Technical Field

The present disclosure relates generally to a method and composition for determining a quantity of magnesium ions present in a mixture, solution, or a sample. More specifically, the present disclosure relates to the use of sulfide ions for precipitating metal ions to thereby facilitate or enable a more accurate quantification of magnesium ions present in a mixture, solution, or sample, such as a latex sample.

Background

Typically, latex (e.g., field latex and concentrated latex) manufacturers have to characterize latex properties. Latex manufacturers are often required to provide the specifications of their products (i.e., latex) to their buyers (e.g., manufacturers of rubber products). One important property or characteristic of latex that is commonly reported or included in the specifications of latex is the magnesium ion content or concentration, which is usually represented in ppm level. The presence of magnesium ions in latex (e.g., field latex and concentrated latex) adversely affects the mechanical stability of said latex. More specifically, an increase in the magnesium ion content in latex results in an undesirable decrease in the Mechanical Stability Time (MST) of latex.

In general, the MST value of latex is expressed as the number of seconds elapsed from a start point of a mechanical stability test to an end point of said mechanical stability test. The end point of the test is generally determined by the first appearance of small pieces of coagulated rubber. The formation of coagulated rubber is due to binding between magnesium ions and insoluble long-chain fatty acid soaps or salts present in latex. The coagulated rubber decreases the MST value of latex. Therefore, the magnesium content in latex (e.g., field latex and concentrated latex) generally has to be accurately determined and reported to latex buyers or users, for aiding more appropriately adjusted or conditioned downstream processes in the manufacturing of rubber products. Currently, techniques available for quantifying the amount or concentration magnesium or magnesium ions present within a latex sample include complexometric titration between metals using ethylene diamine tetraacetic acid (EDTA) as a titrant. The quantity (e.g.,. volume) of known concentration EDTA consumed during the titration is measured, and this quantity of EDTA can provide a reflection of the amount or concentration of magnesium ions present in the latex sample.

However, EDTA does not selectively react with magnesium ions. Instead, EDTA also reacts with other interfering metal ions (e.g., transition metal ions) that may be present in a latex sample. Accordingly, the quantity (i.e., volume) of EDTA consumed during the titration will be a reflection of both the quantity of magnesium ions and the quantity of other interfering metals or interfering metal ions. This results in positive errors in quantification of magnesium ions or an inaccuracy in the quantification of magnesium ions.

To circumvent, or prevent, non-specific reactions between EDTA and other interfering metal ions, cyanide ions, for instance in the form of potassium cyanide (KCN) or sodium cyanide (NaCN), have been used to mask or precipitate said interfering metal ions. Cyanide ions can generally bind to the interfering metal ions with strong bonds (i.e., high binding affinity), thereby leaving EDTA to react only with the magnesium or magnesium ions in a latex sample. Accordingly, the use of cyanide ions can enable an increased accuracy in the quantification of magnesium ions in a latex sample. However, cyanide is a generally considered to be a very toxic substance. According to the material safety data sheet (MSDS) of KCN, KCN is classified as "very toxic" and may be fatal if inhaled, swallowed, or absorbed through the skin. Moreover, KCN is said to be extremely destructive of mucous membranes and is a causation of burns when brought into contact with the skin. In view of conducting day-to-day quantitative determination of magnesium ions in large quantities of latex samples, techniques and methods requiring the use of cyanide ions, compounds, or substances may be considered to be unsuitable and undesirable, particularly in aspects of health and safety. Accordingly, a need exists for improved or alternative compositions, methods, and/or processes for accurately quantifying magnesium ions in a latex sample (e.g., field latex or concentrated latex sample).

Summary In accordance with a first embodiment of the present disclosure, there is disclosed a method that includes providing a latex mixture that includes magnesium ions and at least one different metal ion. The method also includes introducing sulfide ions to the latex mixture to provide a concentration of sulfide ions at least approximately 0.1 mM in the latex mixture for selectively precipitating at least a portion of the at least one different metal ion, and adjusting a pH value of the latex mixture to a value of higher than approximately 9.0. The at least one different metal ion have a higher binding affinity to the sulfide ions as compared to the magnesium ions.

In accordance with a second embodiment of the present disclosure, there is disclosed a method for quantifying magnesium ions in a latex sample including providing a latex sample that includes magnesium ions and transition metal ions comprising at least one of zinc, copper, and manganese ions. The method also includes adding a sulfide solution to the latex sample in at least one of a controlled, precise, and drop-wise manner to provide a concentration of sulfide ions at least approximately 0.1 mM, for instance, at least approximately 0.5mM, in the latex mixture for selectively precipitating at least a portion of the transition metal ions. The method also includes titrating the latex sample using EDTA as a titrant in a complexometric titration process and determining a quantity of EDTA that reacted in the complexometric titration process to thereby quantity magnesium ions present in the latex sample.

In accordance with a third embodiment of the present disclosure, there is disclosed a method for quantifying magnesium ions including providing a latex sample that includes magnesium ions and transition metal ions comprising at least one of zinc, copper, and manganese ions, and adjusting the latex sample to a pH of at least approximately 9.0, for instance, at least approximately 10.0. The method further includes adding sulfide ions to the latex sample to provide a concentration of sulfide ions at least approximately 0.1 mM in the latex sample. The sulfide ions selectively precipitates at least a portion of the transition metal ions to thereby one of facilitate and effectuate an increased accuracy in quantifying magnesium ions present in the latex sample.

In accordance with a fourth embodiment of the present disclosure, there is disclosed a kit for facilitating quantification of magnesium ions in a latex sample that comprises magnesium ions and transition metal ions comprising at least one of zinc, copper, and manganese ions. The kit includes a volume of sulfide solution to provide a concentration of sulfide ions of at least approximately 0.1 mM, for instance, at least approximately 0.5mM, to the latex sample. The kit also includes an alkaline solution including a mixture of sodium hydroxide and borax to one of facilitate and effectuate an increase in pH of the latex sample to at least approximately 9.0, for instance, at least approximately 10.0. When the sulfide ions is added to the latex sample, the sulfide ions selectively precipitates at least a portion of the transition metal ions in the latex sample to thereby one of facilitate and effectuate an increased accuracy in quantifying magnesium ions present in the latex sample.

Brief Description of the Figures Embodiments of the present disclosure are described hereinafter with reference to the figures in which:

FIG. 1 is a flowchart of a process for quantifying magnesium ions in a latex sample according to an embodiment of the present disclosure;

FIG. 2 shows the quantity of EDTA consumed during a titration process with each of a magnesium sample and a zinc sample in accordance with experiments conducted in association with an embodiment of the present disclosure;

FIG. 3 shows magnesium ion concentrations in different latex samples as determined in experiments conducted in accordance with an embodiment of the present disclosure;

FIG. 4 shows the results obtained in an experiment conducted to show the effect of using different methods, processes, or techniques for introducing sulfide ions to latex samples in accordance with an embodiment of the present disclosure; and FIG. 5 shows the results obtained in an experiment conducted to show the relative effectiveness of oxalate ions and cyanide ions in precipitating calcium ions in accordance with an embodiment of the present disclosure.

Detailed Description Latex manufacturers or sellers are typically required to determine the quantity of magnesium or magnesium ions present in their products, more specifically latex (e.g., field latex and concentrated latex). A common method of quantifying magnesium ions in a mixture, solution, or sample (e.g., latex sample) is via a complexometric titration process using ethylene diamine tetraacetic acid (EDTA) as a titrant. However, EDTA is also able to bind to other metal ions beside magnesium ions, for instance transition metals such as zinc, copper, and manganese ions. Accordingly, metal ions besides magnesium ions generally need to be first masked, precipitated, or removed, to thereby facilitate or effectuate an accurate quantification of magnesium ions present in a mixture, solution, or sample (e.g., latex sample). Embodiments of the present disclosure relate to compositions, methods, processes, and/or techniques for quantifying magnesium ions present in a mixture, solution, or sample. More specifically, embodiments of the present disclosure relate to use of sulfide ions for precipitating potentially interfering substances or metal ions present in a mixture or sample such that a subsequent quantification of magnesium ions in said mixture, solution or sample, for instance via a complexometric titration process with the use of EDTA as a titrant, can performed with a higher accuracy. Compositions, methods, processes, and/or techniques of many embodiments of the present disclosure address at least one issue, problem, or disadvantage that is associated with conventional methods, processes, or compositions for quantifying magnesium ions. The sulfide ions can be provided by, or derived from, ammonium sulfide. Alternatively, the sulfide ions can be provided by, or derived from, sodium sulfide or calcium sulfide. Other sources of sulfide ions can also be used. Although sulfide ions are disclosed herein for precipitating potentially interfering substances or metal ions present in a mixture or sample, other non-toxic substances, compositions, or compounds may also be used simultaneously with, or in substitution of, sulfide ions. For purposes of the present disclosure, a mixture, solution, or sample can be taken to be, and will hereinafter be referred to as, a latex sample or a latex mixture. However, a mixture, solution, or sample can also include other types of mixtures, solutions, and/or compositions (e.g., a natural extract or composition, a plant latex, a wastewater sample, or a chemical composition) within the scope of the present disclosure. In addition, values (e.g., volumes and concentrations) indicated in association with various embodiments of the present disclosure can be approximate values.

Brief Overview of Latex

Latex is commonly defined to be a stable dispersion or emulsion of polymer micro-particles in an aqueous medium. In nature, latex is typically a milky sap-like fluid that is found in approximately 10% of all flowering plants (or angiosperms). Plant cells or tissues in which latex is found make up the laticiferous system of the plant. Natural latex is a complex emulsion or mixture including proteins, alkaloids, starched, sugars, oils, tannins, resins, and gums that coagulates on exposure to air. Field Latex

Field latex generally refers to the raw form of latex harvested from latex producing plants that has not yet undergone further (or downstream) processing, refining, or concentrating processes. Field latex from plants, for example rubber (Hevea brasiliensis) plants or trees can be obtained by tapping. Concentrated Latex

Concentrated latex is a form of processed latex, which is obtained after a processing of field latex. Concentrated latex is considered to be a pure and clean raw material with a wide range of applications. Generally, there are two main methods of processing latex to obtain concentrated latex, namely concentration by creaming and concentration by centrifugation. Generally, concentration by creaming involves mixing of a creaming agent such as ammonium alginate or tamarind seed powder with field latex and allowing the field latex to separate into two layers, which are an upper layer of concentrated latex and a lower layer of serum containing very little rubber. The lower layer of serum is removed, leaving the concentrated latex having about 50-55% DRC (dry rubber content). Generally, concentration by centrifugation involves separation of field latex into two fractions by centrifugation. One fraction contains the concentrated latex of more than 60% dry rubber and the other fraction contains approximately 4% to 8% dry rubber (skim latex).

Processes for Quantifying Magnesium Ions in a Latex Sample Many embodiments of the present disclosure relate to processes for quantifying magnesium ions in a latex sample.

FIG. 1 shows a flowchart of a process 100 for quantifying magnesium ions in a latex sample according to an embodiment of the present disclosure.

In a first process portion 110, a known volume of a latex sample is provided. In many embodiments of the present disclosure, the latex sample is at an alkaline pH. In numerous embodiments, the latex sample is at a pH of at least approximately 9.0, and more preferably at least approximately 10.0. In several embodiments, an alkaline solution is used, for instance mixed, with the latex sample to adjust and/or maintain the pH of the latex sample.

In numerous embodiments, the alkaline solution can include sodium hydroxide. In several embodiments, the alkaline solution can include sodium hydroxide and borax. In particular embodiments, the volume or concentration of sodium hydroxide to borax in the alkaline solution can be selected and/or varied, for instance to achieve a particular latex characteristic or property. In various embodiments, the alkaline solution functions as a buffer solution.

In some embodiments, the alkaline solution has a borax concentration of at least approximately 0.05M and a sodium hydroxide concentration of at least approximately 0.2M. In particular embodiments, the alkaline solution has a borax concentration of at least approximately 0.10M, for example approximately 0.133M, and a sodium hydroxide concentration of at least approximately 0.30M, for example approximately 0.333M.

Latex samples often include other metal ions or metal compounds, for instance zinc ions, copper ions, and manganese ions, besides magnesium ions. Accordingly, to selectively quantify magnesium ions, the other metal ions (which can be referred to as interfering metal ions) typically need to first masked, precipitated, and/or removed. In a second process portion 120, sulfide ions are added or introduced to the latex sample. More specifically, in many embodiments, a solution, mixture, or composition that includes sulfide ions (hereinafter referred to as a sulfide solution) is added to the latex sample. The sulfide solution is, for example, ammonium sulfide. In many embodiments, the volume and/or sulfide concentration of the sulfide solution can be selected and/or varied to provide, or obtain, a selected concentration of sulfide ions in the latex sample.

In numerous embodiments, sulfide ions are added to a latex sample such that the concentration of sulfide ions in the latex sample is at least approximately 0.1 mM. In several embodiments, sulfide ions are added to a latex sample such that the concentration of sulfide ions in the latex sample is at least approximately 1.OmM. In particular embodiments, sulfide ions are added to a latex sample such that the concentration of sulfide ions in the latex sample is at least approximately 2. OmM, for example approximately 2.5mM, 5. OmM, or more.

In many embodiments, the latex sample has an added concentration of sulfide ions of at least approximately 0.1 mM per 100 grams of latex sample. In numerous embodiments, following sulfide ion addition, the latex sample has a concentration of sulfide ions of at least approximately 0.5mM per 100 grams of latex sample. In several embodiments, the latex sample has a sulfide concentration of at least approximately 1.OmM per 100 grams of latex sample, for instance at least approximately 1.5mM, 2. OmM, or 2.5mM per 100 grams of latex sample.

In some embodiments, approximately 4.0 milliliters (mL) of a sulfide solution with approximately 0.6M of sulfide ions is added to a latex sample with approximately 10.0 gram of latex in order to achieve a concentration of approximately 2.4mM per 10.0 gram of latex. Alternatively, 8.0mL of a sulfide solution with 0.3M of sulfide ions is added to the latex sample with 10.0 gram of latex in order to achieve a concentration of approximately 2.4mM per 10.0 gram of latex.

In some embodiments, the amount (e.g., concentration) of sulfide ions provided to a particular latex sample is at least partially dependent upon the source of the latex sample and/or an expected quantity (e.g., concentration) of interfering metal ions present in the latex sample. In various embodiments, the concentration of sulfide ions provided to a particular latex sample is in excess of the concentration of the interfering metal ions present in the latex sample.

As mentioned above, in many embodiments, the latex sample has an alkaline pH, for example at least approximately 9.0, and more preferably at least approximately 10.0. The alkaline pH of the latex sample can facilitate or enhance precipitation of the interfering metal ions by the sulfide ions. In addition, the alkaline pH of the latex sample can also facilitate or enhance a reaction between EDTA and metal ions (e.g., alkaline earth metal ions), for instance magnesium and/or calcium ions.

In some embodiments, the latex sample is agitated, shaken, or blended during the addition of the sulfide solution thereto. The agitated, shaking, or blending of the latex sample during addition of the sulfide solution can enable a better interaction and/or reaction between the sulfide ions and the interfering metal ions.

A third process portion 130 involves selective precipitation or masking of interfering metal ions by the sulfide ions added to the latex sample. Selective precipitation of interfering metal ions / metal compounds

Generally, selective precipitation is a technique or process in which one ion (e.g., an interfering metal ion) is selectively removed from a mixture of different ions by precipitation. Typically an ion or a compound (referred to as a capture ion) with a higher binding affinity for the interfering metal ion is added to the mixture of different ions. The capture ion selectively or preferentially binds to the interfering metal ion to thereby facilitate precipitation and/or separation of said interfering metal ion.

In numerous embodiments of the present disclosure, the sulfide solution is added to the latex sample in a controlled or precise manner, for instance, a controlled multi-step pr incremental manner. In several embodiments, the sulfide solution is added to the latex sample in a drop- wise manner. In particular embodiments, a dispenser or a dropper is used to facilitate or effectuate the addition of the sulfide solution to the latex sample.

In various embodiments, the sulfide solution is added to the latex sample at a speed of between approximately 0.5 and 5 drops per second. In particular embodiments, the sulfide solution is added to the latex sample at a speed of between approximately 1 drop per second. In several embodiments, the volume of each drop of sulfide solution is between approximately 25uL and lOOuL. In various embodiments, the volume of each drop of sulfide solution is between approximately 40uL and 75uL, for instance approximately 50uL, 60uL, or 70uL. In various embodiments, time interval between individual drops of sulfide solution added to the latex sample is controlled, for example uniform. The sulfide solution can be added to the latex sample at room temperature and pressure.

In some embodiments of the present disclosure, the precipitated interfering metal ions are removed or separated from the latex sample. In many embodiments, the sulfide ions, which act as capture ions, bind to the interfering metal ions to form sulfide ion-interfering metal ion complexes. Such sulfide ion-interfering metal ion complexes can be of a high binding affinity and therefore be substantially unreactive. In addition, in various embodiments, the sulfide ion-interfering metal ion complexes can be easily and/or conveniently removed.

The precipitation and/or removal of interfering metal ions from the latex sample facilitate or enable quantification of magnesium ions in the latex sample with a higher accuracy. In some embodiments of the present disclosure, ammonium oxalate is added to the latex sample in a fourth process portion 140. The addition of ammonium oxalate to the latex sample facilitates or effectuates a specific precipitation of calcium ions that are present in the latex sample. The addition of ammonium oxalate to the latex sample is optional.

In several embodiments, ammonium oxalate is added to the latex sample in a controlled manner or precise manner, for instance, a controlled multi-step or incremental manner. For example, ammonium oxalate can be added to the latex sample in a similar, or substantially similar, manner as compared to the addition of sulfide ions in the second process portion 120.

The precipitation of calcium ions in the latex sample can facilitate or enable a quantification of magnesium ions in the latex sample with a higher accuracy. A fifth process portion 150 involves the performance of a complexometric titration process or technique to thereby facilitate or effectuate a quantification of magnesium ions in the latex sample.

In many embodiments, EDTA is used as a titrant in the complexometric titration process. In numerous embodiments, Erichrome black T is used as an indicator in the complexometric titration process. Other indictors, such as Erio-T indicator and Cal-red indicator can also be used in the complexometric titration process.

Generally, a change (e.g., color change) demonstrated or displayed with the aid of the indicator signals, or provides, an end point of the titration process. The quantity, more specifically volume, of EDTA consumed or required to produce the change (e.g., color change) can correlate to a quantity of magnesium ions that is present in the latex sample.

Complexometric Titration Process

The complexometric titration process or technique typically involves a use of EDTA as a means for volumetric analysis. More specifically, the complexometric titration process is used for quantifying an ion (e.g., magnesium ion) found in a test mixture or sample (e.g., latex sample).

EDTA is added into the test sample or mixture (e.g., latex sample), which includes an indicator (e.g., Erichrome black T). The indictor allows a color change to signal an end point to a reaction between EDTA and the ion (e.g., magnesium ion). An EDTA molecule has four acidic protons, and hence the formation of EDTA-metal ion complex is dependent upon pH value.

Accordingly, in many embodiments of the present disclosure, the complexometric titration process using EDTA to quantify magnesium ions present in a mixture or sample (e.g., latex sample) is performed at a pH value of approximately 10.0 or higher. In some embodiments, the pH value during the complexometric titration process with EDTA as a titrant is approximately 10.3.

In numerous embodiments, the quantity or volume of EDTA required or consumed upon reaching an end point of the titration is used to determine, correlate to, calculate, or obtain a magnesium quantity, amount, or concentration in the latex sample. More specifically, in most embodiments, a value of the volume of EDTA consumed, and hence a concentration of EDTA used, in the titration process correlates to the quantity (e.g., concentration) of magnesium ions present in the latex solution.

A sixth process portion 160 involves addition of a powder including carbonate ions, compounds, or components to the latex sample. In numerous embodiments, the powder is added immediately, or substantially quickly, after the titration process (i.e., after the end point of the titration process is reached). In particular embodiments, the powder is added not more than 5 minutes, and preferably less than 3 minutes, after the end point of the titration process is reached. The latex sample with the added powder can be shaken and left at room temperature for at least one minute. In many embodiments, the powder includes at least one of sodium carbonate and calcium carbonate. In several embodiments, an excess of carbonate ions, compounds, or components as required to react with any sulfide ions that may still be present in the latex sample is added to the latex sample. For example, in various embodiments, at least approximately 0.0005 grams of the powder is added to the latex sample.

In many embodiments, the carbonate ions, compounds, or components provided by the powder react with sulfide ions to prevent formation of sulfide gases (e.g., hydrogen sulfide gas). Accordingly, in many embodiments, the reaction between carbonate ions and sulfide ions prevents generation of a smell or odor that is associated with production of sulfide gases (e.g., hydrogen sulfide gas).

In order that the embodiments of the present disclosure may be more clearly understood as to matters of principle as well as to methods of quantifying magnesium ions present in a mixture, solution, or sample (e.g., latex sample), several non-limiting examples are provided below. In the examples described below, a reference made to particular processes, process portions or steps, compositions, apparatuses, devices, and/or components thereof, can be understood to include variants, and/or alternatives, to that which is described above within the scope of the present disclosure.

EXAMPLE ONE Method for Preparing a Field Latex Sample

A method or process for preparing a field latex sample according to an embodiment of the present disclosure is described in example one. The method involves adding a selected volume of deionised water to a selected quantity (e.g., weight or volume) of a latex mixture to dilute the latex mixture. More specifically, approximately 99.0mL of deionised water is added per 1.00 gram of the latex mixture to produce a diluted latex mixture.

The method also includes adding an alkaline solution, mixture, or composition that includes borax and sodium hydroxide into the dilute latex mixture. The alkaline solution is added in a controlled manner to adjust the pH value of the diluted latex mixture to at least approximately 10.0. The field latex sample formed can be maintained or kept at room temperature and pressure.

While the method of example one uses an alkaline solution including borax and sodium hydroxide, other types of alkaline solutions, mixtures, or compositions of different constitutions (e.g., an alkaline solution including potassium hydroxide) can be added to the diluted latex mixture for adjusting the pH value of the latex mixture.

EXAMPLE TWO

Method for Preparing a Concentrated Latex Sample

A method or process for preparing a concentrated latex sample according to an embodiment of the present disclosure is described in example two.

The method includes diluting a selected quantity (e.g., weight or volume) of field latex with a selected volume of deionised water. More specifically, the method includes adding approximately lO.OmLof deionised water to approximately 10.0 gram of field latex.

The method also includes subsequently adding or introducing a selected volume of approximately 25% concentrated acetic acid into the diluted field latex. The addition of the 25% concentrated acetic acid is added into the diluted field latex in a controlled, more specifically drop-wise, manner. In the method of example two, approximately 5.0mL of 25% concentrated acetic acid is added in a drop-wise manner. The addition of the concentrated acetic acid can help to coagulate latex particles such that an end point of a subsequent complexometric titration process can be observed more easily and/or more accurately. Generally, the addition of acetic acid helps to separate rubber particle(s) that may be present in the diluted latex mixture.

The method for preparing the concentrated latex sample of example two further includes neutralizing the latex mixture with added acetic acid using a volume of sodium hydroxide (NaOH). More specifically, approximately 0.5 molar of NaOH is added to neutralize lO.OmL of the latex mixture.

The preparation of the concentrated latex sample further involves adding a volume of an alkaline solution, mixture, or composition that includes Borax and NaOH to the neutralized latex mixture to adjust the pH value of said neutralized latex mixture to at least approximately 10.0.

EXAMPLE THREE

A Method For Selectively Precipitating Interfering Metal Ions Using Sulfide Ions

A method or process for selectively precipitating interfering metal ions, more specifically at least one of zinc, copper, iron, manganese, and other transition metal ions, is described in example three.

As mentioned above, the selective precipitation of an ion (i.e., an interfering metal ion) involves adding capture ions with a higher binding affinity for that interfering metal ion. Binding of an interfering metal ion to a capture ion results in formation of an interfering ion- capture ion complex. Generally, the interfering ion-capture ion complex possesses a low solubility constant and therefore can be selectively precipitated and removed from the latex sample.

In the method of example three, ammonium sulfide solution is used for facilitating the selective precipitation of interfering metal ions. The ammonium sulfide solution includes, or provides, sulfide ions. More specifically, the concentration of sulfide ions of, or provided by, the ammonium sulfide solution is approximately 2.4mM per 10 grams of latex sample.

Approximately 4.0mL of ammonium sulfide solution having a sulfide ion concentration of approximately 0.6M is added to a latex sample that includes approximately 10.0 grams of latex. The ammonium sulfide solution is added to the latex sample in a controlled, more specifically a drop-wise manner. The drop-wise addition of ammonium sulfide solution facilitates enhanced (e.g., increased) contact and/or interaction between the sulfide ions and the interfering metal ions to thereby increase at least one of rate and extent of reaction between the sulfide ions and the interfering metal ions. The latex sample with added ammonium sulfide solution can be agitated, for instance using a magnetic stirrer, to facilitate enhanced contact and/or interaction between the sulfide ions and the interfering metal ions. Alternatively, the latex sample with added ammonium sulfide solution can be manually shaken.

Subsequently, the latex sample with the ammonium sulfide solution added thereto is left alone at room temperature for at least approximately 5 minutes. The sulfide ions provided by the ammonium sulfide solution react with the interfering metal ions (i.e., metal ions present in the latex sample that are not magnesium ions) to form an interfering metal-sulfide ion complex, which can be removed or which is no longer capable of reacting with EDTA in a subsequent titration (e.g., complexometric titration) process.

EXAMPLE FOUR

Effectiveness of Cyanide Ions and Sulfide Ions in Precipitating Magnesium and Zinc Ions

Experiments were conducted to measure the effectiveness of cyanide ions and sulfide ions in respectively masking and precipitating zinc ions (which is an example of an interfering metal ion in latex samples). In addition, experiments were conducted to measure the effectiveness of cyanide ions and sulfide ions in respectively masking and precipitating zinc ions.

Experimental Procedures

In the experiments of example four, two standard solutions (of approximately lOmL each) that include magnesium ions (hereinafter referred to as magnesium samples (1) and (2)) and two standard solutions (of approximately lOmL each) that include zinc ions (hereinafter referred to as zinc samples (1) and (2)) are provided. Magnesium samples (1) and (2) have an identical concentration of magnesium ions, more specifically approximately 8.3 μηιοΐε of magnesium ions. Zinc samples (1) and (2) have an identical concentration of zinc ions, more specifically approximately 3.1 μιηοΐε of zinc ions.

To magnesium sample (1), a volume (i.e., approximately 4.0mL) of potassium cyanide (providing cyanide ions) was added. To magnesium sample (2), a volume (i.e., approximately 4.0mL) of ammonium sulfide (providing sulfide ions) was added.

To zinc sample (1), a volume (i.e., approximately 4.0mL) of potassium cyanide (providing cyanide ions) was added. To zinc sample (2), a volume (i.e., approximately 4.0mL) of ammonium sulfide (providing sulfide ions) was added.

The concentration of cyanide ions provided to each of magnesium sample (1) and zinc sample (1) was similar, more specifically approximately 2.4mM. In addition, the concentration of cyanide ions provided to each of magnesium sample (2) and zinc sample (2) was similar, more specifically approximately 2.4mM.

Each of potassium cyanide and ammonium sulfide was added to the samples in a controlled or precise manner. More specifically, each volume of potassium cyanide and ammonium sulfide was added to the samples in a drop-wise manner. After addition of potassium cyanide and ammonium sulfide to the samples, the resultant mixtures were left at room temperature for 5 minutes.

Each resultant mixture was subsequently titrated with approximately 0.005 mol/dm ³ of EDTA as titrant, using approximately 0.1 gram of Erichrome black T as an indicator. A change in the color from wine-red to clear blue displayed by Erichrome black T indicates an end point of the titration process. A volume of EDTA that was consumed by the titration process with each resultant mixture (hence each sample) was recorded. The volume of EDTA consumed with each resultant mixture (hence each sample) was used for calculating the quantity (e.g., μηιοΐε) of EDTA that reacted, or was consumed, by the magnesium or zinc ions in the mixture. The quantity (e.g., μιηοΐε) of EDTA is then used for determining the amount (e.g., concentration) of magnesium or zinc ions present each sample.

Results and Discussion

As illustrated in Figure 2, the amount of EDTA consumed during titration process using magnesium sample (1) and zinc sample (1), to which cyanide ions were added, were 10.0 μηιοΐε and 2.83 μηιοΐε, respectively. This indicates that cyanide ions preferentially, or are more capable of masking zinc ions over magnesium ions. In addition, results indicate that cyanide ions are not able to completely, or essentially completely, mask zinc ions.

Figure 2 also shows that the amount of EDTA consumed during titration process using magnesium sample (2) and zinc sample (2), to which sulfide ions were added, were 9.5 μηιοΐε and 0 μιηοΐε, respectively. This result indicates that sulfide ions also preferentially precipitate zinc ions over magnesium ions.

In addition, the results indicate that sulfide ions can completely, or essentially completely, bind to, or precipitate, zinc ions, thereby eliminating the availability of zinc ions for subsequent reaction with EDTA (as shown by the 0 μπιοΐε of EDTA consumed with titration using zinc sample (2)). The results showing that sulfide ions can completely, or essentially completely, bind to, or precipitate, zinc ions is significant and unexpected and/or surprisingly good.

On the contrary, when cyanide ions were used, zinc ions were still present, and available, for reaction with EDTA. While cyanide ions were able to selectively precipitate zinc ions, cyanide ions were not capable of completely, or close to completely, precipitating zinc ions.

Results obtained with the experiments of example four are surprisingly better then expected. The experiments of example four show that sulfide ions, for instance provided by ammonium sulfide, are significantly and/or unexpectedly more capable of precipitating zinc ions as compared to cyanide ions.

Furthermore, it is believed that sulfide ions can also facilitate an enhanced precipitation of certain other ions (e.g., transition metal ions such as copper and manganese) as compared to cyanide ions. Results obtained with the experiments of example four are believed to be replicable, or similar, with other transition metal ions such as copper and manganese. EXAMPLE FIVE

Relative Effectiveness of Sulfide Ions and Cyanide Ions for Selective Precipitation of Zinc ions in a Latex Sample

Experiments were conducted to evaluate the relative effectiveness of sulfide ions and cyanide ions in masking or removing zinc ions (which are representative interfering metal ions or transition metal ions) present in a latex sample.

As described above, magnesium ions in a mixture or sample (e.g., latex sample) can be quantified using a titration process with EDTA as a titrant. However, EDTA can also react with other metal ions (which are known as interfering metal ions) besides magnesium ions, for instance zinc ions. The reaction between EDTA and interfering metal ions such as zinc ions gives rise to a positive error in the titration process (i.e., a higher quantity of EDTA consumed during the titration process) with the sample. Accordingly, for increased accuracy in quantifying magnesium ions, the interfering metal ions should first be precipitated and/or removed. In example five, experiments were performed to compare the relative capability of cyanide ions versus sulfide ions to precipitate zinc ions present in a latex sample through a comparison of determined magnesium ion concentration in the latex sample.

Experimental Procedures

Three groups or batches of latex samples, more specifically concentrated latex samples, were prepared.

Batch 1 (Control):

Approximately 10.0 mL of diluted latex mixture or sample (i.e., latex sample diluted in distilled water for field latex and 25% acetic acid for concentrated latex), and an alkaline solution (e.g., a solution including borax and NaOH) to adjust the pH value of the latex sample to approximately 10.0. No zinc ions were added to the latex samples of Batch 1, which functions as a control group in the experiments of example five. Batch 2 (Including Cyanide Ions to Mask Zinc Ions):

Approximately 10.0 mL of diluted latex mixture or sample (i.e., latex sample diluted in distilled water for field latex and 25% acetic acid for concentrated latex), and a buffer including NHs/NI^Cl (i.e., a NH ₃ / H C1 buffer).

The NH3/NH4CI buffer is prepared by weighing 67.5 gram of ammonium chloride (NH ₄ CI) and dissolving in 250cm of water, then mix with a volume of 570cm of 25% ammonia solution (NH3). Dilute the whole solution to obtain a total solution of 1 litre. The pH of the latex samples of batch 2 is approximately 10.5.

A known concentration of Zinc ions was added to the latex sample. Approximately 4.0mL of potassium cyanide solution with approximately 0.6M of cyanide ions was added to the latex samples of batch 2.

Batch 3 (Including Sulfide Ions to Precipitate Zinc Ions): Approximately lO.OmL of diluted latex mixture or sample (i.e., latex sample diluted in distilled water for field latex and 25% acetic acid for concentrated latex), and an alkaline solution (e.g., a solution including borax and NaOH) to adjust the pH value of the latex sample to approximately 10.0.

A known concentration of Zinc ions was added to the latex sample. Approximately 4.0mL of ammonium sulfide solution with approximately 0.6M of sulfide ions was added to the latex samples of batch 2.

Each latex sample from each of batches 1 to 3 was left at room temperature for approximately 5 minutes. The resultant latex samples were subsequently titrated with EDTA of a concentration of approximately 0.005 mol/dm ³ using approximately 0.0003 gram of Erichrome black T as an indicator in a complexometric titration process. A change in the color from wine-red to clear blue displayed by Erichrome black T indicated an end point of the titration process. The volume of EDTA consumed by the titration process for each latex sample of each of batches 1 , 2, and 3 was recorded. The volume of EDTA is used to reflect or determine the magnesium concentration presenting in latex samples.

Results and Discussion As shown in Figure 3, latex samples in batch 1 (control), which did not include zinc ions, had an average magnesium ion concentration of 18.5ppm. Accordingly, the baseline or actual magnesium ion concentration can be taken to be 18.5ppm for the latex samples of each of batches 1, 2, and 3. Therefore, the concentrations of magnesium ions determined for latex samples of batches 2 and 3 can be compared to the baseline magnesium concentration (i.e., 18.5ppm) to thereby evaluate the relative effectiveness of cyanide ions and sulfide ions in masking zinc ions.

Figure 3 shows that latex samples in batch 2, which included zinc ions, had an average magnesium ion concentration of 22.2ppm. This increase in the determined magnesium ion concentration can be attributed to the addition of zinc ions. This is to say the fraction of zinc ions that were not masked or removed from the latex samples of batch 2 caused an increase in determined magnesium ion concentration from 18.5ppm to 22.2ppm (or an equivalent to a 20% inaccuracy in the determination of magnesium ion concentration). Results indicated that cyanide ions were not capable of completely, essentially completely, or significantly masking or removing zinc ions (or interfering metal ions) in latex sample. Figure 3 also showed that the latex samples of batch 3 had an average magnesium ion concentration of 18.5ppm, which is equivalent to the determined average magnesium ion concentration batch 1 (i.e., the control batch). Results indicated that sulfide ions that were introduced or added to the latex samples of batch 3 were capable of completely or significantly precipitating zinc ions (or interfering metal ions) present in the latex samples. The results of the experiments of example five indicated that sulfide ions are significantly more capable of precipitating zinc ions as compared to cyanide ions. Results suggest that sulfide ions are capable of completely precipitating zinc ions in latex samples, thereby eliminating positive errors in determined magnesium ion concentration due to the presence of zinc ions in the latex samples. Accordingly, results indicate that the use of sulfide ions can significantly improve the accuracy of quantification of magnesium ions present in latex samples.

Furthermore, it is believed that sulfide ions can also facilitate an enhanced, or even complete, precipitation of certain other ions (e.g., transition metal ions such as copper and manganese) in latex samples as compared to cyanide ions. Results obtained with the experiments of example five in association with zinc ions are believed to be replicable, or similar, with other transition metal ions such as copper and manganese.

EXAMPLE SIX Methods or Techniques of Introducing Sulfide Ions to Latex Samples

Experiments were conducted to evaluate the effectiveness of two different methods or techniques of introducing sulfide ions to latex samples in precipitating interfering metal ions, for instance zinc ions. More specifically, experiments were conducted to compare the effectiveness of introducing sulfide ions in a single addition versus the effectiveness of introducing sulfide ions in a controlled manner for precipitating interfering metal ions.

Experimental Procedures

Two field latex samples (i.e., latex sample (1) and latex sample (2)) of equal volumes were prepared, for instance according to example one, and provided.

To latex sample (1):

Approximately 4.0mL of ammonium sulfide with a sulfide concentration of approximately 0.6M was added to latex sample (1) in a controlled manner. More specifically, the approximately 4.0ml of ammonium sulfide with a sulfide concentration of approximately 0.6M was added to latex sample (1) in a drop-wise manner, the time intervals at which the drops of ammonium sulfide were added being at least substantially uniform. In addition, volume corresponding to each drop of ammonium sulfide is also substantially uniform. To latex sample (2):

Approximately 4.0mL of ammonium sulfide with a sulfide concentration of approximately 0.6M was added to latex sample (2). More specifically, approximately 4.0mL of ammomum sulfide with a sulfide concentration of approximately 0.6M was added to latex sample (2) all at once from a dispenser in an uncontrolled, or substantially uncontrolled, manner.

After the ammonium sulfide was added to each latex sample, the latex samples were left at room temperature for approximately 5 minutes. Subsequently, the latex samples were titrated with EDTA of a concentration of approximately 0.005mol/cm ³ using approximately 0.0003 gram of Erichrome black T as an indicator in the titration process. The volume, or quantity, of EDTA consumed by the titration process was recorded. The quantity of EDTA consumed by the titration process was used to determine or calculate the concentration of magnesium ions present in the latex samples.

Result and Discussions

As shown in Figure 4, when ammonium sulfide was introduced into latex sample (1) in a controlled, more specifically drop-wise, manner, the concentration of magnesium ions in the latex sample (1) was determined to be approximately 225ppm. However, when ammonium sulfide was introduced into latex sample (2) in an uncontrolled, single addition, manner (e.g. by instantaneously pumping the 4.0mL of ammonium sulfide from a dispenser), the concentration of magnesium ions in the latex sample (2) was determined to be approximately 370ppm.

A difference in determined magnesium ion concentration of approximately 145ppm is shown or observed between the two different methods or techniques of introducing ammonium sulfide into the latex samples. In other words, an approximately 64% decrease in determined magnesium ion concentration is seen when the ammonium sulfide solution is added in a controlled, drop-wise, manner.

The higher determined magnesium ion concentration associated with the uncontrolled, single-addition, manner of ammonium sulfide introduction into latex samples can cause, or contribute to, an incomplete precipitation of interfering metal ions. Results suggest that the addition of ammonium sulfide (i.e., sulfide ions) in a controlled, or drop-wise, manner facilitates or enables an increased effectiveness in the precipitation of interfering metal ions. The enhanced precipitation of interfering metal ions, and hence a lower measurement for the concentration of magnesium ions, in a latex sample when ammonium sulfide (i.e., sulfide ions) is added in a controlled, or drop-wise manner increases accuracy of quantifying magnesium ions in latex samples (e.g., reduces the occurrence, or magnitude, of positive errors).

EXAMPLE SEVEN Relative Effectiveness of Cyanide Ions and Oxalate Ions in Masking or Precipitating Calcium Ions

Experiments were conducted to measure the effectiveness of cyanide ions and oxalate ions in masking or precipitating calcium ions. Calcium ions can be considered as interfering metal ions when quantifying magnesium ions in a latex sample using a complexometnc titration technique. Accordingly, in some embodiment of the present disclosure, oxalate ions are added to the latex sample for masking or precipitating calcium ions.

Experimental Procedures

In the experiments of example seven, two samples (hereinafter referred to as samples (1) and (2)) including magnesium ions and calcium ions were provided. Each of samples (1) and (2) has an identical magnesium and calcium concentration. More specifically lmL of a standard magnesium solution of a magnesium concentration of approximately lOOppm and a standard calcium solution of a calcium concentration of approximately lOOppm were combined to obtain each of samples (1) and (2).

To sample (1), approximately 4.0mL of potassium cyanide with a cyanide ion concentration of 4% w/v was added. To sample (2), approximately 6.0mL of ammonium oxalate [i.e., (NH ₄ ) ₂ C ₂ 0 ₄ ] with an oxalate ion concentration of approximately 6% w/v was added.

Each of potassium cyanide and ammonium oxalate was added to the samples (1) and (2) respectively in a controlled or precise manner. More specifically, each of potassium cyanide and ammonium oxalate was added to the samples (1) and (2) in a drop- wise manner.

Each resultant mixture was subsequently titrated with approximately 0.005mol/dm of EDTA as titrant, using approximately 0.1 gram of Erichrome black T as an indicator. A change in the color from wine-red to clear blue displayed by Erichrome black T indicates an end point of the titration process. A volume of EDTA that was consumed by the titration process with each of samples (1) and (2) was recorded.

The volume of EDTA consumed by the titration process with each of samples (1) and (2) was used for determining the amount (e.g., concentration) of magnesium ions present in each sample. Results and Discussion

Results as shown in figure 5 show that sample (1), in which calcium ions were masked using cyanide ions, had an average magnesium ion concentration of approximately 192ppm. In addition, results suggest that sample (2), in which calcium ions were masked or precipitated using oxalate ions, had an average magnesium ion concentration of approximately 103ppm. Because a standard magnesium solution of a known magnesium ion concentration of lOOppm was used, the accuracy of the determined concentrations of magnesium ions for each of samples (1) and (2) can be determined.

As shown in Figure 5, the determined magnesium ion concentration of approximately 192ppm for sample (1) represents an approximately 92% increase relative to the known magnesium ion concentration of lOOppm. This increase in the determined magnesium ion concentration as compared to the actual magnesium ion concentration (i.e. the increase from lOOppm to 192ppm) can be attributed to the presence of calcium ions that were not completely masked, precipitate, or removed from sample (1), and which subsequently reacted with EDTA during the titration process. Results indicate that cyanide ions are not effective in masking, precipitating, or removing calcium ions.

On the other hand, as shown in Figure 5, the determined magnesium ion concentration of approximately 103ppm in sample (2) only represents an approximately 3% increase relative to the known or actual magnesium ion concentration of lOOppm. The average determined magnesium ion concentration in sample (2), in which oxalate ions were added, is almost equivalent to the actual magnesium ion concentration. Results indicated that oxalate ions were capable of completely, or substantially, masking, precipitating, or removing calcium ions present in the latex sample. Therefore, the experiment of example seven show that oxalate ions, for instance oxalate ions as provided by ammonium oxalate, are significantly more capable of masking, precipitating, or removing calcium ions as compared to cyanide ions. Accordingly, the results of example seven suggests that oxalate ions can be used for selectively removing calcium ions in latex samples to thereby facilitate or effectuate enhanced accuracy in quantifying magnesium ions present in said latex samples.

Embodiments of the present disclosure relate to methods, processes, techniques, and/or compositions for facilitating or effectuating quantification of magnesium ions in a solution, mixture, or sample (e.g., latex sample). More specifically, sulfide ions are used to selectively precipitate interfering metal ions before a quantification of magnesium ions in the latex sample occurs. The sulfide ions are added to the latex sample in a controlled manner, more specifically in a drop-wise manner. Time intervals between drops can be uniform.

In many embodiments, an alkaline solution or buffer solution is added to the latex sample prior to the selective precipitation of interfering metal ions using sulfide ions. In several embodiments, the alkaline solution or buffer solution includes sodium hydroxide and borax. In various embodiments, the alkaline solution facilitates or enhances precipitation of the interfering metal ions using sulfide ions.

In many embodiments, the selective precipitation of interfering metal ions in the latex sample facilitates or effectuates an enhanced accuracy in quantifying magnesium ion concentration. In several embodiments, the use of sulfide ions to selectively precipitate interfering metal ions is convenient and safe. The use of sulfide ions rather than cyanide ions in manner described herein avoids toxicity issues associated with cyanide, while providing substantially more accurate results than cyanide-based techniques for quantifying magnesium concentration in latex samples.

Aspects of particular embodiments of the present disclosure address at least one aspect, problem, limitation, and/or disadvantage associated with existing methods, processes, and/or compositions for quantifying magnesium ions in a solution, mixture, or sample. While features, aspects, and/or advantages associated with certain embodiments have been described in the disclosure, other embodiments may also exhibit such features, aspects, and/or advantages, and not all embodiments need necessarily exhibit such features, aspects, and/or advantages to fall within the scope of the disclosure. It will be appreciated by a person of ordinary skill in the art that several of the above-disclosed methods, processes, compositions, or alternatives thereof, may be desirably combined into other methods, processes, and/or compositions. In addition, various modifications, alterations, and/or improvements may be made to various embodiments that are disclosed by a person of ordinary skill in the art within the scope and spirit of the present disclosure.