AOTF Technology & Applications

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INTRODUCTION – NEAR INFRARED PRINCIPLE

The near-infrared (NIR) region can be defined as the wavelength region from 700 to 2500 nm. It was discovered that different chemical bonds (like O-H, C-H, and N-H) vary in strength and energy with respect to their vibrations and can be seen in the spectrum as a series of absorptions at different wavelengths. Identifying these “peaks” at particular wavelengths provides the opportunity to measure the amount of a particular molecule that is present in the sample.

However, interpreting NIR spectra can be very difficult without the use of data processing and chemometric software. There are typically four phases of analysis:

1. Data collection – sample spectra and measurements are taken with a chosen spectrometer and method (i.e. transmission, reflectance, transreflectance)

2. Data processing – includes signal processing to prepare the sample for chemometrics

3. Calibration – chemometrics, which uses a variety of methods to build a “model” used for analysis

4. Prediction – use of the chemometrics model to accurately predict an unknown sample

BRIMROSE AOTF-NIR

There are a variety of NIR techniques including Fourier Transform (FT), Monochromator, Polychromator (Diode Array), and Filter. FT uses a moving mirror and is, therefore, sensitive to vibrations. Monochromators, using diffraction gratings, require careful handling and frequent calibration. Diode Array has lower resolution and signal-to-noise ratio than other techniques. Filter has a very limited wavelength range and can only be used for single component measurement such as moisture.

The Brimrose Acousto-Optic Tunable Filter (AOTF) technology is well suited to most applications in the laboratory, at-line, and especially in-line.

The following are advantages over other NIR techniques:

• Solid State – no moving parts, therefore it is immune to ambient vibration

• Faster – up to 10 measurements / second and capable to scan up to 16,000 wavelengths per second, therefore can get up to 30 scans per second across the whole wavelength range (1100-2300 nm)

• Customized for Purpose (ATEX / UL / IPxx)

• Sensitive – higher resolution with excellent signal-to-noise ratio

• Immune to Ambient Light – no need to block ambient light from the sample

• Real-Time Dual Beam Reference – no drifting, excellent wavelength repeatability, no need to recalibrate the device

The Brimrose AOTF-NIR spectrometers use a Telerium-Dioxide (TeO2) crystal in combination with an RF generator. A white light source (Tungsten) is supplied to the crystal. The RF generates acoustic waves that propagate through the crystal and allow the crystal to diffract one wavelength of light. Changing the frequency of the RF easily and quickly allows different wavelengths to pass very rapidly. The individual wavelengths are then split into 2 beams of light. The “reference” channel includes 5% of the light and is diverted to a polystyrene reference detector. The remainder of the light is the “sample” channel and passes to the sample and returns to an InGaAs detector. The reflected (or transmitted) light from the sample is divided by the reference to create a true spectrum for analysis that doesn’t require operator interaction.

Unlike other spectrometers, the AOTF-NIR spectrometers designed and built by Brimrose are rugged, flexible, and simple to operate.

AOTF-NIR APPLICATIONS

NIR spectroscopy is a technique that has gained widespread acceptance as a powerful diagnostic tool, particularly for quality assurance and process analytical control (PAT) purposes in pharmaceutical, food/agricultural, and chemical industries. NIR has been in use in the pharmaceutical industry even before PAT initiative was introduced in the early 2000’s. The initial use for NIR was for raw material identification to reduce the costs and time of laboratory testing.

Since its early adoption in the mid 1980’s for raw material identification, NIR use has expanded for in-line and at-line testing:

• Measurement of excipients and API’s

• Blending uniformity

• Lyophilization

• Moisture measurement in fluid bed dryers

• Reaction monitoring

• Polymorph determination

• Tablet testing (content uniformity, active concentration, & coating)

• Particle size measurement

Typical food and agricultural applications include measurements of moisture, proteins, fats, and ash. Using NIR not only improves the consistency and quality of manufactured products. It can also be used to:

• Help determine when to harvest

• Identify seeds for breeding

• Indicate counterfeit products

• Improve soil management and fertilization practices

The chemical industry uses NIR to improve its in-line and at-line analysis including:

• Reaction monitoring - polymerization

• Process monitoring to understand the material composition

• Identifying additives and impurities

• Identification of cloud point corresponding to temperature

... and many others. For more applications, contact us directly.