Table of ContentsSummaryIntroductionExperimentalResultsDiscussionConclusionSummaryInorganic anions were determined and quantified in tap, stream, and groundwater samples using chromatography ionic. Chloride, bromide, nitrate and sulfate standards were prepared ranging from 10.27 to 0.10 mM, 0.43 to 0.08 mM, 0.356 to 0.008 mM and 0.8 to 0.2 mM for these respective ions . These standards and a five-ion standard containing fluoride, chloride, nitrate, phosphate, and sulfate were used to determine the ions present in the samples by comparing retention times. Linear regression techniques were used to plot relationships between concentration and conductivity, which allowed quantification of the ions present. For stream water, tap water, and groundwater samples, sulfate concentrations were 248 ± 22 μM, 796 ± 70 μM, and 720 ± 63 μM; nitrate concentrations were 10.7 ± 0.5 μM, 23.3 ± 1.2 μM, and 373 ± 19 μM; and the chloride concentrations were 727 ± 27 μM, 763 ± 29 μM, and 1820 ± 73 μM in the samples, respectively. The groundwater sample additionally contained 129 ± 16 µM bromide. All concentrations were determined within a 99.7% confidence interval. All water samples tested positive for the presence of unquantifiable traces of fluoride. The R2 values ​​of the standard curves were 0.9991 for chloride, 0.9917 for bromide, 0.9973 for nitrate, and 0.9980 for sulfate, showing a strong correlation between concentration and conductivity. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essayIntroductionMany different anions can be present in aqueous samples, in varying concentrations and oxidation states. Some of these ions play an important role as micronutrients and fertilizers, while others are toxic to human and animal life. For example, the metabolism of nitrates gives rise to nitrite intermediate 1, which then oxidizes the iron present in hemoglobin, thereby preventing the transport of oxygen in humans when it is in high enough concentration in a process called methemoglobinemia 2. However, this same ion is an important nutrient and source of nitrogen. for plants used in agriculture 3. Similarly, many other ions such as sulfate, chloride, phosphate and fluoride appear in water samples 4. Ion chromatography (Figure 1) is a useful method for the detection and quantification of anions and cations in aqueous media. 5. When measuring anions, an eluent, in this case an aqueous solution of carbonate and hydrogen carbonate, is pumped through the column and these ions interact with the positively charged quaternary ammonium groups on the beads of the packing material of the column. The sample is loaded into an injector that holds μL portions of the analyte in the sample loop, which then injects the sample into the guard column. The precolumn contains identical packing material to the separation column and is used to remove debris before it reaches the separation column. The sample then flows into the separation column, as the analyte ions pass through the column they displace the eluent ions, interacting with the positively charged functional groups, these different ions separate into different bands at the within the column due to factors such as the charge of the anion. , hydrated rays and its ability to contribute to disruptinghydrogen bonds in the surrounding water. These different factors affect how long the ion stays in the column, the retention time, allowing halides like fluoride to pass through the column much more quickly than others like sulfate. After the column, a suppressor is used to reduce the eluent background, by exchanging Na+ for H+ from the acidic regenerant across a membrane, which increases sensitivity for analyte anions. As the anions leave the column and then the suppressor they cause a change in the conductivity of the solution, this is measured by a pair of electrodes in the conductivity detector as the eluate passes through a flow cell. The change in conductivity is a linear relationship proportional to concentration (equation 1) where Λ is the molar conductance, κ is the electrolytic conductivity, and c is the concentration. The electrolytic conductivity (equation 2) is linked to the distance d between the electrodes, to the surface area A of the electrodes and to the conductance G between the electrodes. The conductivity signal is recorded by a computer and displayed as a chromatogram, displaying maximum conductivity as a function of retention time. Λ = κ/c (1) κ = d/AG (2) Figure 1. Schematic of an ion chromatograph Concentration of an ion box sample then be determined by measuring the conductivity of a set of standard solutions by ion chromatography and plotting the integral of the conductivity over the elution time of the analyte versus the sample concentration. The use of linear regression techniques then gives the relationship between the peak area in µS·min and the concentration, where dividing the measured integral area of ​​the sample by the first derivative of the determined linear relationship gives the concentration of the sample. ExperimentalA Dionex ICS – 1100 RFIC ion chromatograph with a flow rate of 1.2 ml/min was used to determine and quantify the concentration of anions present in tap water, groundwater and water samples. stream. A five-ion standard containing fluoride, chloride, phosphate, sulfate, and nitrate was used to determine the retention times of these ions with the settings used on the instrument. The retention times of the standards were compared to those of the samples to determine which ions were present. Standard curves were established for chloride, sulfate, nitrate and bromide to find the linear relationship between concentration and peak area of ​​the chromatogram. Standards ranged from 10.27 to 0.10 mM for chloride, 0.43 to 0.08 mM for bromide, 0.356 to 0.008 mM for nitrate, and 0.8 to 0.2 mM for sulfate. . All standards were diluted with ultra pure deionized water, MQ water, with a purity of 18.2 MΩ.cm at 25 °C, in 10 ml volumetric flasks. All glassware, except that used in chloride sample preparation, was acid washed with 10% hydrochloric acid and rinsed with MQ water to remove contaminants. Some water samples were diluted 1 to 10 due to high ion concentrations to avoid signal clipping, trailing or poorly formed peaks in the chromatogram. The concentration of different ions in the water samples was calculated by dividing the peak area by the slope of the standard curve for the respective ions. Results The stream water sample was determined to contain 727 ± 27 μM chloride, 10.7 ± 0.5 μM nitrate, and 248 ± 22 μM sulfate. Tap water contained 763 ± 29 µM chloride, 23.3 ± 1.2 µM nitrate, and 796 ± 70 µM sulfate. Groundwater contained 1,820 ± 73 μM chloride, 373 ± 19 μM nitrate, 720 ± 63 μM sulfate, and 129 ± 16 μMbromide. These concentrations were all determined within a 99.7% confidence interval. All water samples contained unquantifiable traces of fluoride. The standard curves (Figure 2) showed strong linearity between concentration and peak area with R2 values ​​of 0.9991 for chloride, 0.9917 for bromide, 0.9973 for nitrate and 0.9980 for sulfate. The ions present in the samples were determined by comparing the retention times to standards. From the 5-ion standard, the retention times for fluoride were 2.74 minutes, chloride 3.77 minutes, nitrate 6.16 minutes, phosphate 8.25 minutes, and sulfate 8.25 minutes. 10.01 minutes. The bromide retention time, 5.48 min, was determined by preparation of a separate standard. The retention times of the peaks in tap water were 2.72 min, 3.79 min, 6.28 min, and 10.10 min. The maximum retention times in stream water were 2.72 min, 3.81 min, 6.29 min, and 10.14 min. The maximum retention times in groundwater were 2.72 min, 3.74 min, 5.48 min, 6.21 min, and 10.09 min. These retention times matched those of the standards very well, giving a high level of confidence that the ions were correctly. The instrument's linearity limit was not determined for any of the ions; at high concentrations there was some tailing and poor resolution in the peaks for chloride. The detection limits for fluoride, chloride, nitrate, phosphate, and sulfate were 0.0065, 0.0061, 0.0115, 0.0049, and 0.0083, respectively. The limits of quantification for these same anions were 0.0218, 0.0204, 0.0384, 0.0163 and 0.0278. No amounts of phosphates were detected in any of the water samples, nor were any other peaks indicating the presence of other ions. Figure 2. Standard curves for chloride, bromide, nitrate and sulfate with linear regression formulas and R2 values. Discussion A very strong linear relationship was present between concentration and peak area, giving a high measure of confidence in the determination of anion concentrations in water samples. Stream water and tap water samples showed very similar chloride levels; however, the stream water contained approximately half the nitrate concentration and one-third the sulfate concentration of tap water. The discrepancy between tap water and stream water may be due in part to the fact that tap water sits in the pipes longer, allowing a buildup of trace ions. Another possible reason for the low concentrations of different ions in the stream water may be due to the filtration used to remove biological contamination. Some amount of anions may have been physically filtered or may be found in algae or bacteria cells collected on the filter. Groundwater had the highest levels of all ions quantified, with more than twice the chloride concentration of stream water and nearly forty times the nitrate concentration. These concentrations are expected in the groundwater sample due to leaching of minerals into the well water from which they were collected. Additionally, the level of nitrates in this sample may be due to the fertilizers used in the area where it was collected, due to the intensive farming and farming that takes place there. The presence of bromide in groundwater was unexpected and could not be determined by comparing retention times. ions in the 5-ion standard. A solution of potassium bromide was prepared and its retention time was found to be 5.48 minutes, exactly matching the unidentified peak in groundwater by chromatography..