (150°C) Glass, Kel-F, gel-cellophane, stainless steel 5 to 10% Molecular weight of 50 and higher A, B, C. About $10,000 D. See Sections 8.63 and 8.64.Mooney viscometers, processability testers, and rubber analyzers, from $35,000 to $80,000 E. Over $50,000 G. About $100,000 H. Laboratory centrifuges, from $3000 to $10,000 For liquid chromatographs, see Section 8.13, and for viscometers, see Sections 8.63 and 8.64. Advanced Instruments Inc. (A, B) (www.aitests.com) Alpha Innotech Corp. (www.alphainnotech.com) Ampho Tech Ltd. (www.amphotech.com)Baartlett-Williams Sci., (www.bartlett-williams.com) Beckman (H) (www.astbury.leeds.ac.uk) Beckman Coulter (E) (www.beckman.com) B&H (G) (www.bhphotovideo.com) Bohlin Rheology (D) (www.bohlinusa.com) C.W. Brabender Instruments Inc. (D) (www.cwbrabender.com) Bourevestnik Inc. (A, B) (www.bourevestnic.com) Brookfield Engineering Laboratories Inc. (D) (www.brookfieldengineering.com) BrookhavenInstruments (www.bic.com) BTG Inc. (D) (www.btghome.com) Cambridge Applied Systems Inc. (D) (www.cambridge-applied.com) Cole-Parmer Instrument Co. (www.coleparmer.com) Dennis Kunkel Microscopy (G)(www.denniskunkel.com) Dynatrol Viscosity Systems (D) (www.dynatrolusa.com) Electron Microscope Unit (G) (www.mos.org.sln) FEI Co. (G) (www.feicompany.com) Gynkotek HPLC Inc. (E) (www.gynkotek.com)


PartialList of Suppliers:

1457
© 2003 by Béla Lipták

1458

Analytical Instrumentation

Hewlett Packard (E) (www.hp.com) HPLC Technology Co. (E) (www.hplc.co.uk) Knauer Co.(A, B) (www.knauser.net) Leo Electron Microscopy (G) (www.leo-usa.com) Malvern Instruments (www.malverninstruments.com) Millipore S.A. (www.millipore.com) Nametre Co. (D) (www.nametre.com) Pegasus Scientific Inc.(www.pegasusscientific.com) Perkin-Elmer Corp. (www.instruments.perkinelmer.com) Polymer Laboratories Ltd. (www.polymerlabs.com) Precision Detectors Inc. (www.precisiondetectors.com) Protein Solutions (www.protein-solutions.com) Proteus di Marchi Fabio (G) (www.proteus-lab.com) Regis Technoligies Inc. (E) (www.registech.com) Rohm Haas (E) (www.rhcis.com) Scanning Electron Microscope (G) (www.usyd.edu.au/sv/emu)Siemens Energy & Automation Inc. (E) (www.sea.siemens.com) Solartron Mobrey (D) (www.solartronusa.com) Techne Inc. (D) (www.techneusa.com) Thomson Instrument (E) (www.hplc.com) Varian Inc. (www.varisninc.com) Waters Corp. (E) (www.waters.com) Wyatt Technology Corp. (www.wyatt.com)

INTRODUCTION Molecular weight measurement of gases and vapors has already been discussed in the chapter on densityin Section 6.10 and in several sections of this chapter. Therefore, this section will concentrate only on the measurement of liquid molecular weights. Some of the instruments used in the measurement of the molecular weights of larger molecules, such as viscometers or gel-permeation chromatographs, are treated in more detail in Sections 8.13, 8.29, and 8.64 of this chapter. THE AVERAGE MOLECULARWEIGHT Polymers consist of large molecules formed by the bonding of relatively simple and similar parts. The size and shape of the polymer molecules are determined by the number of basic building blocks and by the way these are linked together. For example, the basic blocks might be arranged in chains of various lengths, in chains with branches, or in two chains linked in several places. Thus,...