Determination of 8 Inorganic Anions in Environmental Samples Using a NovaChrom NovaIC A1 Column (Carbonate System)

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This study presents a method for the determination of inorganic anions in water, according to standard HJ 84-2016, using a NovaChrom NovaIC A1 (Carbonate System) column (4.0 × 250 mm). The results are provided for your reference.

Keywords: Ion chromatograph, Environment, Surface water, Inorganic anions, HJ84-2016

1.Experiment

1. Main Instruments and Reagents

Ion chromatograph: Conductivity detector, anions suppressor, AS3100 autosampler.

Analytical column: NovaIC A1, 4.0×250mm，5μm

Guard column: HS-5AG, 4×30 mm

Fluoride standard solution (1000mg/L）

Chloride standard solution (1000mg/L)

Nitrite standard solution (1000mg/L)

Bromide standard solution (1000mg/L)

Phosphate standard solution (1000mg/L)

Sulfate standard solution (1000mg/L)

Sodium sulfite standard stock solution (1000mg/L)

Accurately weigh 1.5750g of sodium sulfite and dissolve it in an appropriate amount of water. Transfer the solution completely into a 1000mL volumetric flask. Add 1mL of formaldehyde to stabilize the sulfite ions (to prevent oxidation). Dilute the solution to the mark with water and mix thoroughly. Transfer the solution to a polyethylene bottle. It can be stored for up to one month under refrigeration (below 4°C), protected from light, and in a sealed condition.

Formaldehyde solution (CH₂O), 40% assay

Sodium sulfite (Na₂SO₃), guaranteed reagent (GR)

Disposable syringe (5mL)

Aqueous microporous membrane filter (0.45μm)

1.2 Solution Preparation

1.2.1 Standard Intermediate Solution

Accurately pipette 0.5mL of fluoride standard solution, 10mL of chloride standard stock solution, 0.5mL of bromide standard stock solution, 0.5mL of nitrite standard stock solution, 5mL of nitrate standard stock solution, 2.5mL of phosphate standard stock solution, 2.5mL of sulfite standard stock solution, and 10mL of sulfate standard stock solution into a 50mL volumetric flask. Dilute to the mark with water and mix thoroughly to prepare a mixed standard intermediate solution containing 10mg/L fluoride, 200mg/L chloride, 10mg/L bromide, 10mg/L nitrite, 100mg/L nitrate, 50mg/L phosphate, 50mg/L sulfite, and 200mg/L sulfate.

1.2.2 Series of Standard Working Solutions

Accurately pipette 1.00mL, 2.00mL, 5.00mL, 10.0mL, and 20.0mL of the mixed standard intermediate solution sequentially into a series of 100mL volumetric flasks. Dilute to the mark with ultrapure water and mix thoroughly to prepare a series of five mixed standard working solutions at varying concentrations. The specific concentrations of the standard series are shown in Table 1.

Table 1 Standard Curve Concentration Gradient

1.3 Instrument Working Conditions

Table 2

1.4 Sample Pretreatment

For clean water samples free from interfering substances such as hydrophobic compounds, heavy metals, or transition metal ions, injection shall be performed using a disposable syringe equipped with an aqueous microporous membrane syringe filter. For complex water samples containing interfering substances, effective removal must be carried out with appropriate pretreatment cartridges prior to injection.

2. Result and Discussion

2.1 Standard Curve Linearity Verification

The series of standard working solutions prepared in section 1.2.2 were analyzed under the working conditions specified in section 1.3. The resulting multi-overlay chromatogram of the standard curve is shown in Fig 1, and the corresponding linear plot is presented in Fig 2, demonstrating good linearity.

Fig 1 Overlay Chromatogram of Standard Solutions

Table 3 Linearity of the 8 ions

2.2 Limit of Detection (LOD) Validation

When the injection volume is 25μL, the detection limits of this method are: fluoride ions 0.006mg/L, chloride ions 0.007mg/L, nitrite ions 0.016mg/L, bromide ions 0.016mg/L, nitrate ions 0.016mg/L, phosphate ions 0.051mg/L, sulfite ions 0.046mg/L, and sulfate ions 0.018mg/L. The test results for the samples are shown in Figure 3 and Table 4 below. The theoretical detection limits are superior to those of the standard method.

Fig 2 Chromatogram for LOD

Table 4 Data for Limit of Detection (LOD)

2.3 Sample and Spiked Sample Repeatability Test

The surface water samples spiked at low, medium, and high concentration levels and pretreated according to the procedure in section 1.4 were analyzed in seven replicate injections under the instrumental conditions specified in section 1.3. The corresponding chromatograms are shown in Figures 3, 4, and 5, respectively. The obtained RSD values for retention time ranged from 0.021% to 0.167%, and peak area ranged from 0.021% to 0.167%. The spike recovery rates for all ions fell within the range of 91.1% to 105.3%, demonstrating excellent performance.

Fig 3 Repeatability Test Chromatogram for Low-Concentration Spiked Surface Water Samples

Fig 4 Fig 3 Repeatability Test Chromatogram for Medium-Concentration Spiked Surface Water Samples

Fig 3 Repeatability Test Chromatogram for High-Concentration Spiked Surface Water Samples

3.Conclusion

This study employed the NovaChrom NovaIC A1 column (4.0 × 250 mm, 5µm; carbonate system) for the determination of inorganic anions in water following Standard HJ 84-2016. The results demonstrated excellent linearity and superior detection limits. The RSD values for the retention times of the eight inorganic anions ranged from 0.021% to 0.167%, while those for peak areas ranged from 0.111% to 0.959%. The spike recovery rates for all eight ions fell within 91.1%–105.3%. The NovaIC A1 column fully meets all requirements specified in Standard HJ 84-2016 for the analysis of inorganic anions in water.