Concentration Measurement Solutions

Water has a strong absorption throughout the entire NIR band with absorption peaks at approximately 1440nm and 1930nm. The lack of absorbance in alcohol and many solvents makes these wavelengths optimal for water in solvent measurements.

• 1440nm is recommended for water measurements from 0 - 100% water.
• 1930nm is recommended for trace (ppm) water measurements.

Typical applications for the DCP007-NIR include:

• Solvent concentration
• Moisture content analysis
• Water in alcohol monitoring
• Chromatography gradient control (solvent mixing)
• Residual solvent concentration in pharmaceutical processing
• Solvent recovery
• Replacement for Karl-Fischer titration

NIR is a preferred technique for accurately determining water in solvent concentrations on line, primarily because of the high degree of accuracy achievable. Inline measurement cells are configured with an optical path length to optimize performance across the desired operating range. The DCP007 generates stable, drift free measurement to provide high confidence and trouble-free operation over long periods of time.

The DCP007-NIR measures intensity changes due to absorbance by water content. It does this by generating a stable level of NIR energy at a specific wavelength which is re-measured after it has passed through the liquid to determine how much has been absorbed. Water content in the flowing stream is directly proportional to absorbance. As a further option, a temperature input is available to allow compensation of the measurement to a standard temperature - removing variations due to temperature if necessary for the application.

Two versions of the DCP007-NIR are available:

• LED energy source: Suitable for bulk water content measurement across a range of 0 to 100%
• Thermopile energy source: Designed for the measurement of trace (ppm) water levels

The analyzer can be connected to any one of the many styles of flow-through optical measurement cells from Kemtrak. For tank or large pipe applications, third-party fiber optic probes can also be used, usually without any special configuration or calibration requirements.

Laboratory spectrophotometers are designed for the analysis of discrete samples in controlled conditions. The DCP007 is engineered for continuous, unattended operation directly in the process stream, an industrial environment including high pressures, temperatures, vibration, and chemically aggressive media. Key differences include:

• No sample preparation or conditioning required
• Continuous real-time output rather than periodic discrete measurements
• Stable, drift-free performance over extended periods without recalibration
• Designed for direct connection to process pipework via inline measurement cells or fiber optic probes

The DCP007 operates on the Beer-Lambert law of optical absorbance. A stable, controlled light source generates energy at a specific wavelength which passes through the process liquid via a flowing measurement cell. A detector measures the intensity of transmitted energy returned to the analyzer; the reduction in intensity relative to generated energy is directly proportional to the concentration of the absorbing component. Because the instrument measures absorbance rather than a derived or inferred property, it is inherently linear and straightforward to calibrate against known standards.

The DCP007 is always supplied in a dual wavelength configuration.

• In single wavelength operation, it measures light absorbance at one selected wavelength, providing concentration measurement of a target component. This is a typical configuration for most water-in-solvent and concentration monitoring applications.

In dual wavelength operation, the DCP007 measures absorbance at two wavelengths simultaneously. The ratio or difference between the two channels can be used to compensate for background interference such as turbidity, color variation, or the presence of a second absorbing component, for a marked improvement in measurement accuracy in more complex process streams.

Path length selection is determined by the expected concentration range and the molar absorptivity of the target component at the measurement wavelength. As a general principle:

• Higher concentrations require shorter path lengths to keep absorbance within the linear range of the Beer-Lambert law (typically 0.1–2.0 AU)
• Trace-level measurements require longer path lengths to generate a detectable absorbance signal
• For water-in-solvent measurements at 1440nm, path lengths typically range from 1mm to 10mm depending on the concentration range
• For trace water at 1930nm, longer path lengths are used to detect ppm-level concentrations

Kemtrak offers a wide range of measurement cell geometries and path lengths. The appropriate path length for a specific application can be confirmed with Kemtrak based on the target concentration range and process conditions.

Yes. In addition to inline flow cells, the DCP007 can be connected to third-party fiber optic probes for insertion directly into tanks, vessels, or large-diameter pipelines. This configuration is typically used where inline flow cell installation is impractical. In most cases no special configuration or calibration is required beyond that needed for a standard flow through measurement cell installation, as the DCP007 electronics compensate for fiber optic transmission characteristics automatically.

Kemtrak measurement cells are available in a range of process connection types and wetted material configurations to suit different industries and process chemistries. Common options include:

• Wetted materials: 316L stainless steel, Hastelloy C-276, PEEK, and other chemically resistant alloys and polymers
• Process connections: Tri-clamp (hygienic/sanitary), NPT, ANSI flange, DIN flange, and custom configurations
• Window materials: Sapphire and other optical materials suited to specific chemical compatibility and pressure requirements
• Pressure ratings: Cells are available for both low-pressure and high-pressure process applications

Material selection should be confirmed against the specific process chemistry, temperature, and pressure conditions.

The DCP007 analyzer is designed for straightforward industrial installation. Key requirements include:

• A suitable inline flowing measurement cell or probe insertion point in the process line
• Adequate flow velocity through the cell/past the probe to ensure representative sampling and prevent air bubble accumulation
• A stable power supply
• Signal wiring to the control system (4–20mA analog output(s), Modbus RTU)
• For hazardous area installations, compliance with regulations and the use of an appropriately certified enclosure

No external purge gas, sample conditioning system, or compressed air supply is required.

The DCP007 provides absorbance as a base measurement and this can be calibrated/correlated to application measurement units to provide a meaningful output. This involves measuring a series of known standard solutions across the expected concentration range and correlating the absorbance readings to those concentration values. The allows a calibration “curve” to be produced and this is stored in the instrument. In a great many cases, the “curve” is linear and correlation requires only two points. In practice:

• Initial calibration is typically performed at commissioning using prepared standards or process samples of known concentration verified by laboratory analysis
• For water-in-solvent applications, calibration is very straightforward and stable over long periods
• Temperature compensation can be applied using an optional temperature input to remove the effect of process temperature variation on the measurement
• Recalibration is rarely required unless process chemistry changes significantly
• Calibration verification is easily carried out using hard media absorbance filters inserted in the light path – no need for solutions

Yes. The DCP007 can be provided within a certified hazardous area enclosure for installation in locations classified for flammable gases, vapors, and dusts. This makes the DCP007 suitable for direct installation in chemical plant, solvent recovery, distillation, and pharmaceutical manufacturing environments without the need to locate the analyzer in a separated ordinary area.

Inline measurement cells are fiber optic connected and have no electrical or electronic components onboard. This makes them absolutely suitable for hazardous area installation and they can be connected with long fiber optic cables to a remotely installed analyzer in an ordinary area if preferred.