Photometric Determination of Sulfate in Building Materials with Turbidimetric Method After Water Extraction/Fusion Melting

Abstract

This protocol outlines the photometric determination of Sulfate levels in building materials using Spectroquant^® test kits. Following a sample preparation by water extraction or fusion melting, the procedure utilizes a spectrophotometer to measure the sulfate content, ensuring precise results. 

Section Overview:

• Introduction
• Experimental
• Reagents, Instruments and Materials
• Analytical Procedure
• Calculation
• Analytical Quality Assurance
• References

Introduction

Sulfate can have a significant impact on the durability and stability of construction materials. Excess sulfate may lead to a chemical reaction with certain building materials, such as concrete, resulting in a phenomenon known as a sulfate attack. This can compromise structural integrity over time, leading to cracking, expansion, and deterioration. Hence, measuring and monitoring sulfate content in building materials is essential for ensuring the longevity and performance of structures. This is particularly important in environments where sulfate exposure is a concern, such as near coastal areas or in soil with high sulfate levels.¹

Common determination methods for analyzing sulfate in building material after appropriate sample preparation include Photometric Analysis, Gravimetric analysis², Titration methods², and Ion chromatography³. The photometric method offers distinct benefits, including high sensitivity, rapid analysis, cost-effectiveness, and a user-friendly process with minimal sample preparation. This makes it the preferred choice for accurate and efficient determination of sulfate content in building materials.

Experimental

This Application Note describes the sample preparation for Sulfate in building materials before the photometric determination of Sulfate using Spectroquant^® Sulfate Cell Tests (1.01812, 1.02532, 1.14548, 1.02537, 1.00617, 1.14564).

With the Spectroquant^® Sulfate Tests the sulfate content can be determined quickly and easily. The methods are preprogrammed on the corresponding Spectroquant^® photometers. Calibration is not necessary. All reagents required for the measurement are included in the test kits.

Method

The fusion melting process induces significant chemical transformations in the building material. When heated with sodium hydroxide, a strong base, the sulfate ions present in the material can undergo reactions that lead to the formation of soluble sodium sulfate. The high temperature promotes the breakdown of sulfate-containing compounds, facilitating the release of sulfate ions into the solution.

After the sample preparation the sulfate ions react with barium ions to form slightly soluble barium sulfate. The resulting turbidity is measured in the photometer (turbidimetric method).

The method is analogous to EPA 375.4, APHA 4500-SO42- E, and ASTM D516-16.

Applicable Sample

• Building materials

Influence of Foreign Substances

Foreign substances in the sample solution can

• increase the measurement value because of an amplification of the reaction
• lower the measurement value because by preventing the reaction

A quantification of these effects is stated in tabular form in the respective package inserts for the most important foreign ions and substances. The tolerance limits have been determined for the individual ions and substances; they may not be evaluated cumulatively.

In the case of samples with a complex, in many cases inexactly known composition (matrix) it is particularly difficult to estimate the potential influence of the foreign substances on the analysis (matrix effect). The following instructions describe a method by means of which the user can test whether a matrix effect is present or not.

• Interference check by dilution
• Interference check by spiking

Reagents, Instruments and Materials

Test/Reagents/Kit(s)

For the sample preparation, depending on the chosen procedure (see below) some or all of the following is necessary:

• Analytical balance
• 200-mL volumetric flask
• Muffle furnace
• Nickel crucible with nickel plate
• Sodium hydroxide pellets for analysis EMSURE^® (1.06498)
• Water for analysis EMSURE^® (1.16754)
• Nitric acid 65%, for analysis EMSURE^® Reag. Ph Eur, ISO (1.00456)
• 100-mL volumetric flask
• Paper filter
• Universal Indicator strips pH 0 – 14 (1.09535)

If necessary, required for pH adjustment:

• Sodium hydroxide solution 1 mol/l Titripur^® (1.09137)
• Sulfuric acid 0.5 mol/l Titripur^® (1.09072)

For the measurement, one of the following Spectroquant^® test kits is necessary:

• Spectroquant^® Sulfate Cell Tests (1.02532, 1.14548, 1.02537, 1.00617, 1.14564)
• Spectroquant^® Sulfate Tests (1.01812)

For the measurement, one of the following Spectroquant^® photometers is necessary:

• Spectroquant^® UV/VIS Spectrophotometer Prove 600 plus (1.73028)
• Spectroquant^® UV/VIS Spectrophotometer Prove 300 plus (1.73027)
• Spectroquant^® VIS Spectrophotometer Prove 100 plus (1.73026)
• Spectroquant^® Colorimeter Move 100 (1.73632)

Also, legacy systems are suitable:

• Spectroquant^® Spectrophotometer Prove 600/300/100
• Spectroquant^® Photometer NOVA 60A

Instrument Accessories

Rectangular cells are necessary for Spectroquant^® Sulfate Test (1.01812)

• Rectangular cells 10 mm (1.14946) and/or
• Rectangular cells 20 mm (1.14947) and/or
• Rectangular cells 50 mm (1.14944) 

Software for Data transfer (optional)

The Spectroquant^® Prove Connect to LIMS software package provides an easy way to transfer your data into a preexisting LIMS system.

• Prove Connect to LIMS (Y.11086)

Analytical Procedure

Sample Preparation

Differential analysis of sulfate soluble in hot water and total sulfate can be carried out with suitable sample preparation.

Sample preparation - hot water extraction:

• Prepare a fine powder of the sample and dry at 105 °C.
• Mix 5 g with water for analysis and boil for 30 minutes on a hot plate.
• Allow to cool, transfer the suspension to a 200-mL volumetric flask, and make up to the mark with water for analysis.
• Mix well, filter through a paper filter, and then use as a sample for the determination of water – soluble sulfate.

Sample preparation - total content:

• Mix 100 mg of the finely powdered material along with 10 pellets of sodium hydroxide, place in a nickel crucible, and heat for 30 minutes at 550 °C in a muffle furnace.
• Allow to cool and carefully add 10 mL of water for analysis.
• If necessary, heat gently to obtain a suspension.
• Adjust to approx. pH 5 with nitric acid.
• Using water for analysis, transfer the suspension to a 100-mL volumetric flask, make up to the mark with water for analysis and mix well.
• Filter through a paper filter before carrying out the analysis.

Photometric Analysis

This prepared sample can be analyzed with the following test kits:

• Spectroquant^® Sulfate Tests (1.01812)
• Spectroquant^® Sulfate Cell Test (1.02532)
• Spectroquant^® Sulfate Cell Test (1.14548)
• Spectroquant^® Sulfate Cell Test (1.02537)
• Spectroquant^® Sulfate Cell Test (1.00617)
• Spectroquant^® Sulfate Cell Test (1.14564)

Follow the instructions given in the package inserts or instrument manual.

Notes on measurement

If the prepared sample is colored, perform a sample blank before the measurement of the sample itself. This step is necessary to compensate for the intrinsic color.

Follow the instructions given in the instrument manual and package inserts.

Calculation

The obtained result read off in mg/L SO₄^2- must be converted as follows:

                      Sulfate (water-soluble) content in % = analysis value in mg/L SO₄^2- x 0.004

                      Sulfate (total) content in % = analysis value in mg/L SO₄^2- x 0.1

Analytical quality assurance

Analytical quality assurance (AQA) is recommended before each measurement series.

To check the photometric measurement system (test reagent, measurement device, handling) and the mode of working, sulfate standard solutions or Spectroquant^® CombiCheck kits can be used. Besides standard solutions, CombiCheck also contains an additional solution for determining sample-dependent interferences (matrix effects).

A certificate of analysis is provided for each batch and can be downloaded online on the product page of the test as well as a certificate of quality, where all batches are considered. In the certificates, the performance characteristics determined in accordance with ISO 8466-2 and DIN 38402 A51 are given.

Nevertheless, it is recommended to determine the performance characteristic yourself so that all specific factors that may impact the performance (test reagents, measurement device, handling) are considered in the characteristic data.