Photometric Determination of Aluminium (Total) in Limestone with Chromazurole S After Fusion Melting

Abstract

This protocol outlines the photometric determination of aluminium levels in limestone using Spectroquant^® test kits. Following sample preparation by fusion melting, the procedure utilizes a spectrophotometer to measure the aluminum content, ensuring precise results. 

Section Overview:

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

Introduction

Monitoring aluminium content in limestone is crucial for ensuring the quality and performance of materials used in various construction applications. Aluminium can directly influence the reactivity of limestone in cement production, thus impacting the setting and hardening of concrete. It also plays a pivotal role in affecting the durability and strength of limestone-based construction materials.¹

Common determination methods for aluminium in limestone include photometric analysis, Inductively coupled plasma (ICP) spectroscopy, and X-ray fluorescence (XRF).² Photometric determination is preferred due to its high sensitivity, rapid analysis, cost-effectiveness, and user-friendly process. It is the method of choice for accurate and efficient analysis of aluminium content in limestone, particularly in the construction industry.

Experimental

This application note describes the sample preparation for total aluminum in limestone before the photometric determination of aluminium using the Spectroquant^® Aluminium Cell Test (1.00594), or the Spectroquant^® Aluminium Test (1.14825).

With the Spectroquant^® Aluminium Tests, the aluminum 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 thermal decomposition of limestone in the presence of sodium hydroxide initiates a series of chemical transformations. Upon heating, limestone decomposes to form calcium oxide and carbon dioxide. The produced calcium oxide subsequently reacts with sodium hydroxide to yield soluble calcium hydroxide. This reaction enhances the solubility of calcium in an aqueous environment, resulting in a saturated limewater solution. Adjusting the pH with hydrochloric acid to a value of 3-4 stabilizes ions in solution, preventing precipitation as carbonate.^3,4

The overall process effectively transforms limestone into a water-soluble form, suitable for subsequent analytical applications. This methodology is critical for the photometric analysis of aluminium in limestone samples.

After the sample preparation, the aluminium ions react in a weakly acidic, acetate-buffered solution with chromazurol S to form a blue-violet compound that is determined photometrically. Due to the intrinsic orange coloration of the reagent blank, the measurement solution is orange-red to red in color.

The method is analogous to APHA 3500-Al B and DIN ISO 10566 E30.

Measuring Ranges, Test Kits and Method Numbers

Expected content in the original sample (measuring range of related test kit)	Cell	Instruments	Method No.	Test kit
0.004 – 0.040% Al (0.020 – 0.200 mg/L Al)	50 mm rectangular cell	Prove1) 100/300/600 plus, Nova 60A	43	1.14825
0.01 – 0.12% Al (0.05 – 0.60 mg/L Al)	20 mm rectangular cell	Prove1) 100/300/600 plus, Nova 60A
0.02 – 0.24% Al (0.10 – 1.20 mg/L Al)	10 mm rectangular cell	Prove1) 100/300/600 plus, Nova 60A
0.004 – 0.01% Al (0.02 – 0.50 mg/L Al)	16 mm round cell	Prove1) 100/300/600 plus, Nova 60A	196	1.00594
0.004 – 0.140% Al (20 - 700 μg/L Al)	16 mm round cell	Move 100	20	1.14825
0.01 – 0.10% Al (0.05 - 0.50 mg/L Al)	24 mm round cell	Move 100	21	1.00594
1)Also, legacy systems Spectroquant® Prove 600/300/100 are compatible and preprogrammed with these methods.

Applicable Sample

• Limestone

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 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, the following is necessary:

• Analytical balance
• Nickel crucible
• Hydrochloric acid fuming 37%, for analysis EMSURE^® ACS,ISO, Reag. Ph Eur (1.00317)
• Bunsen burner
• Glass beaker
• Water for analysis EMSURE^® (1.16754)
• Sodium hydroxide pellets for analysis EMSURE^® (1.06498)
• 200-mL volumetric flask
• Paper filter
• Universal Indicator strips pH 0 – 14 (1.09535)

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

• Spectroquant^® Aluminium Cell Test (1.00594)
• Spectroquant^® Aluminium Test (1.14825)

Instruments

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^® Aluminium Test (1.14825)

• Rectangular cells 10 mm (1.14946) and/or
• Rectangular cells 20 mm (1.14947) and/or
• Rectangular cells 50 mm (1.14944) and/or
• Semi-microcells 50 mm (1.73502)

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

• In a nickel crucible, mix about 100 mg of powdered sample material with 8 pellets of sodium hydroxide (1.5 g).
• Heat the covered crucible with a gas burner for 30 min to weak redness.
• After cooling, dissolve the content of the crucible in water. For this purpose, put the crucible with the cover into a beaker and heat with 30 - 50 ml water for analysis on the water bath, until the molten mass has dissolved. Ultra sonification accelerates the dissolution.
• Adjust the solution with hydrochloric acid 37% to a pH value of 3 - 4, transfer quantitatively into a 200-ml volumetric flask, fill up to volume with water for analysis and mix well.

Photometric Analysis

This prepared sample can be analyzed with following test kits:

• Spectroquant^® Aluminium Cell Test (1.00594)
• Spectroquant^® Aluminium Test (1.14825)

Follow 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 instructions given in the instrument manual and package inserts.

Calculation

The obtained result read off in mg/L Al must be converted as follows:

                            Aluminium (total) content in % = analysis value in mg/L Al x 0.02

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, aluminium standard solutions or Spectroquant^® CombiCheck 100 can be used.

Besides a standard solution with 0.40 mg/L Al, CombiCheck 100 also contains an addition solution for determining sample-dependent interferences (matrix effects).

For details on how to perform the AQA check see the instrument-specific manuals.

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.

References

1. Puerta‐Falla G, Balonis M, Le Saout G, Falzone G, Zhang C, Neithalath N, Sant G. 2015. Elucidating the Role of the Aluminous Source on Limestone Reactivity in Cementitious Materials. J. Am. Ceram. Soc. 98(12):4076-4089. https://doi.org/10.1111/jace.13806

2. Šiler P, Kolářová I, Bednárek J, Janča M, Musil P, Opravil T. 2018. The possibilities of analysis of limestone chemical composition. IOP Conf. Ser.: Mater. Sci. Eng. 379012033. https://doi.org/10.1088/1757-899x/379/1/012033

3. Brown TE, LeMay HE, Bursten BE, Murphy C, Woodward P, Stoltzfus ME. 2021. Chemistry: The Central Science. 15th edition. Pearson Education.

4. Miessler GL, Fischer PJ, Tarr DA. 2014. Inorganic Chemistry. 5th edition. Pearson.