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Kent Scientific Services, a public analyst laboratory, has selected a Stuart STR4 rotator from Bibby Scientific to meet the requirements of its fertiliser enforcement analysis work.

The prescribed analysis methods for checking the nitrogen and phosphorus content in fertiliser samples require flasks to be mixed end over end at 35-40rev/min.

Nitrogen (N), phosphorus (P) and potassium (K) are the three primary nutrients needed in large quantities by plants.

Manufactured fertilisers, used to supply crops with the nutrients that the soil lacks, have to be labelled with three figures indicating their NPK content.

The Fertilisers (Sampling and Analysis) Regulations 1996 requires the figures to be checked by standardised analysis techniques.

Kent Scientific Services provides scientific and calibration services for local authority enforcement agencies, including the analysis of fertiliser samples collected by local Trading Standards officers from manufacturers’ premises or at the point of sale.

David Heath, quality manager/toxicology manager at Kent Scientific Services, said: ‘When our old rotator broke down, we needed to find a new one capable of providing the rotation speed specified by the regulations.

‘The prescribed analysis methods for soluble N and P require fertiliser samples to be mixed with 400ml of water in a volumetric flask and mixed by end-over-end rotation at 35-40rev/min.

‘The speed we needed was well within the range offered by the STR4,’ he added.

According to Heath, the Bibby Scientific engineering department adjusted bracket on the rotator so that it would work with the large 500ml flasks that the company needs to use.

Bibby Scientific also extended the length of the bar to enable Kent Scientific Services to mix four rather than two 500ml flasks at once, enabling a control to be processed alongside three samples.

‘The STR4 incorporates a useful timer, which we set in order to mix the fertiliser samples for precisely 30 minutes, as specified in the regulations,’ said Heath.

The Stuart STR4 drive unit accepts a choice of five drums designed to take test-tube holders, plates, racks of micro-centrifuge tubes, conical flasks, reagent bottles or jars and paint tins measuring up to 200mm in length and 120mm in diameter.

The rotation speed is variable from 6rev/min to 60rev/min for a range of mixing applications and the unit can be run in continuous operation mode or with the analogue timer set for 10-60 minutes.

Bibby Scientific

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