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NEW ZEALAND BEEKEEPER, JUNE 2017
MPI MANUKA CHEMICAL MARKERS TEST What is the background to the test? MPI’s Mānuka Chemical Marker test looks for naturally occurring chemical compounds in honey samples that are also known to be found in mānuka nectar. As honey is primarily made from nectar, these chemical markers confirm that the honey includes enough nectar from mānuka to be called a monofloral or multifloral mānuka honey. Quality control Laboratories carry out checks each time that they analyse samples for quality control purposes. In the case of chemical marker testing, these will include: • Blank QC samples, which should have nothing in them, and therefore check for contamination in the lab. What results come from it, and how do I understand them? Results are reported in milligrams per kilogram (mg/kg) in the honey. One mg/ kg is sometimes called a ‘part per million’ (there are one thousand milligrams in a gram, and one million milligrams in a kilogram). These are the same units used to report other tests that the honey industry may be familiar with—tutin, DHA, MG, HMF, and leptosperin. • Control samples, which include honey samples the lab uses repeatedly, and
How is it done? The Chemical Marker test uses a technique called ‘liquid chromatography–tandem mass spectrometry’ (LC-MS/MS), which is used for other tests such as tutin. The test requires one to two days to complete from start to finish. The equipment needed is quite expensive (over $600,000), but the preparation process is relatively inexpensive in terms of both labour and consumables. Labs are tending to charge $90–$100 + GST per sample. Weigh and dilute the honey sample – after weighing some honey into a testing tube, it is dissolved and diluted with a pre-prepared extraction reagent. This prepares the sample for analysis, putting it in the right condition to be run on the mass spectrometer. Analyse the sample on the mass spectrometer – the diluted honey is put into small vials and analysed on the mass spectrometer. Liquid chromatography is used to separate the various compounds found in the sample, before the concentration of those compounds is measured by the tandem mass spectrometer. All four of MPI’s chemical markers are able to be analysed in the same run through the instrument if the lab wishes to do so. Results are reviewed and approved for reporting – the mass spectrometer produces a result for each of the samples that have been tested, which is reviewed by a member of the lab team. After confirming they are satisfied with the results, and with quality control samples, they are approved for reporting. A summary of the testing process is:
samples which have had known amounts of the chemical markers added to them by the lab. The lab will know what results to expect for these honeys and will check this when reviewing results. • Duplicate samples, which may be the same sample tested twice in the same batch, or may be a sample from a previous batch that is re-tested. The purpose is again to confirm that the testing is producing consistent results using a ‘live’ sample submitted by a customer. • An internal control (or system monitoring compound), which confirms that the preparation and analysis process has gone well. A known amount of this internal control is added to each sample during preparation, and the lab expects to see this in the results for that sample after testing. If the amount of systemmonitoring compound is low (or high), it is an indication that the sample may need to be retested.
To interpret the results for a sample, simply compare them to the levels in MPI’s proposed definition. However, if you have a result that is close to the minimum level required by MPI, there is a chance that a re-test of the honey may see that result change to fall below that minimum level due to the variability in honey samples and in testing methods. See comments earlier in this article. This is particularly important for the three chemical markers that have a required level of 1 mg/kg (which is very close to the method’s reporting limit). In this case, we suggest that a result of 1.5 mg/kg or lower is treated as being at risk of failing if re-tested in future. Left to right: Analytica technicians Luca and Kris with the AB Sciex 6500 mass spectrometer, used for analysis of compounds like tutin and MPI chemical markers in honey. Photo courtesy of Analytica Laboratories.
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