Message from the President
As advised in the last issue, Mr Bob McCowage has been appointed General Secretary for the remainder of the 20th Session following Dr Whayman’s resignation due to ill-health. Together we have considered the matters raised in the two letters to the editor published last issue. While we would encourage further discussion of the issues raised, we tender the following views as our first reaction to a few topics.
Objective of ICUMSA
Although the objective of ICUMSA has not been raised specifically, we believe that a prerequisite for the proper consideration of any major issue is a clear definition of the organisation’s purpose. If the objective is well defined, and accepted, then it can be used as a benchmark for the assessment of issues. If the objective is not clear, nor universally accepted, then the debate on issues is likely to be confused and result in conflict.
Four objectives of ICUMSA are of course stated in the Constitution.
The most definitive is objective 4:
“To agree upon and to publish international recommendations for uniform methods of sugar analysis”.
While this would appear to be a simple statement, there is undeniably some difference of opinion as to the meaning and intent of the word “uniform”. The Oxford Dictionary provides the following definition “not varying with time or place, conforming to the same standard or rule”. However, to obtain clarification of intent, we need to tum to the origins of the Commission, its raison d’etre if you like.
The Commission grew out of the recognised need for uniform methods of sampling and analysis to facilitate dealings between buyers and sellers of sugars. This was the major focus of the early work of the organisation and significant early successes were the agreements for the analysis of
– sucrose by polarisation
– water by oven drying
– ash by incineration with sulphuric acid
– invert by the Herzfeld method
In other words, single methods were agreed for the determination of particular constituents of importance to the trade in sugars. Indeed, had the focus not been on single agreed methods for particular criteria, then it is difficult to understand just what the Commission could have claimed to have achieved in respect of the requirements of those trading in sugars whose needs were supposedly being addressed.
Against that background, it is our firm belief that the main objective of ICUMSA is to agree upon and promote internationally the use of a specific method for a particular constituent or property of a sugar so that the results obtained for the constituent or property at any time, or at any place, will have a high degree of integrity and will be directly comparable.
Single versus Multiple methods
If the major objective of the organisation is agreed to be as stated above, then the answer to this question is obvious. ICUMSA must resolve the merits of competing methods of analysis for particular purposes and select one method as the Official method.
If the objective of the organisation is not as stated, if it is believed that ICUMSA has no role in ensuring uniformity of analysis for trade or legislative or other purposes, then the Commission should become a method validating body and drop the word “uniform” from its title. In considering the above, it is suggested that thought be given to where the real value of an organisation like ICUMSA lies.
Speed of response
It has been suggested that the time taken by ICUMSA to adopt Official methods is too long. Traditionally, the status of methods has only been reviewed at four yearly plenary sessions and it can take from eight to twelve years for a method to attain Official status. This criticism is accepted. The Constitution already allows for recommendations to be affected by letter ballot. This process can, and should, be activated for improving the speed of response in high priority areas.
We think that in general ICUMSA has been slow in achieving its goals.
This probably has more to do with the will to get the job done rather than the bureaucratic mechanisms of the Commission. We are highly motivated to have all methods with international ramifications properly tested and published in booklet form during the 21st Session.
We have produced for approval at Colorado Springs the polarisation of raw sugar method written up in ISO format and presented in sample booklet form. If this format is agreed to, then we will expect General Referees and their Associates to produce similar drafts for all the methods within their subjects as soon as possible. The Publications Committee will then edit and publish these methods and offer them for sale.
Steering Committee
A case has been made to have a steering committee allocate working arising out of Recommendations approved at a Session. We agree that there is a significant task in defining the jobs to be done and the priorities to be imposed if scarce resources are to be properly utilized. It seems to us, however, that employing the steering committee to do this allocating, puts it into the hands of people who do not have responsibility for executing the work. We believe that Referees need to take a responsible view of how recommended work is to be achieved before putting up a recommendation. If this is done beforehand, the Session’s approval becomes the first step in the execution process.
One of the main reasons for establishing General Refereeships in the recent re-organisation of subjects was to provide each major area of products analysis with a manager who has a working knowledge of the end users’ needs as well as being qualified scientifically to undertake the method testing and documentation. We do not rule out a future role for a steering committee, but we think that such a committee should solve extraordinary problems rather than becoming a part of the normal management process.
HPLC, a possible alternative to pol analysis for factory juices and molasses?
K.J. Schäffler
Single polarisation (pol) is probably the most frequently used and familiar analytical method applied in the sugar industry. Pol measurements have been in use for well over 100 years and can be viewed as one of the first instrumental analytical methods available to the sugar technologist. Consequently, the importance of po! is well established (even entrenched) and well known to everybody from the grower in the field, the operator in the factory to the buyer or seller in the commercial market. This universal acceptance has led to pol being adopted as a synonym for sucrose. This assumption can give rise to much misunderstanding when comparisons are made with more recent instrumental techniques. This point will be discussed later in some detail. Pol has the following strengths and weaknesses:
– Historical acceptance. Pol is employed for paying sugar farmers for their crop as well as for assessing the sugar factory’s routine performance. Sales of raw sugar are also based on pol. A procedure with this sort of tradition is not going to be replaced overnight no matter how appealing the advantages of any new technique may be. Even if it can be shown that pol can produce gross inaccuracies, it is often very difficult to alter legislation governing contracts especially if certain parties stand to loss financially.
– Precision. Pol is an extremely precise determination, for example the interlaboratory reproducibility has been shown to be about 0.05 units for a 98.5 VHP sugar [l]. This makes it an ideal procedure when buying and selling raw sugar.
– Calibration. The polarimeter can be independently calibrated using highly accurate quartz control plates. Thus pol calibration is not influenced by the purity of sucrose standards.
– Cost effectiveness. Pol analysis is relatively inexpensive, the only consumables are filter paper and lead acetate solution. This in turn makes it an ideal payment method for beet and cane juices. This is especially true if the factory throughput is high or if the laboratory has to deal with a large number of consignments from different growers.
– Ease of operation. The procedure is extremely simple to perform and with modern digital polarimeters, relatively unskilled staff can produce repeatable results.
– Simple sample preparation. A simple sample dilution, followed by clarification and filtration is all that is required prior to polarising the sugar solution.
This last point leads onto one of the most serious drawbacks of the pol determination. The need to clarify the solution so that a clear filtrate is presented to the instrument leads to problems on at least two counts:
– Clarification can remove or modify some pol positive compounds (especially fructose and amino-acids), leading to inaccuracies.
– Clarification agents (e.g. lead acetate) are generally toxic and are coming increasingly under fire in today’s pollution conscious environment. The search for alternative non-toxic substitutes is complicated by the unknown effects of these salts on non-sucrose constituents.
These last two points indicate that although pol is clearly extremely precise it is not necessarily accurate and is readily influenced by optically active compounds in the mixture. This limitation is obviously linked to the purity of the products being analysed. Technologists have been aware of po! inaccuracies but convenience and simplicity have overridden these reservations until now. Increasing legislation, forcing the abandonment of traditional lead acetate clarification, is perhaps the impetus required for the adoption of high-performance liquid chromatography (HPLC) techniques for juices, syrups and molasses products [3].
As alternative clarification agents are going to bias the current pol determination anyway, HPLC offers many advantages to the factory technologist:
– Accuracy. Sugar samples subjected to HPLC are separated on an analytical column. Polysaccharides, oligosaccharides and monosaccharides are all separated from each other and from non-sugar constituents. This fractionation prior to quantitative measurement results in a far more accurate estimate of sucrose, especially in low purity products. Even in relatively high purity cane juice, detailed comparisons [4] have shown that pol nearly always underestimates sucrose, the difference between them vary from one factory to another, from month to month and from season to season. These differences are even more significant in low purity products where the pol/sucrose ratio can vary from 0.8 to 1.05. HPLC would avoid these inaccuracies which not only affect payment to growers but also bias factory control data and produce anomalous results in the fermentation industry.
– Precision. For factory juices and molasses samples the precision of HPLC is similar to pol (1, 2]. The repeatability of the technique can only improve with the fairly recent introduction of computer-controlled autosamplers, pumps and detectors.
– Additional information. Because HPLC first separates components and then measures their concentration, it is capable of yielding more information than direct pol. In cane products, sucrose, fructose and glucose can all be determined with adequate precision. Accurate determination of glucose and fructose is useful for estimating inversion in factory front-end juices. In addition, it is possible to obtain an estimate of the total trisaccharide present [2]. It is also possible to determine the betaine content of beet molasses [5]. Ethanol and glycerol can also be estimated, this is especially important for distilleries [ 6). HPLC can also be used to measure low levels of ethanol in juices to determine cane delays between cutting and crushing [7].
– Nontoxic. HPLC of sugars on cation exchange columns is a nontoxic procedure as water is used as the mobile phase.
– Automation. HPLC lends itself to automation. After sample weighing and dilution, a tiny quantity is filtered into a vial. Sample injection, separation and measurement are all carried out automatically. Large runs can be initiated and left to run inattended.
– Trace sugars. With modem, refractive index detectors and especially with the new pulsed amperometric detector, sugar losses due to entrainment or spillage can easily be monitored.
At the 19th ICUMSA session in Cannes, two different HPLC techniques were subjected to an inter-laboratory test in conjunction with a gas chromatographic (GC) method for the determination of sucrose in beet and cane molasses. The GC procedure became an official ICUMSA method, whilst the two HPLC methods produced very promising results (no significant difference between GC and HPLC results). Both HPLC procedures received tentative status (2). During the current session, the main objective of subject 9, HPLC, is the simultaneous determination of sucrose, glucose and fructose in cane molasses using a cation exchange HPLC procedure. Collaborators have been asked to analyse six cane molasses samples for sucrose, glucose and fructose by HPLC. The molasses samples are diluted to 1 %, passed through a membrane filter and chromatographed.
A large number of associate referees agreed to participate. To date response has been most encouraging. Results have been received from Czechoslovakia, Japan, Hungary, France, South Africa, Italy, the United States and the United Kingdom. Once all the results have been received, the repeatability and reproducibility of the procedure will be tested statistically. An official ICUMSA HPLC procedure would be most useful especially for trading of cane molasses. The method would also be useful for comparing the technical performance of individual sugar factories.
HPLC has a definite future in both the beet and cane sugar industries. The polarimeter will still be required for the analysis of raw or technical sugar where sample dilution prior to HPLC can lead to unacceptable scatter. The success of HPLC for routine analysis will depend on reducing running costs as well as training of laboratory staff. Effective utilisation of the additional information will also be of key importance to HPLC’s success.
References
1 Mellet. P. Lionett, G, Kimmerling. Z. and Bennett. P.: Standards for the analytical precision of sugar and
molasses. SASTA 1982, 55
2 Anon.: Sucrose in factory and refinery products excluding beet, cane and crystalline products. Subject 8,
ICUMSA 19th session 1986, 94-148
3 Anon.: Sucrose in sugar beet. Subject 9, ICUMSA 19th session 1986, 149-163
4 Schäffler, K.J., and Morel du Boil, P.O.G.: Review of GC in SA Sugar industry. Sugar Technol. Rev. 11
(1988) 95-185
5 Rajakyla, E., and Paloposkim, M.: Determination of sugars and betaine in molasses by HPLC. J. Chrom. 282
(1983) 595-602
6 Clarke, M.: HPLC in the sugar industry. Sugar Azucar 1985, 21-25
7 Lionette, R., and Pillay, J.: Ethanol as an indicator of cane delays under industrial conditions. SASTA 1988,
9-11
Editor: R. Pieck, Klein Spanuit 9, B-3 300 Tienen, April 1990 – Tel. +32 16/81 24 36 – Telex 222 51 – Telefax +31 16/82 03 17.