Analytical Instrumentation 9
mm for Range B. For Range A, mineral diesel was used for the background while for Range B, the open beam was used. The flow cell was drained between samples and then rinsed with approximately 3 mL of the next sample prior to use. This rapid cleaning procedure reduces carryover to negligible levels and allows a total sample measurement time of about 2 minutes.
The calibration model was built using Spectrum Beer’s Law software following the parameters specified in EN 14078:2009. The results are shown in Figure 2. Excellent linearity and precision were obtained over both ranges, and the SEPs were about a factor of 2 – 3 better than obtained with the ASTM D7371 method.
ASTM D7371 specifies the concentration ranges that must be used for the calibration. The resulting calibrations are not suitable for routine measurement of concentrations below 1%. However, good spectra of significantly lower concentrations can be measured using an ATR accessory, as shown in Figure 4. A realistic detection limit for this method is approximately 0.5%
Figure 4. IR spectra of the biodiesel standards measured using a PerkinElmer Biodiesel IR FAME Analyser system with 9-reflection diamond UATR accessory, and the Beer’s Law calibration plot.
Other Considerations for Method Implementation Figure 2 Calibration results for EN14078 using the Spectrum Two FT-IR spectrometer.
Both of these methods provide excellent performance for blend analysis. EN 14078 offers slightly better precision and a simpler calibration procedure, but at the cost of slightly greater analysis time per sample.
Detection Limits: Suitability for Trace Analysis
EN 14078 affords excellent sensitivity by the use of a long pathlength transmission cell. Spectra of some low-concentration samples are shown in Figure 3. The difference between 0 and 0.01% FAME is clearly visible, and the detection limit estimated as 5 × SEP is 0.003% (30 ppm). However, this assumes that a suitable FAME-free reference is available, and the real detection limit may be somewhat higher if variability in the mineral fuel is encountered.
For routine use, the ATR accessory permits slightly easier sampling in practice than other methods, since only a very small volume of sample is required and the accessory is easy to clean. The transmission method can be streamlined significantly by using a flow cell and disposable syringes. Initial qualification of the ASTM method requires measuring a large number of standards in order to verify that the chemometric model is performing adequately.
Conclusions
Figure 3. IR spectra of the biodiesel standards measured using a PerkinElmer FT-IR spectrometer and Fuels FT-IR Application Pack.
Analysing the concentration of biodiesel in distillate fuels is becoming increasingly important, both to verify blend concentrations and to detect trace levels of FAME in supposedly pure distillate. As such, a rapid and precise method quantification of FAME in diesel fuel blends is essential - FT-IR spectrometry offers just that. As demonstrated here, very low levels of biodiesel can be detected in diesel samples using FT-IR spectroscopy. Although both ASTM D7371 and EN 14078 methods are equally effective for standard blend measurements (1% to 30%), the better sensitivity attainable with a transmission measurement gives EN 14078 the edge over ASTM D7371 for trace measurements, with a detection limit of tens of ppm demonstrated here. Both methods are very easy to use with support from modern instruments and intuitive software.
New Spectrum Two™ Spectrometer for High-Speed Infrared Analysis
PerkinElmer Inc., (USA) recently announced the launch of Spectrum Two™, a reliable infrared (FT-IR) spectrometer built upon decades of spectroscopy expertise. Part of a new platform of FT-IR spectrometers, Spectrum Two is designed specifically to perform rapid analytical measurements and is suited to a wide range of materials and markets.
Easy to use and compact, Spectrum Two is ideal for unknown substance identification, material qualification or concentration determination. Spectrum Two can be operated across applications as diverse as fuel and lubricant analysis, pharmaceutical, nutraceutical, environmental and polymer analysis, and the teaching of these methods in academic laboratories.
The instrument's low-maintenance design breaks new ground in operational simplicity and is intended for use by "anyone, anywhere, anytime" - bringing the benefits of accurate and reliable high-speed FT-IR analysis to non-expert users, even in non-laboratory environments.
Dusty Tenney, president, Analytical Sciences and Laboratory Services, PerkinElmer, stated, “More than 65 years of PerkinElmer spectroscopy knowledge have been distilled into Spectrum Two to provide an instrument that verifies the quality of materials – fast. This out-of-the-box solution meets the exacting requirements of many applications and will grant customers absolute confidence in their infrared results."
Dedicated systems utilising Spectrum Touch™ next-generation user interface have also been developed to meet the needs of application-specific quality control analysis. Incorporating user-friendly touch screen technology, Spectrum T ouch allows results to be obtained faster than ever before by even the most inexperienced user, simplifying analysis operations considerably.
The instrument's innovative software and patented features ensure consistency and repeatability, and a unique humidity shield protects against environmental effects.
The Spectrum Two analysers also represent a major milestone of PerkinElmer's Corporate Social Responsibility initiative, through reduction of the overall carbon footprint of manufacture, packaging and transportation. These are the first PerkinElmer instruments where reducing the impact on the environment was integral to the design process, by creating the smallest and lightest PerkinElmer infrared instruments ever made and selecting materials from recyclable sources. This design philosophy will also help customers reduce their own carbon footprint and operating costs by minimising the instruments’ power consumption.
Reader Reply Card No 26
New Heated Oil Test Centrifuge
Koehler Instrument Company (USA) is pleased to introduce our redesigned Heated Oil Test Centrifuge. Our latest model centrifuge incorporates the accuracy and precision of our previous model with enhanced features such as a user friendly LCD Touch Screen Control Panel. The control panel not only controls the speed at which the centrifuge rotates but can also be used to turn the heat on and off, set the duration of the test and choose the type of rotor assembly and corresponding glassware to be used during the test. A choice of Long, Short, Pear and Finger tube rotor assemblies and glassware are available to meet laboratory requirements.
Additional improvements from the previous model include a motor speed mechanism that calculates an RPM value based on the User defined parameters for RCF setting and type of rotor selected. The Centrifuge features a large, top opening lid providing easy access to the rotor and tube holders and for cleaning of the unit. The lid has an 18 ½” diameter viewing window allowing the operator to monitor the samples throughout the test run.
Ensuring safety while providing the latest equipment to the petrochemical industry is our goal and to this end we have incorporated various features. The centrifuge is equipped with a Safety Lockout Mechanism, a Nitrogen Purge feature, and has been manufactured to meet the Class 1, Division 2 explosion resistant rating.
Reader Reply Card No 27 February / March 2011 •
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