Because of the need to use UV-digestion of water samples, we have developed a relatively simple system. We get the housing made at the University workshop and components at various companies. We have several in stock and can supply these. The cost is low due to its simplicity. The apparatus is perfectly suited for sample preparation prior to voltammetric analysis or any method requiring removal of dissolved organic matter (total phosphate analysis for instance). Any profit that is  made is used for further research. The description and cost are shown below. To order one, just email me.

Description of UV-digestion apparatus

UV-irradiation is suitable for the destruction of dissolved organic material in natural waters including seawater. This kind of treatment is a prerequisite for the determination of total dissolved metal concentrations using voltammetry, total phosphate concentrations using UV-visible spectrophotometry, total mercury determinations by fluorescence or atomic absorption spectrometry and other applications. An important advantage of this type of digestion is that there is no need for reagent addition and it can be done in clean conditions.

The lamp has been designed and tested by the Marine Electrochemistry Group, Department of Earth and Ocean Sciences. The housing is made of heavy duty PVC with a PTFE top with holes to hold quartz sample tubes. UV-light is provided by a high-pressure mercury vapour lamp with a power output of 125 W, peaking at ~250 nm. This system has been used over many years in our laboratory: it has been optimized and works for years.

Water samples are arranged around the UV-lamp in fused-silica tubes with PTFE cap.  Continuous sample flow with irradiation can be arranged by placing a silica coil around the lamp (the silica coil can be provided as an option). The lamp housing has slots for 4 silica sample tubes. The sample tubes are made from high quality fused silica.  Additional tubes can be ordered separately. Each sample tube holds up to 30 ml and is capped by a PTFE capping unit (ring + screwcap). Larger tubes holding up to 40 ml can also be supplied.

The lamp is driven by a powersupply (220-240 V) with a special plug which is protected against short-circuits (press reset to start). The lamp lasts for years under normal use, but the output could gradually decrease; 1000 hours of use is a good guide to start checking. If lamp degradation is suspected, it can be replaced by removing the PTFE top of the housing and unscrewing the lamp from the fitting. Replacement lamps can be obtained from us. The replacement lamp is then screwed in place.

Installation and use

The UV-systems produce ozone, which should be vented from the laboratory by placing the UV-system in a fume-hood. The UV-light is detrimental to the eyes. The system should therefore be screened with the supplied screen and by lowering the glass or Perspex screen of the fume hood to below eye level. The UV-lamp should be switched off prior to removing or inserting the sample tubes. The usual plastic or glass screen in front of the fumehood should be sufficient to screen the UV light, but it is not recommended to attempt to look into the system when on.

It takes a few minutes for the lamp to reach maximum light output. It may take several minutes to re-start a hot lamp which has just been switched off. It is normal for the irradiated samples to get hot; they can typically reach 80 oC after 45 min radiation. Care should be taken when using longer irradiation periods as this could cause the samples to boil and leak out of the sample tube. It might be better to repeat the irradiation after a cooling period, if you require very long irradiation for instance to destroy samples with an unusual amount of organic matter (see below).

Use of silica sample tubes

The outside of silica sample tubes should be cleaned with methanol to remove organics as these will lower the passage of UV-light to the sample.  It helps to wear gloves when handling the tubes, and to avoid touching the tubes below the neck.  The usual cleanliness is required to avoid contamination of samples with trace metals due to carry-over: rinsing or soaking of the tubes with dilute acid and distilled water is recommended between samples, unless you are conditioning the tubes with pH8 seawater.

Irradiation times

We normally use an irradiation time of 45 minutes for our samples, but this could be extended depending on the sample composition. For instance, 5 ppm humic acid is destroyed in 30 minutes. Up to about 8 ppm humic acid is destroyed in 45 minutes. Hydrogen peroxide can be added (10-50 L 30% H2O2 /10 mL sample, depending on the organic concentrations) to aid the oxidation at high levels of organics and we successfully oxidized 100 ppm humic acid in this condition. The dissolved oxygen (and added hydrogen peroxide) in seawater is known to be used up within an hour due to production of hypochlorite from chloride. This hypochlorite can interfere with the determination of certain metals using voltammetric techniques [1]; it is unstable and disappears within minutes at neutral pH, but it is more stable at low pH. The UV-oxidation of very high concentrations of organic matter can be aided by repeated addition of hydrogen peroxide at 60 min intervals.

Reference

[1] Achterberg, E.P. and C.M.G. van den Berg, 1994. In-line UV-digestion of natural water samples for trace metal determination using an automated voltammetric system. Anal. Chim. Acta, 291: 213-232.

What is supplied

Cost of UV-digestion system (complete):1,950 Euro.

Consists of:

Lamp housing, power supply, 8 silica sample tubes (30 mL or 40 mL) with PTFE capping units, one lamp fitted, one spare lamp, one Perspex UV screen.

The lamp housing has space for 4 silica sample tubes of ~30 mL or 40 mL volume each.

Delivery (DHL): 75 Euro

Prices are plus VAT where necessary.

Delivery time: available now, so within a few days.

Additional silica sample tubes (uncapped):

30 mL or 40 mL: 200 Euro for 5

Additional PTFE capping units; specify tube volume: 40 Euro each

Replacement UV-lamp: 40 Euro

Further information and ordering:

Prof Stan van den Berg

Department of Earth and Ocean Sciences, University of Liverpool, Liverpool L69 3GP, UK.

Tel: +44 151 794 4096 (office)

Or: +44 7706 152270 (mob)

Email: Vandenberg@liverpool.ac.uk