INLINE Optical Platforms for UV Absorbance Measurement

In practical industrial language, yes — a UV absorbance analyzer and a UV photometer are essentially the same class of instrument. Both measures how much ultraviolet light is absorbed by a process stream, and both output absorbance/transmission values used for concentration and/or purity-related decisions.
These instruments also go by several other names, depending on the industry, marketing spin, or measurement approach:

• UV monitor
• UV process analyzer
• UV process photometer
• Inline UV spectrophotometer (usually when multiple wavelengths are measured)
• UV absorbance sensor
• UV transmission monitor

The terms often overlap. The main differences come down to how many wavelengths they measure, how the optics are built, and whether they’re marketed as single-parameter photometers or multi-wavelength spectrophotometers. But in everyday plant use, they all fall into the broader bucket of UV optical process analyzers.

The difference comes down to how much spectral information the instrument measures and how flexible the optics are.

A UV absorbance photometer (like the Kemtrak DCP007-UV) is usually a single or dual-wavelength device. It passes UV light through the process and measures how much is absorbed at one or two fixed wavelengths. It’s built for process control, not lab-style analysis. The goal is stability, simplicity, and repeatable readings tied to known process parameters — concentration, purity, breakthrough detection, color intensity, and so on. You choose the wavelength(s) up front, and the instrument measures absorbance at only those wavelengths.

A UV spectrophotometer (such as the Kemtrak UV SPECTRA), on the other hand, captures a broader portion of the spectrum. Instead of fixed optics, it uses an array, grating, or other dispersive element to measure a continuous spectral profile. That allows more detailed identification of compounds, multi-component analysis, and deeper diagnostic work. In industry, inline “spectrophotometers” may or may not measure a full spectrum like a lab unit, but they still gather many wavelengths at once, giving more analytical flexibility than a simple photometer.

In short:

Photometer: narrow, fixed wavelength(s); built for specific inline control.

Spectrophotometer: broad, multi-wavelength measurement; built for deeper analysis or multi-component monitoring.

In-line UV photometers (also known as UV monitors, analyzers, and detectors) use light to provide real-time measurement of the concentration of components in a liquid (or gas) process stream. Absorbance photometers can be configured for a variety of purposes, with the configuration and technique used depending upon the specific measurements needed. Simply put, an industrial UV photometer is used to measure the amount of light left (or more specifically, the amount of light lost) in a light beam (often at a specific wavelength) after it has passed through an industrial process stream.

Analytical photometry has been around for many decades. Many earlier photometers were offline units based upon visual standards. They utilized glass plates of specific colors that were compared stereoscopically to process fluid samples with the naked eye. As technology progressed, in-line absorbance instruments using photodetectors were developed that measured light more accurately, repeatably and in real time.

The most common type of photometers, of which the Kemtrak DCP007 is a notable example, uses light absorbance techniques to determine and report the concentration of a particular component in a fluid stream. They are usually configured to operate with one or two discrete wavelengths in the UV-VIS light region depending upon the application. Beer-Lambert law—which relates the reduction in intensity of light as it passes through a material to the concentration of the material absorbing the light—applies in this application. The optical path length must be configured to suit the expected absorbance measurement range.

UV Photometers are typically limited to having a maximum of two wavelengths that can be measured. Using an online spectrophotometer (such as the Kemtrak UV SPECTRA) changes that dynamic and allows for additional wavelengths to simultaneously monitored.

Having more absorbance values available at different wavelengths allows for detailed identification of compounds, multi-component analysis, and deeper diagnostic work. The UV SPECTRA, for instance, scans all wavelengths from 190nm to 440nm and allows users to select up to 10 wavelengths from that scanned range for monitoring purposes.

UV photometers typically measure the concentration of a specific substance or species within a flowing liquid (or gas) stream. Each photometer consists of an advanced electronic unit, with a light bench constructed using high-performance light source technology, rugged industrialized fiber optic cables, and a measurement cell.

Photometers can be found in many industries, but are commonly found in the biotech sector where they are used for chromatographic separation of proteins and filtration performance and breakthrough applications.

Getting the most out of your inline absorbance instrumentation is not as difficult as you might think. If you follow several straightforward steps, you should have no issues with your measurement(s) and get good performance when they are in operation.

• Installation. Wherever possible, always install a photometer in a pipe where flow is vertically upwards. This will ensure the most homogeneous sample is passing through the photometer light beam.
• Flow conditioning. Aeration is the number one interfering factor in online optical measurement performance. In absorbance systems, it makes measurement noisy and creates errors. Suppressing aeration in the flow stream greatly improves the quality of the measurement.
• Fouling compensation. Optical instruments use windows to introduce and extract light from pipelines. In some applications, these windows can become contaminated with process material forming a film or layer on their surfaces, and this looks like absorbance to the instrument because it partially blocks light. By referencing your absorbance measurement at the wavelength(s) of interest against another wavelength where your process doesn’t absorb, you can electronically adjust for window contamination so the measurement remains stable.
• Instrument light decay. Today, LEDs are widely available and older style mercury vapor gas discharge lamp photometers are essentially obsolete. Whatever the light source in your unit, make sure it has the ability to self-check and adjust the light output so that it remains constant. Changing light intensity looks like a change in measurement to a photometer and contributes greatly to drift.
• Stray light. Incidental light getting into your instrument’s optical circuit can create havoc with the measurement. This is not usually a problem with metal pipe installations, but can be quite extreme when installing photometers in plastic pipes and clear tubing as ambient light can travel through non-black materials and enter the light circuit. If you observe trends like measurements declining every time the sun comes out, you have an issue with light contamination. Install blackout material upstream and downstream of your sensor—it may be necessary to do so for quite a distance—to prevent ambient light from being a problem.
• Preventative Maintenance. Older style UV photometers are prone to continual baseline drift primarily because of the mercury vapor arc lamps being used for the light source. These light sources have a very short lifetime compared to modern solid state LED sources, so should be replaced often. They emit a lot of energy at 256nm (regardless of the wavelength being measured) and this caused solarization to bandpass blocking filters that remove the light outside of the wavelength of interest. With the fairly rapid decay of the lamp and the solarization of the filters, the linear range of the measurement soon changes from perhaps 0 - 1.5A to 0 – 0.5A and this has a tremendous effect on accuracy, particularly in high concentration applications. It is vital that frequent validation of the instrument’s measurement capability using certified reference standards is carried out to identify when these critical optical components require changing.

The Kemtrak NIST-traceable validation filter holder lets you verify photometer performance quickly and without pulling the flow cell out of the line. It accepts either certified NIST-traceable reference filters or liquid samples, giving you a simple way to confirm the instrument is operating within spec during routine checks.

The holder can be factory-mounted on the optical flow cell or supplied as a standalone unit in the fiber-optic chain. It uses standard 10 mm cuvette-style NIST absorbance filters—the same format commonly used in laboratory spectrophotometers—so you can rely on familiar, proven reference materials.

Key benefits include:

• Quick verification of measurement accuracy
• Standard 10 mm cuvette format
• Uses the same NIST filters already used in the lab
• Direct cross-validation between lab spectrophotometers and Kemtrak in-line photometers
• Ability to check liquid samples
• Accepted by major quality systems including GLP, ISO 9000, and ISO/IEC 17025

Each DCP007-UV absorbance photometer consists of an electronics unit configured for wavelength, an inline measurement cell with the optimum optical pathlength for the application, and a pair of high quality fiber-optic cables.

Each UV SPECTRA inline absorbance spectrophotometer consists of a Xenon light source module, a compact detector module, and an inline measurement cell with the optimum optical pathlength for the application. Plug in connection cables are selected for length required. Optional items include a touch screen HMI for configuration and local readout, communications gateways, and various modules for discrete analog and digital I/O.

In its standalone form, the UV SPECTRA unit draws power through PoE from its network connection. When used with an HMI and/or other optional modules, a 24Vdc power supply is required.

Cleverly designed amplification stages around the photometric detection circuitry of the DCP007-UV allows for linear absorbance performance with full measurement resolution up to 3A and an overall measurement range of up to 4.5A. This impressive measurement range ensures effectiveness in high OD applications, without compromising process flow rates.

UV absorbance photometers (also called UV analyzers or UV monitors) measure the amount of light absorbed by materials in solution at specific UV wavelengths. They are widely used in biotechnology and bioprocessing to monitor the presence and concentration of expressed proteins and other UV-active compounds following separation steps.

The Kemtrak DCP007-UV is an advanced dual-wavelength photometer designed for accurate in-line UV absorbance measurement. It uses precision fiber optics to transmit light from a solid-state UV LED source through the sample cell and back to the detector, enabling real-time concentration calculations. With no electrical components in the inline cell, the DCP007-UV is compact, safe for hazardous areas, and easy to integrate into process lines. It provides a cost-effective solution for continuous flow stream monitoring.

Traditional UV photometers often use mercury vapor lamps, which expose the process to high-intensity broad-spectrum UV light and heat. This can degrade valuable product, create unknown byproducts, and lead to systematic measurement drift due to lamp aging and filter erosion. The DCP007-UV avoids these issues by employing low-power, wavelength-specific solid-state LEDs. These LEDs deliver thousands of times less energy than conventional lamps, eliminating thermal or photochemical damage, and are available at discrete UV wavelengths from 250 nm upwards.

The instrument’s proprietary dual-wavelength design, along with advanced digital electronics, allows measurements up to 4.5 AU (1 cm path length) at two discrete wavelengths. Optional shorter path lengths enable even higher optical density measurements. Hygienic, zero-dead-volume inline cells are free of electronics or moving parts, making them ideal for hazardous environments. In-line verification is possible using the Kemtrak Absorbance Photometer Traceable Verification Accessory, which allows calibration with the same NIST-traceable standards used in laboratory instruments, providing direct correlation to offline methods.

Typical applications of the DCP007-UV include:

• Chromatographic separation monitoring
• Micro- and nano-filtration process control
• Concentration measurement of aromatic solvents

With its combination of solid-state UV LEDs, precision optics, and advanced electronics, the DCP007-UV delivers unmatched performance for in-line UV absorbance measurement and peak detection in industrial processes.