One of the most important considerations when buying a new system is your applications and the impact water quality has at various stages. It’s important not only to think about your needs but those of your colleagues as the system could be shared between labs.

Critical applications and spectroscopic techniques such as HPLC, LC-MS and AA generally require the purist water - Type I.

Standard analytical applications such as the preparation of pH solutions and feed for clinical analyzers would usually use Type II water.

Generic applications such as glassware rinsing would normally use the lowest grade of purified water (Type III).

Impurities can affect different techniques in different ways so it is important to choose your system based on your particular needs. Buying a system that removes ions won’t be of use if you are having a problem with particulates.

There are five main groups of impurities seen in water - ions, bacteria, particulates, gases and organics. All of these can potentially affect the quality of analysis so their effective removal is essential. Many of the technologies available are effective for the removal of one or two of these impurity groups, but not all of them. For this reason it is important to be confident that the system you intend to buy meets your specific demands.

Ions - Some ions absorb in the UV range (e.g. nitrites and nitrates) thus affecting UV/Vis studies. Metal ions can form adduct peaks in Mass Spectroscopy (MS) detection.

Bacteria - Behave as particulates (increase back-pressure in HPLC), by-products include organics and ions.

Particulates - Damage pumps and injectors in LC applications and increase system back-pressures.

Gases - Can produce more impurities including organics and ions.

Organics - Causes noisy or drifting baselines and ghost peaks. Extensive contamination could result in shifting retention times and distorted peak shapes in chromatographic applications.

Purified water for the lab comes in three types depending on the level of purification and it is important to consider the application in which the water will be used and therefore how pure your water needs to be.

The three main types of purified water for lab use are:

Type I Ultrapure (Reagent Grade)

This type is typically used for critical applications and spectroscopic techniques such as HPLC, LC-MS, GFAA, & ICP where a high level of purity is required. It is also used for buffers and mammalian cell culture media.

Type II (Analytical Grade)

Generally this is used for more standard applications such as preparation of buffers, pH solutions, and feed for clinical analyzers.

Type III (Lab Grade)

This is the lowest grade of purified water and is used for general applications such as glassware rinsing, heating baths, and humidifiers.

The basic principle of water purification starts with the feed (source) water; generally the feed is tap/drinking water but it could also be from a central (possibly unregulated) supply. Following the purification process Type II and III water can be removed but Type I water requires a further purification stage termed polishing. The quality and reliability of Type I water is dependent on the quality of the initial purification. It is vital to use a combination of water purification technologies to effectively remove contaminants to levels required for critical applications. Which type the end user selects depends once again upon which impurities are to be removed.

Types of purification technology include:

Reverse Osmosis (RO)

A very good all round purifier with about 95% of contaminants being removed including ions, organics, bacteria, particulates & colloids, pyrogens, and viruses. Generally these systems have low operating costs and are easily maintained although the RO membrane is sensitive to plugging, fouling, piercing, and scaling.

Ion Exchange Resins

These are very efficient at ion removal but no other contaminants will be removed. These systems tend to be easy to use and relatively cheap to buy but they are susceptible to bacterial, organic and particulate contamination which can drive up operating costs.

Activated Carbon

This exists in two types: Natural AC specifically used for the removal of residual chlorine and Synthetic AC which is efficient at the removal of organics and is useful during polishing. They have a weak effect on other contaminants and natural AC may release ions and particles adding to these types of impurity. AC also suffers from the potential of bacterial growth.

Electrodeionization (EDI)

This is a technology that is very efficient at ion removal but it requires a good quality feed water (ideally via an RO system) to prevent plugging and fouling of the ion-exchange. Weakly charged ions such as dissolved CO2 and silica are more difficult to remove.

UV photo-oxidation

This reduces organic contamination but is mainly used as a polishing technique because it can be overwhelmed if the organic concentration in the feed water is too high. This technology is generally easy to use but is limited in its effectiveness on contaminants other than low level organics.

Germicidal UV

This technology is used exclusively to inactivate bacteria. It’s worth noting this will not reduce organic contamination or remove the inactive bacteria. The bacteria itself can act as particulates or break down releasing endotoxins which may interfere with your intended application.

It is important to consider the amount of water used in your lab and to buy a system that matches your requirements. If you need 2 liters per day then a system that produces 30 liters per hour may not be for you. You should also consider when your water demand might peak and to find a system that can deliver volume to match. Of course you could store the water produced but the longer it’s stored, the more chance there is of it becoming contaminated once more. It may be wise to future-proof your lab by buying a system that slightly exceeds your current requirements, allowing you to cope if your demand for pure water increases in the months ahead.

The quality of your feed water supply can significantly affect the system you require. Whether you use mains water or a central supply it’s possible that regular checks for contamination are not carried out. A lab system that monitors purity can be of great help to improve consistency in regular procedures and to prevent long term degradation in results (e.g. baseline drift in HPLC).

Most systems will be classified by the type of water produced so it is important to think about your specific applications, and any future applications, before choosing the most suitable water type. You will find that purification technologies are available in combination on many systems, and therefore it is paramount to choose a system which has the right combination for your applications.

Systems can offer a range of daily outputs of up to 2000 liters or more (some will list their output per hour rather than per day) so both daily water and instant requirements need to be considered. A flexible output could be important for labs with variable demands in terms of water volume and application.

If you are putting together a tender, consultation with a range of manufacturers would be important to ensure the tender does not exclude systems that would be otherwise optimal for your needs.

Once you have the right system, regular, preventative maintenance is very important. New systems may have built-in alarms and calibrators that warn if certain components are coming to the end of their lives. They may be capable of testing the water routinely to make sure that it continues to remove the impurities that will interfere with your analysis. The level of monitoring can be set depending on your working style from daily, weekly or even monthly. Depending on your budget some manufacturers will offer aftercare maintenance as part of their deal or be able to advise on what you can do for yourself. Whatever system you choose make sure the water is circulated regularly as moving water stays purer for longer especially when considering biological impurities.

To help you choose the correct system, use the SelectScience product and supplier directory for an overview of systems from leading manufacturers and read user reviews from other SelectScience members.