ION CHROMATOGRAPHY OF WATER-SOLUBLE IONS IN CONCRETE
Ion chromatography (IC) as an analytical technique has seen an enormous surge in popularity, due partly to the simplicity of many of the methods as well as other factors such as market forces driving down the expenditure costs of the equipment and an improved instrument power.
The use of IC as a potential method for the analysis of water-soluble anions (e.g., chloride, sulphate, nitrate, nitrite, bromide, and fluoride) and cations (e.g., lithium, calcium, sodium, potassium, ammonium) in concrete presents an excellent alternative to the conventional gravimetric methods that are widely used. Appropriate chromatography columns and eluents are used for analyses of water-soluble anions and cations in concrete.
Ion chromatography is a precise, durable technique that allows the user the functionality of quick analysis turnaround once the samples are in an ionic, homogenous form. Only a very small amount of sample is required for the analysis and the quantified results obtained within a matter of minutes.
Usually, approximately 1 gram of pulverized concrete or mortar sample (finer than 0.3 mm) is digested in 50 ml deionized water first by rapidly boiling on a magnetic stirrer for 10 to 15 minutes followed by 24 hour digestion in ambient laboratory temperature with intermittent stirring. The digested sample is then filtered under vacuum through two 0.2-micron filter paper to collect the filtrate containing water-soluble ions of interest. The filtrate is diluted to a final volume of 200 ml, a 10 ml aliquot of which is then loaded to the Metrohm autosampler to run with a Metrohm ion chromatography unit.
Procedure of ion chromatography of anions in water are described in ASTM D 4327.
Multiple samples can be loaded in a 148-position autosampler to run overnight or during the day freeing the user to perform other duties. The running costs of ion chromatography with Metrohm instruments are surprisingly low, requiring only the acquisition of chemicals required for the eluent and suppressor module as well as a clean, reliable source of deionized water. Ion chromatography is a clean technique as all the reagents are enclosed; its robustness and reliability are assured, demonstrating precisely the reason why it is rapidly becoming the method of choice for many analysts in a wide range of different industries.
ION CHROMATOGRAPHY OF WATER-SOLUBLE ANIONS
Metrohm 881 Compact IC Professional & 858 Professional Sample Processor
Water-soluble anions (fluoride, chloride, bromide, nitrite, nitrate, phosphate, and sulfate) in cement, concrete, and mortar samples are determined by Metrohm 881 Compact IC Pro with attached 858 Professional Sample Processor. The 881 Compact IC Pro is an intelligent ion chromatograph of compact design with column oven for the determination of anions or polar substances with sequential suppression. It can be operated with various types of detection. The 858 Professional Sample Processor processes samples from 500 µL to 500 ml. The sample transfer takes place either by means of a peristaltic pump on the 850 Professional IC system or with an 800 Dosino.
IN-VIAL AUTO DILUTION OF FILTRATES
Metrohm 881 Compact IC Professional & 858 Professional Sample Processor
Metrohm's MagIC Net software running 881 Compact IC and 858 Professional Sample Processor can do automated in-vial dilution of filtrates of water-digested concrete samples if concentrations detected in the original sample filtrate exceeds calibration range of standards, thus minimizing additional sample dilution. Additionally, standards for calibrations can be prepared from a concentrated multi-anion standard by setting different dilution factors.
ION CHROMATOGRAPHY OF WATER-SOLUBLE CATIONS
Metrohm 861 Advanced Compact IC & 788 IC Sample Processor
Water-soluble cations (lithium, ammonium, sodium, potassium, calcium, and magnesium) in cement, concrete, and mortar samples are determined by Metrohm 861 Advanced Compact IC. Advanced Compact IC is suited for applications without suppression such as cation and non-suppressed anion determinations as well as for methods combining conductivity with other types of detection. Metrohm’s 861 Advanced Compact IC with sequential suppression attached to a 788 IC Filtration Sample Processor can run 127 samples unattended. With values below 1 µS/cm after suppression, the background conductivity approaches the theoretical limit of 0.05 µS/cm. When running anions, low background conductivity directly relates to very low detection limits, which means the compact ion chromatograph now covers the single-figure ppb range. In short: No injection peak, No system peak, No interference from carbonate, Previously unachieved precision for rapidly eluting anions, Significantly improved detection limits, Sequential suppression, Flexibility of carbonate eluents with the baseline of a hydroxide eluent. 861 Advanced Compact IC provides larger peak areas, no injection peak, no carbonate peak, and superior baseline stability, and compact footprint, plus <2 ppb detection sensitivity for standard anions, measuring range expanded to 5000 µS/cm, column heating, analog and digital output, no gas supply or computer plug-in cards.
SEQUENTIAL SUPPRESSION
The 861 Advanced Compact IC combines the two most effective suppression techniques sequentially into a single instrument: namely, the second generation of the Metrohm Suppressor Module «MSM II» for chemical suppression, which coincides with a completely new development – the 853 Metrohm CO2 Suppressor. This combination guarantees an accurate and reproducible analysis in ion chromatography. The removal of CO2 keeps the carbonate equilibrium from affecting the peak areas: with sample concentration and sample volume being the same, up to 50% larger peak areas and markedly lower detection limits are obtained. No carbonate peak – this means no bothersome interferences during the quantification of certain analyte anions. For example, on many polystyrene/divinylbenzene columns, chloride and carbonate coelute. The use of the CO2 suppressor eliminates this problem. The virtual absence of an injection peak improves the determination of rapidly eluting anions such as fluoride. Although excellent separation between the injection peak and fluoride peak is achieved on polyalcohol columns, the use of the CO2 suppressor improves the detection limit even further. As the injection peak is negligibly small, considerably larger sample volumes can be injected.
CMC has Metrohm’s 861 Advanced Compact IC with sequential suppression attached to a 788 IC Filtration Sample Processor that can run 127 samples unattended. With values below 1 µS/cm after suppression, the background conductivity approaches the theoretical limit of 0.05 µS/cm. When running anions, low background conductivity directly relates to very low detection limits, which means the compact ion chromatograph now covers the single-figure ppb range. In short: No injection peak, No system peak, No interference from carbonate, Previously unachieved precision for rapidly eluting anions, Significantly improved detection limits, Sequential suppression, Flexibility of carbonate eluents with the baseline of a hydroxide eluent. 861 Advanced Compact IC provides larger peak areas, no injection peak, no carbonate peak, and superior baseline stability, and compact footprint, plus <2 ppb detection sensitivity for standard anions, measuring range expanded to 5000 µS/cm, column heating, analog and digital output, no gas supply or computer plug-in cards.
CHROMATOGRAM OF A 10-PPM STANDARD SOLUTION OF 7 ANIONS RUN IN CMC'S 861 ADVANCED COMPACT IC WITH ATTACHED 788 SAMPLE PROCESSOR
WATER-SOLUBLE CATIONS IN CONCRETE & MASONRY
Profiles of Lithium, Ammonium, Sodium, Potassium, Calcium, and Magnesium Ions
APPLICATIONS
Migration of alkalis through a concrete slab
Floor covering failure from alkalis
Lithium salts applied to a concrete slab affected by alkali-silica reactions
Ammonium salts in deicing chemicals
Sodium chloride vs. Calcium chloride based deicer applied on a concrete surface
WATER-SOLUBLE ANIONS IN CONCRETE & MASONRY
Profiles of Fluoride, Chloride, Bromide, Nitrite, Nitrate, Phosphate, and Sulfate Ions
APPLICATIONS
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Detection of chloride-based deicers on concrete surface
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Chloride-based set accelerating admixture in concrete
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External sulfate attack in concrete
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Internal sulfate attack in concrete
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Wastewater contamination in concrete tank
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Chemical profiles in PCCP
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Salt contamination
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Concrete and Masonry in Marine Environments
A CASE STUDY ON APPLICATION OF ION CHROMATOGRAPHY IN CONCRETE DISTRESS
Sulfates released from oxidation of pyrrhotite in unsound aggregates in a concrete
ACCELERATED OXIDATION TEST OF AGGREGATES EXTRACTED FROM CONCRETE
Internal Sulfate Attack in A Concrete Foundation
Sulfates released from pyrrhotite-bearing crushed gneiss coarse aggregate particles in a residential concrete foundation has caused internal sulfate attacks and associated cracking. Aggregates extracted from distressed concrete are crushed in a strong oxidant (35% hydrogen peroxide solution) to release sulfates. Filtrates are then measured by ion chromatography to determine sulfate contents after various days of immersion.
DETERMINATION OF WATER-SOLUBLE CHLORIDE & SULFATE CONTENTS IN CONCRETE BY POTENTIOMETRIC TITRATION, ION CHROMATOGRAPHY, AND X-RAY FLUORESCENCE
An ongoing research in CMC's Chemical Laboratory
Determining chloride and sulfate contents in concrete by three independent methods from potentiometric titration to XRF and IC showed good correlation of results amongst the methods. Compared to titration, IC provided not only water-soluble chloride and sulfate contents but also concentrations of other anions from fluoride, through bromide, nitrate, nitrite, and phosphate some of which may have relevance to concrete exposed to special environments (e.g., fluoride content for concrete containment tanks exposed to hydrofluoric acid solutions).
Areas where IC has promising applications in concrete include (i) evaluating potential roles of chloride-containing deicing chemicals in concrete surface distress, (ii) chloride-induced corrosion of steel in concrete, (iii) potential source of sulfates in external or internal sulfate attacks in concrete, (iv) depths of contamination of concrete with water-soluble ions in wastewater containment tanks, and (v) presence of nitrate-based corrosion inhibitor in concrete.
