| Summary: | Chlorpropham, also known as isopropyl-N-(3-chlorophenyl) carbamate or CIPC is a sprout suppressant and plant growth regulator of the chemical class derived from carbamic acid (NH2COOH). The substance was first developed as a pre-emergence herbicide, and it was quickly identified as a useful potato sprout suppressant for long-term tuber storage (Marth & Schultz 1952). Today CIPC is the major sprout inhibitor used in the potato industry (UK Potato Council 2013c). As a consequence there is environmental concern about CIPC reaching the aquatic environment from potato washing plants. An RP-HPLC method for the analysis of CIPC and IPC in methanol solvent with an automatic integration method was developed and validated. The correlation coefficients for CIPC and IPC regression lines at all calibration levels (0.001–100 mg/L) were (R2>0.999) while IPC exhibited a slightly less linear calibration curve (R2>0.98) at the lowest concentration range of (0.001–0.1 mg/L). An acceptable precision of 10% based on 10 injections was obtained at the limit of quantification of 0.001 mg/L for both analytes. The 3CA was excluded at this stage as it overlapped with an extra peak which required extensive investigations. The identification led to the conclusion that the artefact peak was a methanol-oxygen peak and elimination of the methanol-oxygen peak was not possible. The evaluation of five different columns and conditions in separating the methanol-oxygen peak from 3CA in a mixture containing 3CA, IPC and CIPC was studied. For the four peaks, the best separation at low eluant concentration was obtained at 55% methanol, but the run time was considerable. In contrast, the best separation at high eluant concentration was obtained at 75% methanol; however, the methanol-oxygen peak was still incompletely separated from the IPC peak due to the high size of the methanol-oxygen peak. Further investigations were conducted to reduce the size of the methanol-oxygen peak by changing the mobile phase pH which had no effect. Changing detection wavelength from 210 – 260 nm reduced the peak size, but considerable loss in sensitivity was observed. Five different instruments were tried and at the end the Thermo HPLC system was chosen because it provided a smaller methanol-oxygen peak along with temperature control to enhance the methanol-oxygen and 3CA peak separation at 60% methanol eluant, but the run time was still very long. Therefore, to enable a compromise between baseline peak resolutions as well as high-throughput separations; two separate methods for 3CA and CIPC, including IPC were developed and validated. The precision for both analytes at two levels of 0.01 and 1.0 mg/L based on 10 injections was ≤ 1%, the calibration curves at all levels were (R2>0.999) and the limit of quantification was 0.001 mg/L. Preparation of CIPC, IPC and 3CA standards in water from stock solutions in methanol and directly by dissolution in water was investigated. The peak areas were not affected even at 0% methanol concentration and the peak shapes were sharper than that in methanol without affecting the peak area. This validated the use of water as sample solvent to carry out the analysis by HPLC. To successfully prepare CIPC, IPC and 3CA in 100% water, it was necessary to develop methods for preparation and handling aqueous solution of CIPC, IPC and 3CA. The solubility of CIPC and IPC were studied. Both CIPC and IPC have low solubility in water while 3CA has higher solubility and dissolved quite rapidly. The solubility time curve for CIPC showed a gradual concentration increase from initial time until day 3 stirring but after that the solubility was consistent and values of 106, 89 and 61 mg/L CIPC were obtained at 25°C, 22°C and 4°C respectively. IPC exhibited similar solubility behaviour and the corresponding values were found to be 222, 200 and 140 mg/L at same temperatures respectively.The solubility results agreed with the literature values. Stock solutions and standards in aqueous solution were found to be stable on storage at 4°C (refrigerator) and ~20°C (lab temperature) for up to 90 days.For this work it was necessary to investigate possible CIPC, IPC and 3CA adsorption from aqueous solutions by glassware and filters. All plastic glassware were avoided as they have measurable adsorption (20-40%) for the analytes, except high clarity polypropylene. In contrast, glass materials particularly borosilicate and soda glass provided nearly zero adsorption for all three analytes. Although it was possible to identify suitable glassware that did not adsorb CIPC, IPC and 3CA it was necessary to discard the first 25 mL of filtrate to overcome adsorption onto filters (Cellulose, Glass microfiber, PTFE and Nylon). The Glass microfiber, type GF/B filter, has a pore size of 1.0 µm and is often used as a prefilter. However, the 25 mL discarding from filtrate was suitable only for filtering sample larger than 25 mL. For small scale filtration, a much smaller 0.2 µm PTFE filter in a 17 mm chemically resistant polypropylene housing disk attached to 3 mL BD syringe was used and only 1.5 mL of the sample was required to saturate the filter. A liquid-liquid extraction method with vortex mixer (LLE-Vortex) was successfully developed and validated for the extraction of CIPC and 3CA from dilute soil–water suspensions (0.001 g/mL) with a high recovery 98%–100% and RSD% less than 1.34%. In addition, the method was reliable for extraction from high soil suspensions formed with 0.02 g/mL of soil and for 0.1 g/mL of soils with low adsorption capacity. The average precision of extracting CIPC at 0.02 g/mL and 0.1 g/mL soil content was 1.6% and 3.2% while more precise extraction observed for 3CA of about 0.91% and 1.86%, respectively. However, the extraction method did not work for soil suspension with the highest organic matter content and concentration equal or more than 0.1 g/mL. Investigations were carried out to examine the adsorption- desorption behaviour of CIPC and 3CA from aqueous solutions onto different clay and sandy air dried soils. The suitable contact time of two days using 1 g material size was determined. At all temperatures, CIPC and 3CA were strongly adsorbed in clay soils while only slightly adsorbed in sandy soils. A paired t-test was used to compare between the adsorption at 5°C and 30°C for CIPC and 3CA and concluded that there was a statistically significant difference between the two temperatures for both analytes (p-value < 0.05). The effect of pH was also studied and it was found that the soil pH had a negligible impact on the adsorption of CIPC, while for 3CA the adsorption at low and high pH was significant (p-value <0.05). The data was fitted to a Langmuir isotherm (R2=0.91-0.98) and adsorption maxima calculated. The maximum adsorption capacities for CIPC in Downholland 1A, Downholland 2A, Midelney 2A, Midelney 1A, Midelney 1B, Dreghorn 1A, Dreghorn 1B, Quivox A and Quivox B were 1583, 668, 714, 927, 215, 325, 243, 355 and 194 µg/g respectively and for 3CA were 1024, 1104, 550, 651, 292, 278, 317, 239 and 162 µg/g respectively. The main determining factor was soil organic matter. Desorption for CIPC and 3CA from soils increased with reducing both carbon and LOI percentage. In addition, investigations were extended to study the adsorption of CIPC and 3CA in oven dried plant waste materials. The data was also fitted to a Langmuir isotherm (R2=0.96-1.00) and adsorption maxima calculated. The maximum adsorption capacities for CIPC in mixed bark, B&Q garden peat, Miracle-Gro compost, Pine needles, Scots pine bark and Birch bark were 3090, 2968, 2973, 3636, 3004 and 2581 µg/g respectively and for 3CA were 2914, 2724, 2953, 2787, 2358 and 2568 µg/g respectively. The removal of chlorpropham from two river water types was studied in laboratory incubation experiments at two temperatures and different treatments of carbon, nitrogen, phosphorus, Fulvic acid and soil extracts.
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