Environmental Laboratory Table 1. Summary of iopromide concentration determined in all samples measured
15
locations near water treatment plants. The water samples were
filtered through 0.7 µm filters and then extracted using an automated solid-phase extraction (SPE) system. 200 mg hydrophilic- lipophilic balance (HLB) cartridges were first preconditioned with 5 mL of methyl tertiary butyl ether (MTBE), followed by 5 mL of methanol and 5 mL of HPLC grade water. 1 L of each sample was then loaded onto a cartridge at a fl ow rate of 15 mL/ min, after which the cartridges were rinsed with HPLC grade water followed by drying with nitrogen gas for 30 minutes. Adsorbed analytes were then eluted into 15 mL graduated conical tubes with 5 mL of methanol followed by 5 mL of 10/90 (v/v) methanol/MTBE solution. The eluent was then
evaporated to a total volume less than 100 µL under flowing nitrogen followed by reconstitution to 1.0 mL total volume using methanol. 50
µL of this extract was then diluted with 950 µL of HPLC grade water to give the final extract used for IC-ICP-MS analysis.
These diluted extracts were injected into an Agilent 1260 HPLC coupled to an Agilent 7700x ICP-MS, with an injection volume of 500
µL. The chromatographic separation was performed using a Dionex AG16 4 x 50 mm guard column followed by a Dionex AS16 4 x 250 mm analytical column. A gradient elution from 2–90 mM sodium hydroxide (NaOH) was established, using a binary gradient consisting of reagent water (A) and 100 mM NaOH (B) with a constant flow rate of 1.0 mL/min. Gradient parameters were as follows: 2% B for 18.5 minutes then increased linearly for 3.5 minutes to 40% B and held for two minutes, finally stepping up to 90% B and holding for six minutes. The gradient returned to 2% B for five minutes at the end of the run, to re-equilibrate the column, giving a total run time of 35 minutes. A 25 second needle wash using 10% aqueous methanol was used following all injections of standards and samples.
The Agilent 7700x ICP-MS was operated with HMI sample introduction (0.6 L/min dilution gas, 0.5 L/min carrier gas, sample depth = 9 mm) and in helium collision mode (He flow 3.5 mL/min). Iodine (m/z 127) intensity was monitored in time-resolved analysis (TRA) mode using a 2 second integration time over a 37 minute time window. The use of HMI allows for extended analysis of high matrix samples with minimal matrix deposition in the interface cones, and the use of the He collision cell removes potential polyatomic interferences on masses 127 such as 126
XeH+ . A calibration curve for
iopromide was prepared using aqueous standards with concentrations of 0.0, 0.1, 1, 10, 100 and 1000 ppb of intact compound (Figure 3).
Results and discussion
Using the method described, we have been able to detect iopromide in all non-zero standards used in our study. The chromatogram obtained for the 0.1 ppb injection is clearly distinguishable from the blank injection (Figure 2), and the calibration curve is linear over four orders of magnitude (Figure 3). This concentration range encompasses the levels at which iopromide has been observed in environmental waters including undiluted wastewater effluent.
Figure 4: Extracted ion chromatogram (m/z 127) of a representative sample indicating the presence of various iodinated compounds in water extracts
The standards and samples in this report were analysed during a 24 hour continuous sequence. The results obtained from this sequence are shown in Table 1. The other CCVs analysed at the end of this sequence all agreed with their predicted values within approximately 10%.
In addition to iopromide, several other iodine containing compounds
were detected in our chromatograms (Figure 4). These unknown species can be quantified based on their iodine content, using compound-independent calibrations (CIC), where the iodine content of an unknown compound is calibrated using the iodine response for a known compound, in this case iopromide. ICP-MS is ideally suited
Table 2: Summary of the concentrations of iodinated compounds (expressed as iodine concentration) measured in all extracts. Note that the results for all compounds in- cluding iopromide are expressed as iodine concentration, so the reported values shown for iopromide expressed as iodine are approximately half the actual iopromide concentrations shown in Table 1.
Figure 3: Calibration curve (log log) obtained for iopromide. The concentration axis is in ppb iopromide and the calibration points are at 0.0, 0.1, 1, 10, 100, and 1000 ppb of iopromide. Inset table lists calibration standard responses.
www.envirotech-online.com AET Annual Buyers’ Guide 2013
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