AN96: Determination of N-Methylcarbamates by Reversed ... - Dionex

More documents

Recommendations

Info

RO OPA O N H Carbamate CHO CHO CH 3 + + H 2 O OH - 100 ° C (CH 3 ) 2 NCH 2 CH 2 SH CH 3 NH 2 pH ≥ 9 2 CH 3 NH 2 + R – OH + CO 3 - SCH 2 CH 2 N(CH 3 ) 2 N — CH 3 Fluorescent isoindole Figure 2. Postcolumn reaction chemistry of carbamate. After separation on the C18 column, carbamates are hydrolyzed by sodium hydroxide at 100° C. The resulting methylamines are then reacted with o-phthalaldehyde and N, N’-dimethyl-2-mercaptoethylamine hydrochloride (Thiofluor) to form a fluorescent isoindole compound. The details of this chemistry are shown in Figure 2. Note: The Thiofluor reagent replaces 2-mercaptoethanol, a reagent sometimes used for this application. The advantage of using Thiofluor is that it is more stable and relatively odorless. To assist in troubleshooting postcolumn chemistry issues, 1-naphthol is included in some standard carbamate mixtures, as shown in Figure 3 (peak 10). This compound is naturally fluorescent; therefore it will be the only peak present in a chromatogram when the postcolumn system is not functioning properly. Resolution and Reproducibility Figure 3 illustrates good separation of the carbamates listed in U. S. EPA Method 531.2 using the Acclaim 120 C18. Resolution for all peaks is much better than the values required in the EPA Method (≥ 1.0). Reproducibility was estimated by making 7 replicate injections of a calibration standard with concentration of 1.0 µg/L. The values of relative standard deviation (RSD) of each carbamate for retention time and for peak area are listed in Table 2. Column: Acclaim 120 C18, 4.6 mm x 150 mm Eluent: CH3CN/CH3OH/ H 2O: Gradient Temperature: 42 °C Flow Rate: 1.0 mL/min Inj. Volume: 250 µL Detection: RF-2000 Excitation: 330 nm; Emission: 465 nm 4 Determination of N-Methylcarbamates by Reversed-Phased HPLC 24084 35.4 mV 1 23 4 –14.9 5.4 7.5 10 12.5 15 17.5 20 22.5 25 27.2 Table 2: Reproducibility of retention time and peak areas for ten carbamates and two reference components Carbamates Aldicarb sulfoxide Aldicarb sulfone Oxamyl Methomyl 3-Hydroxycarbofuran Aldicarb Propoxur Carbofuran Carbaryl 1-Naphthol Methiocarb 5 6 20 20 30 30 Peaks: 1. Aldicarb sulfoxide 2 µg/L 2. Aldicarb sulfone 2 3. Oxamyl 2 4. Methomyl 2 5. 3-Hydroxy carbofuran 2 6. Aldicarb 2 7. Propoxur 2 8. Carbofuran 2 9. Carbaryl 2 10. 1-Naphthol 2 11. Methiocarb 2 12. BDMC 2 7 8 Minutes 9 10 Retention Time RSD (%) Peak Area RSD (%) 0.11 3.09 0.08 1.39 0.08 1.04 0.06 0.99 0.06 1.39 0.05 1.06 0.07 2.04 0.08 2.98 0.04 0.83 0.03 0.79 0.03 2.78 15 11 12 Figure 3. Standard mixture of 10 carbamates (2 µg/L) plus two reference compounds (peaks 10 and 12) with 250 µL injection. 0 24085
Column: Acclaim 120 C18, 4.6 mm x 150 mm Eluent: CH3CN/CH 3OH/ H 2O: Gradient Temperature: 42 °C Flow Rate: 1.0 mL/min Inj. Volume: 250 µL Detection: RF-2000 Excitation: 330 nm; Emission: 465 nm 22.3 mV Peaks: 1. Aldicarb sulfoxide 2. Aldicarb sulfone 3. Oxamyl 4. Methomyl 5. 3-Hydroxy carbofuran 6. Aldicarb 7. Propoxur 8. Carbofuran 9. Carbaryl 10. 1-Naphthol 11. Methiocarb –14.3 4 6 8 10 12 14 16 18 20 22 24 140 B 4 9 mV A 1 1.0 µg/L 0.5 µg/L 0.2 µg/L 10 µg/L 5 µg/L 2 µg/L 2 3 1 4 23 5 6 5 6 9 10 –51 3.3 6 8 10 12 14 16 18 20 22 24 Minutes 24086 Figure 4. An overlay of chromatograpms of carbamates with concentrations of (A) 0.2, 0.5 and 1.0 µg/L, respectively; and (B) 2.0, 5.0 and 10 µg/L. Linearity and Detection Limits Figure 4 shows an overlay of chromatograms of the serial standard solutions of carbamates. Calibration linearity for the determination of carbamates by this method was investigated by making replicate injections (n = 7) of serial standard solutions of carbamates at six different concentrations. Detection limits of carbamates were calculated by using the equation found in EPA 531.1 and 531.2: Detection limit = St (n – 1, 1 - α = 0.99) Where: S = standard deviation of replicate analyses t (n – 1, 1 - α = 0.99) = Student’s value for the 99% confidence level with n -1 degrees of freedom, n = number of replicates 7 8 7 8 10 11 11 Carbamates Aldicarb sulfoxide Aldicarb sulfone Oxamyl Methomyl 3-Hydroxycarbofuran Aldicarb Propoxur Carbofuran Carbaryl Methiocarb Table 3: Method linearity data and method detection limits (MDL) Correlation coefficient (R) * When n = 10, t (n – 1, 1 - α = 0.99) = 3.17 Carbamates Detected (µg/L) Aldicarb sulfoxide Aldicarb sulfone Oxamyl Methomyl 3-Hydroxycarbofuran Aldicarb Propoxur Carbofuran Carbaryl 1-Naphthol Methiocarb Method 531.1 MDL requirements (µg/L) Method 531.1 MDL (µg/L) Dionex Method MDL (µg/L) 0.9992 2.0 0.59 0.018 0.9995 2.0 1.00 0.046 0.9994 2.0 0.86 0.035 0.9995 0.5 0.29 0.028 0.9994 2.0 1.90 0.036 0.9995 1.0 0.22 0.032 0.9994 1.0 1.00 0.031 0.9993 1.5 0.52 0.059 0.9995 2.0 1.30 0.026 0.9993 4.0 1.90 0.041 Table 4: Tap water sample analysis Added 1 (µg/L) Found RSD Recovery (µg/L) (%) (%) Added 2 (µg/L) Found (µg/L) RSD Recovery (%) (%) 0.0 0.20 0.20 6.25 102 10.00 10.66 4.14 107 0.0 0.20 0.21 8.42 103 10.00 10.65 4.60 107 0.0 0.20 0.19 13.4 93 10.00 10.60 4.52 106 0.0 0.20 0.18 5.11 92 10.00 10.88 4.61 109 0.0 0.20 0.19 4.25 94 10.00 10.46 4.43 105 0.0 0.20 0.18 6.16 88 10.00 10.88 4.30 109 0.0 0.20 0.19 6.92 92 10.00 10.56 4.67 106 0.0 0.20 0.21 8.11 103 10.00 10.60 4.78 106 0.0 0.20 0.17 6.28 87 10.00 10.54 4.85 105 0.0 0.20 0.20 4.47 99 10.00 10.22 4.52 102 0.0 0.20 0.20 4.82 100 10.00 10.46 4.80 105 Ten replicate injections of reagent water fortified with 0.2 µg/L carbamate standard were used in this method. Table 3 summarizes the data, which show excellent method linearity and sensitivity, with detection limits well below those defined in the EPA method. (The improved detection limits are largely due to improvements in fluorescence detector sensitivity and reversed-phase column technology since the original EPA work was completed. The EPA method used a 5 µm 4.6 x 250 mm column while this method used a 3 µm 4.6 x 150 mm column to yield more efficient peaks.) These improved limits easily allow the analyst to reach the minimum reporting limits (3-5 times the MDL) of the original method. Application Note 96 5
Page 1 and 2: Determination of N-Methylcarbamates
Page 3: Place 2.32 g potassium dihydrogen c
Page 7: CONCLUSION This application note de

AN96: Determination of N-Methylcarbamates by Reversed ... - Dionex

Create successful ePaper yourself

Delete template?

Save as template?