Friday, 6 January 2017

Transitioning from Flame AAS to MP-AES: benefits and advantages...by Emmanuel Chidiwa Mbewe

Emmanuel with 'A Practical Guide to ICP-MS'.
My name is Emmanuel Chidiwa Mbewe from Lilongwe University Agriculture and Natural Resources in Malawi. I work as a Chief Technician in Soil Sciences within the Department of Crop and Soil Sciences. Currently I am undergoing a Commonwealth Professional Scholarship with the Inorganic Geochemistry team within the Centre for Environmental Geochemistry, during which I have experienced modern methods of laboratory analyses, systems of work, including quality assurance and overall management of tasks and data to demonstrate confidence in data output.  I also attended a meeting in London for the Commonwealth Scholarships Commission (CSC) Fellows Connect 2016 which enabled me to meet other Fellows based around the UK, to share my experiences and celebrate my fellowship. 

Before I depart for Malawi at the end of the week, I will attend the 2016 International Fertiliser Society Agronomic Conference in Cambridge to hear talks on agronomic techniques relevant to aspects of fertiliser recommendation development, the role of fertilisers in reducing emissions, grassland nutrition, and precision farming.  There will also be a presentation on the work of Grace Manzeke, the first winner of the Brian Chambers award.

MP-EAS Demonstration


A highlight of my stay was when I had a chance to visit the Reading Scientific Services on the University of Reading campus along with Elliott Hamilton, where we received a demonstration on the use of MP-AES 4210 by Agilent Technologies, in advance of a transition from use of Flame Atomic Absorption Spectroscopy (FAAS) to Microwave Plasma Atomic Emission Spectroscopy (MP-AES), which will be purchased from the Royal Society-DFID project. Both of these techniques are used for elemental determination in a variety of sample materials including soil and plant samples.

Major Advantages


Emmanuel using the MP-AES.
The MP-AES will be purchased and delivered in February 2017. The major advantages of FAAS are:
  • reducing operating cost, increasing safety;
  • improving analytical performance through improved sensitivity and;
  • multi-element capability and ease of use.
The largest running cost for level entry spectroscopy is the source gases. FAAS uses a combination of air and acetylene, or nitrous oxide and acetylene. These two gases are provided in cylinders which regularly needs replenishment. These gases are quite expensive in developing countries like Malawi. On the other hand, the 4210 MP-AES uses nitrogen that is extracted straight from the air to sustain the plasma. The Agilent 4107 Nitrogen generator coupled to an air compressor supplies all the free nitrogen required at greater than 99.5% purity. This leads to dramatic reductions in operating costs over the life of the instrument.

Safety Concerns


When using FAAS there are concerns about safety aspects because of the use of acetylene and nitrous oxide. The major concerns cover a wide range; from storage and handling of cylinders, to the use of the flame in the instrument. Presence of a naked flame is of a concern in laboratories especially those that handle organics, which are highly flammable, for this reason FAAS have to be attended to all the time. All these issues are eliminated with the use of 4210 MP-AES.

Improved Performance


Improved analytical performance comes about because there is an improvement of in detection limits for MP-AES compared to FAAS. In the case of some elements such as Ca and V this can be an order of magnitude lower. An improvement in detection limits implies that it is possible to analyse elements that otherwise have high detection limits in FAAS like phosphorus and boron. In other words, elements that cannot be analysed on FAAS are easily analysed on the MP-AES. It can also analyse up to 10 minutes at a time using the same sample volume as an FAAS. Selenium can be measured using hydride generation within the same analytical run as other samples. The higher temperature of nitrogen plasma atomisation /ionisation also improves the linear range and stability compared to FAAS.

When it comes to ease of use in MP-AES, this results from the fact that with the hotter plasma source of 4210 MP-AES, chemical interferences that are encountered in FAAS are eliminated. This means that the element specific sample preparation required on FAAS is not needed which greatly simplifies the sample preparation process.

Change from FAAS to MP-AES


With the benefits highlighted above, I look forward to moving from using the FAAS to using the MP AES.  The challenge that awaits me on my return to Malawi, is to prepare the laboratory building services in time for delivery of the instrument, which promises to vastly improve our current capability for elemental analyses, whilst keeping costs down. I won’t be alone in this challenge, partners on the Royal Society-DFID project will also be receiving an MP-AES in Zambia and Zimbabwe in February to March and we will share the training experience through collaboration and regular interaction, with support from the sales company (Chemetrix) in South Africa and colleagues from the Centre for Environmental Geochemistry (BGS-University of Nottingham).

Many thanks to Agilent and Reading Scientific Services for hosting the demonstration of the MP-AES. Thanks also to Robert Thomas who donated 50 of his textbooks ‘Practical Guide to ICP-MS – a tutorial for beginners’.  These textbooks will be given to students and technicians within the Royal Society-DFID network, as well as other partner organisations in Africa.

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