24 Issue 1 2021
water analysis, purification & testing
The impact of inorganic compounds W
hat are common inorganic impurities in purified water? The most common inorganic impurities in purified water are residuals of the more common ions in feed water – sodium, calcium, iron, magnesium, chloride, sulphate, nitrate – and ions weakly held on ion-exchange resin – silicates and borates. Bicarbonate ions will usually be present, as well, produced by the dissolution of atmospheric CO2 in the product water on exposure to the environment. Where do inorganic impurities come from? Inorganic ions are the most abundant of the impurities in the feed water used to supply water purification systems. These can carry over into the product purified water if they are not removed effectively. They can also be released from ion-exchange (IX) media within the purification system as the media IX capacities are used up.
the lowest levels of impurities but, due to the slight ionisation of water into hydrogen and hydroxyl ions, even with 18.2MΩ.cm resistivity water, ppb levels of impurity ions may be present. The absence of trace ions can only be assured by carrying out regular specific analyses, notably by ICP-MS, or using a water-purification system design which guarantees their removal, such as PureSure. What levels are important? The significance of impurities depends on the application. For ultra-trace analysis even very low (sub-ppb) levels of inorganic ions can interfere significantly. Type 1+ water with a resistivity of 18.2MΩ.cm is essential. For less sensitive analyses higher impurity levels may be acceptable (Type 2+ or 2 with resistivity respectively of 10 or 1MΩ.cm). How does Elga remove inorganic impurities? In Elga systems typically over 95% of ions
are removed by high-rejection reverse osmosis membranes. A subsequent storage reservoir is protected by CO2removing vent-filtration. The remaining ions are removed by recirculation through ionexchange cartridges. The purest, high-efficiency mixed bed resins are used throughout. The use of PureSure - twin ion-exchange packs with resistivity monitoring both between the packs and in the product water – ensures that the purification packs are exchanged before there is any chance of the second pack becoming less than 100% effective. This guarantees the minimum levels of impurity ions are achieved and maintained. The IX capacity is also maximised. Applications • Microbiology • Liquid Chromatography (LC) • Electrochemistry • ICP-MS and ICP-OES • Immunochemistry
The major impurity in water is inorganic compounds
Water purification technologies • Ion exchange • Reverse osmosis • PureSure. Credit: Elga Veolia – The full article can be viewed here: https://bit.ly/2Y6YnFh. Elga products are available from Labotec in South Africa. LABOTEC (PTY) LTD JHB: (011) 315 5434 CPT: (021) 531 7660 DBN: (031) 566 4870 Fax: (011) 315 5882 sales@labotec.co.za www.labotec.co.za
What applications do inorganic impurities affect? Clearly, the presence of an impurity containing an element being determined will directly affect the accuracy of the results of elemental analysis. Other elements/compounds with overlapping spectral emissions or isotopic masses will also interfere with ICP-OES and ICPMS analyses respectively. Higher concentrations of less soluble species can lead to degradation in spray characteristics for these techniques and AAS and can degrade column and detector performance in HPLC. Impurity ions can also affect ionisation and form multi-atom ions in ICP-MS and LC-MS. How are inorganic impurities monitored? The universal method of monitoring for ionic impurities in purified water is by measuring its electrical conductivity/ resistivity. A resistivity of 18.2MΩ.cm is essential for ultrapure water containing
PureSure technology is used in the PureLab Chorus 1 which features a unique double purification pack and monitoring system
Eco IC – The very best of ion chromatography available for everybody
T
he Metrohm Eco IC was developed so that everybody is able to benefit from the power of ion chromatography. Focusing on the essentials, this new instrument provides the very best of ion chromatography at a very affordable price. Stripped of the ‘bells and whistles’ of sophisticated high-end instrumentation, the Eco
IC enables straightforward and robust analysis of anions, cations, and polar substances. The Eco IC is the preferred solution for users who: • do routine water analysis and need a dedicated solution • teach ion chromatography in higher education and depend on a simple and robust instrument • prefer an entry-level instrument at an affordable price, which they can upgrade any time to automate their analyses. The Eco IC makes these users happy with features that matter most to them, such as: • Intuitive, convenient software (MagIC Net) to control their instrument
• Smart system monitoring to safeguard robust operation and reproducible results • Readily available system automation for up to 36 samples • Exceptional Swiss quality backed by unique warranties • Proficient on-site service and support by a global team, who speak their native tongue. METROHM SA (PTY) LTD Tel: (011) 656 1918 CPT: (021) 852 0213 DBN: (031) 265 0067 Fax: (011) 656 2698 076 643 7113 info@metrohm.co.za www.metrohm.co.za
