Home
Industries
Chemical

Chemical Monitoring - UV/VIS and NIR Solutions

Guided Wave’s on-line measurement solutions over the past 20 years are as varied as the diverse range of chemicals encountered in chemical manufacturing. 

Our expertise has traditionally been in on-line, real-time near-infrared (NIR) chemical monitoring, but with the recent introduction of our Model 508 diode array spectrophotometer and our Optical Solutions’ brand ChemView photometers, we now extend our solution base into the UV/VIS.  

Thus, we continue to cover your chemical composition measurements in the NIR, such as water and solvent mixtures, and add UV/VIS capabilities for measurement of chlorine, ppm aromatics and color.

NIR has come to dominate in-situ process analysis over IR for liquids, because: 

• Easy-to-maintain optical paths of 1-50 mm
• Mostly unaffected by optical surface fouling
• Use long lengths of optical fibers to:
  • Install the analyzer in a general purpose area
    
  • Monitor multiple sample points from one analyzer
  • Minimize worker exposure to hazardous chemicals

We bring light to the sample, and therefore, you do not have to bring the sample to the lab.

NIR is rich in spectral information that helps to differentiate among straight-chain, double-bonded and aromatic hydrocarbons. For organic mixtures in the NIR, we can distinguish:

• o-, p- and m-xylenes
• ethylene glycol from diethylene glycol
• cyclohexanol from cyclohexanone
• ethylbenzene from styrene

 

We can analyze the disappearance of isocyanate as it reacts with alcohol to produce polyurethane. Signals from amines are readily differentiated from those of hydrocarbons. NIR is ideal for measuring solvent mixtures, such as those containing a ketone, an alcohol and water. Signals from OH in alcohols or molecular water are strong in the NIR, and can also be differentiated from each other. They are much stronger than the organic signals. As a result, NIR is the preferred method for measuring water at the ppm or percent level. Examples include:  

 

• % water in acids (e.g. acetic, sulfuric, HF) and organics
• > 50 ppm water in most organics
• Caustic in water (even in the presence of carbonate and salt)
• ppm water in alcohols (e.g. methanol)
• Solvent mixtures with both alcohols and water

It is not readily obvious, but NIR is quite powerful in the measurement of gases using long fiber optic sample cells. They are a much lower maintenance alternative to gas chromatographs in many applications over time. Here is an actual installation with a 1 meter gas cell (horizontal near the top of the enclosure) measuring <2% propylene in a gas mixture in the NIR. Some other gas examples are:

• Gas identification in tank cars
• <2% ethylene in ethylene dichloride
• Ethylene oxide in reactor headspace
• Hydrogen cyanide and ammonia

 

UV/VIS applications are again diverse for both clear liquids and gases: 

 

• ppm to ppb aromatics in water or other hydrocarbons
• hypochlorite in bleach
• hydrochlorous acid
• Cl2 gas
• Cl2 and Br2 gases in the presence in phosgene in scrubbers

 

and, for the measurement of color:

 

• APHA (Pt-Co) color during purification and product release
• L*a*b* color
• Yellowness Index
• Gardner Color