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Getting in contact: versatile sampling accessory extends the potential of any FT-IR.

Getting In Contact: Versatile Sampling Accessory Extends the Potential of Any FT-IR

Since its introduction in 1986, the Contact Sampler has proved to be a very flexible infrared sampling accessory. The system's unique design makes it suitable for a wide range of sample types. Many samples can be analyzed without time-consuming sample preparation, thus increasing total sample throughput on the instrument.

The Contact Sampler is a horizontal ATR sampling device that offers users a unique degree of versatility in FT-IR sampling. At the heart of the system is a patented horizontal ATR crystal. The crystals are available with either a flat (for solids or films) or trough (for liquids or semi-solids) sampling surface. The unique crystal mount permits the easy interchange of crystals without the need for realignment of the accessory. A wide variety of crystals which vary in the choice of crystal material and incidence angle, allows the user to customize the effective pathlength and sampling surface according to individual sample requirements. As a result, virtually any material can be analyzed via the Contact Sampler. The applications in this article illustrates the potential of the Contact Sampler for analysis of liquid samples.

Liquids

The trough configuration is well-suited to a wide range of liquid samples, including strongly absorbing materials. The Contact Sample provides:

* a short, reproducible pathlength for excellent

quantitative analyses

* direct, in-situ analyses

* easy sample introduction and cleaning

Example 1: Coffee - Aqueous Liquids

Strongly absorbing samples, such as aqueous solutions, are ideally suited to analysis via the Contact Sampler. The water subtracted spectrum of cold coffee with milk shown at right demonstrates the sensitivity to dissolved components possible with the system. This spectrum, acquired from using a 45 [degrees] Ge trough crystal, clearly shows bands from milk lactose, protein, and caffeine.

Example 2: Engine Oil - Viscous Liquids

The Contact Sampler has gained wide acceptance as a means of assessing engine oil degradation and engine wear. The Contact Sampler provides quick sample introduction and easy cell cleaning even for viscous samples like oils. Engine oil is strongly absorbing, hence a 60 [degrees] ZnSe trough would normally be the crystal of choice. In this example, however, a 45 [degrees] ZnSe cystal has been used to enhance spectral response in the fingerprint region. In particular the degradation was monitored of an anti-wear ingredient, zinc dialkyldithiophosphate, with a strong absorbance at 975 [cm.sup.-1]. As shown, the additive has virtually disappeared in the used oil spectrum versus the new oil spectrum.

In-Situ Monitoring

The sensitivity of FT-IR in conjunction with sampling flexibility of the Contact Sample produce a perfect team for in-situ monitoring applications. An array of sampling crystals assures an appropriate combination of crystal durability and infrared sensitivity to achieve an optimized analysis.

Example 3: Drying of an Alkyd Resin

The effects of film thickness on the drying of all alkyd resin based paints can be directly monitored by ratioing the intensity of the carbonyl bank at [1735cm.sup.-1]. To avoid saturation of the strong carbonyl band, a 60 [degrees] ZnSe crystal was used. The cured resin was readily cleaned from the trough with either methylene chloride or acetone. The unique out-of-compartment design permits convenient use of UV lamps or other radiation sources to evaluate their effects on rate or cure.

Quantitative Analysis

The design of the Contact Sampler ensures a consistently, reproducible pathlength for convenient quantitative analyses.

Example 4: Toothpaste

Multicomponent analyses in a production environment are among the most demanding applications for an FT-IR sampling system. The environment demands sturdy instrument and accessory design, ease of operation for nonspecialized staff, and speed of analysis. Monitoring quality during toothpaste manufacturing is an example of this application. The analysis was carried out using a 60 [degrees] ZnSe trough crystal at [4cm.sup.-1] resolution using a dTGS detector. The 60 [degrees] crystal was chosen to avoid saturation of the strong absorbance around [1000cm.sup.-1] due to abrasive.

A series of 10 standards was manufactured to bracket acceptable control limits. At least squares curve fitting routine over the 1870-[880cm.sup.-1] region was used to establish a calibration curve. Standard concentrations were verified by wet chemical and gas chromatographic methods.

Production samples of unknown composition were analyzed by squeezing directly into the trough - covering the whole crystal surface. The table under the graph shows the result for three major ingredients on three different toothpaste samples. As seen, FT-IR offers a time saving alternative to traditional methods for QC analyses of pastes like toothpaste.

PHOTO : Figure 1 Aqueous Liquids

PHOTO : Figure 2 Viscous Liquids

PHOTO : Figure 3 Alkyd Resin Drying

PHOTO : Figure 4 Multicomponent Analysis

PHOTO : The Contact Sample from Spectra-Tech is suitable for a number of applications and a number of sample types.
COPYRIGHT 1991 Chemical Institute of Canada
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Fourier transform infrared spectroscopy; Spectra-Tech Inc.'s Contact Sampler
Author:Wasacz, Frank
Publication:Canadian Chemical News
Date:Jan 1, 1991
Words:785
Previous Article:National Chemistry Week in Edmonton.
Next Article:Applied Research Centre for Polymers.
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