How to Use a Spectrometer for Your Application

Know the Application of the Analytical Instrument

Despite being extremely important, the specification of design qualification (DQ) is usually underrated. With the help of the DQ, customers can make sure that the instrument has the required functions and performance criteria to be used for their application. Moreover, an appropriate design qualification will help to isolate the important from the less important features and enable the customer to survive in the “battle of features”, which is waged from suppliers onto the customer.

To determine design requirements it is helpful, if customers can specify the application they want to use the spectrometer for. Ask yourself: What is the primary issue or the primary function to solve? Do I need to test fuels for material specification? Do I need to improve the blending process? Or do I have to conform to transport or governmental regulations? Specifications should follow this purpose, and reflect the user needs.

Moreover, design qualification should include very simple design questions. For instance, Should a fuel truck driver be able to determine fuel quality with the instrument? Or is the analyzer bought for a skilled spectroscopist? The requirements for these user groups will be quite different.

Get to the Core Purpose

An initial step for the specification is to get to the main purpose. While spectrometers are capable of measuring several liquids, a qualified spectrometer is already arranged to suit a particular purpose. For instance, a Grabner fuel analyzer is already designed to determine jet fuel, diesel, and gasoline, but it is not designed to measure solvents or wastewater.

The instrument is still capable of measuring more than 100 fuel parameters directly from the spot, by using strong and proven fuel data from sources across the globe for analysis. Yet, all these parameters will not be relevant for users’ application, and usually, a limited range of parameters needs to be analyzed. Therefore, it is essential to determine if a technique for a new parameter can be added to the analyzer or if the relevant parameters are covered in the standard setup.

It is also significant to define the type of fuels users want to use the analyzer for. The users’ instrument might be able to measure finished gasoline, but could non-regular fuels like base gasoline or Naptha also be tested without oxygenates?

Probably, some modifications may need to be made to the basic analyzer setup. Users’ supplier should be able to help them with setting up a dedicated Naphta database to enhance their results.

Specifying Operation and Performance of an FTIR-Analyzer

Operational Qualification (OQ) is more complicated to verify and specify compared to the design qualification. Performance criteria determine the type of technical aspects that need to be fulfilled by the instrument to obtain the required operational performance. For instance, operation requires that an instrument should use less than 25 mL sample for a normal run. For the reasons of accuracy and speed, the instrument is required to be an FTIR analyzer with an optical resolution of 4 cm^-1. For a reliable absorbance detection and good signal detection, the instrument should have a Ge-coated KBr as material for the beam splitter, the light source should have at least 1000 °C, and the cell should be made of ZnSe. For quantification of FAME in diesel, the instrument must use a 100 µm cell as this is required by diesel specifications.

At the time of OQ, performance requirements must be testable, when employing traceable standards and a calibrated instrument. A requirement could be to check whether the instrument is capable of achieving repeatability as per ASTM D5845 oxygenate specifications when 4% EtOH concentration is measured in gasoline or whether the detection limit satisfies the EN 238 benzene requirements during day-to-day analytical use.

Specify Sensible Criteria

As stated, a good specification is designed in accordance with the purpose of analyzer use. Technical specifications are also included in this. Usually, specifications are either irrelevant to the job they are intended for, or look too good to be true. The following are examples of specifications that are unrelated to the purpose.

Example 1: A customer is denoting a Limit of Detection (LOD) of 1 g/L for aniline measurements for an FTIR spectrometer using a 100 µm cell. On the contrary, the relevant governmental standard concedes that the spectrometers will not be able to accurately identify or measure less than 3 g/L aniline content.

Example 2: When the optical resolution of a mid-infrared analyzer is debated, the perception usually prevails: The result will be better if the resolution is also better.

However, does a resolution of 2 cm^-1 have benefits above a resolution of 4 cm^-1? It is plausible because component peaks similar to each other can be more readily differentiated (FAEE and FAME). However, another fact holds true: better resolution translates to higher spectrum noise. Therefore, the optimal resolution is the one that enables a strong identification of fuel components in the mid-IR spectrum and minimizes baseline noise to a rationally low level.

Specify Requirements to a Supplier Such as AMETEK Grabner Instruments

The number of available spectrometers is growing and the instruments are becoming increasingly complex. Therefore, it is important to extend specifications on supplier requirements. Preferably, the supplier’s salesperson works as a trusted mentor for the customer and helps with identifying meaningful specifications and applications. The concerned salesperson enters into the discussion with the customer to find out:

• Which specifications are needed to achieve the required performance
• Which limits cannot be achieved
• What application the analyzer is used for
• If an existing analyzer setup has to be altered to fulfill these specifications

Sales managers and distributors of AMETEK Grabner Instruments work as the perfect trusted adviser. The company performs a demonstration at the customer site and runs tests, does OQ and IQ with the customer, answers application questions, offers overall training and after-sales support, performs basic troubleshooting, and provides a way for after sales support via defined processes.

As a supplier, AMETEK Grabner Instruments is capable of satisfying all these requirements and is in a good position to win the long-term trust of customers.

This information has been sourced, reviewed and adapted from materials provided by Grabner Instruments.

For more information on this source, please visit Grabner Instruments.