The determination of residual solvents in pharmaceuticals using the Agilent G1888 headspace/6890n GC/5975 inert MSD system Application Note

Transcription

1 The determination of residual solvents in pharmaceuticals using the Agilent G1888 headspace/6890n GC/5975 inert MSD system Application Note Roger L. Firor Albert E. Gudat Abstract The Agilent G1888 network headspace sampler (HS) interfaced to an Agilent 6890N gas chromatograph (GC) and configured with an Agilent 5975 inert mass-selective detector (MSD) were used for the determination of regulated residual solvents. Standard mixtures in water were used at various concentrations including levels at or below published acceptance guidelines to demonstrate system performance. Solvents in class 1 and class 2 according to ICH guidelines (including those listed in USP 467) were included. The MSD was operated in synchronous SIM/scan mode to collect both selected ion monitoring (SIM) and scan data for compound quantitation and identification, respectively. Method detection limits (MDLs) for 27 solvents were determined.

2 Introduction Organic volatile impurities (OVIs) can result from the manufacture of active pharmaceuticals, excipients, or other drug products. Many can be used to enhance yields, improve crystallization or increase solubility 1. Other factors such as packaging, transportation, and storage can also impact the level of residual solvents. Gas chromatography coupled with static headspace sampling is acknowledged as an easy-to-use high-throughput analytical tool for the determination of low level solvent impurities in drugs and can be found in nearly all QC laboratories in pharmaceutical manufacturing. Sample prep is relatively simple, and the methology is easily validated as per specific monographs. General guidelines established by the International Conference on Harmonization (ICH) divide solvents into three classes 2. Class 1 solvents should not be used in manufacture because of toxicity or environmental impact while class 2 solvent use should be limited due to potential toxicity. Solvents regarded as posing a lower risk to human health are class 3. Solvents listed in USP 467 include a subset of specific class 1 and class 2 solvents. This work will demonstrate the analysis and quantitation of class 1 and 2 solvents. See table 1A-C for a listing of residual solvents. Residual solvent and other contaminant levels designated as safe have trended downward in recent years as information about potential harmful effects of long-term and/or low-level exposures accumulate and as the detection sensitivity of analytical instrumentation Solvent Concentration limit (ppm) Concern Benzene 2 Carcinogen Carbon tetrachloride 4 Toxic and environmental hazard 1,2-dichloroethane 5 Toxic 1,1-dichloroethene 8 Toxic 1,1,1-trichloroethane 1,500 (revised 10 ppm) Environmental hazard Table 1A Class 1 solvents in pharmaceutical products (solvents that should be avoided) 2. Solvent PDE (mg/day) Concentration limit (ppm) Acetonitrile Chlorobenzene Chloroform Cyclohexane ,880 Cis 1,2-dichloroethene ,870 Dichloromethane ,2-dimethoxyethane N,N-dimethylacetamide ,090 N,N-dimethylformamide ,4-dioxane ethoxyethanol Ethyleneglycol Formamide Hexane Methanol ,000 2-methoxyethanol Methylbutyl ketone Methylcyclohexane ,180 N-methylpyrrolidone ,840 Nitromethane Pyridine Sulfolane Tetralin Toluene ,1,2-trichloroethene Xylene ,170 1 Usually 60% m-xylene, 14% p-xylene, 9% o-xylene with 17% ethyl benzene Table 1B Class 2 solvents in pharmaceutical products 2 (PDE = personal daily exposure). Solvent Table 1C Solvents in pharmaceutical products according to USP 467 Method IV. Concentration limit (ppm) Methylene chloride 600 Chloroform 60 Benzene 2 Trichloroethylene 80 1,4-dioxane 380 improves. For example, based on new toxicity data, a 2003 change in the regulations for residual solvents stipulate a ten-fold reduction of the 1997 PDE (personal daily exposure) and residual concentration limits for the solvent N- methylpyrrolidone 3. It also reclas- 2

3 sifies tetrahydrofuran from a class 3 to a class 2 category solvent with PDE and concentration limitations more restrictive than toluene. Table 1A-B lists current PDE and concentration limits for class 1 and class 2 residual solvents in pharmaceutical products 4. Experimental The HS/GC/MSD system described in this work provided for compound identification, confirmation and quantitation of resolved or coeluting peaks. 10-mL headspace vials with teflon seal caps were used containing 5 ml water as the matrix with 3 grams sodium sulfate added. The headspace sampler was equipped with a 1-mL sample loop. Sufficient flow must be maintained through the system to avoid excessive peak broadening, therefore split injection is used. At the chosen split ration of 5:1, the headspace sample loop is swept fast enough to produce good peak shapes. A mass spectral quantitation database was set up manually by identifying unique ions for each solvent and selecting quantitation by target ions. The AutoSIM setup program in the data analysis software (version D.02.00) was applied, resulting in 16 SIM groups for the 27 analytes in the sample. 7 This automated setup processes full scan data into SIM acquisition parameters. A new SIM/Scan method was then saved with the automatically generated SIM timetable incorporated. These groups are shown in figure 1. Figure 1 Output from the AutoSIM setup used to generate the time-programmed SIM groups and dwell times of the ions to be monitored. 6890N GC Injection port Volatiles interface Temperature 160 C Split ratio 5 : 1 Carrier gas Helium Carrier flow 1.5 ml/min GC oven program Initial temperature 35 C Initial time 20 min. Rate 25 C/min. Final temperature 250 C Final time 10 min Columns 30 m x 0.25 mm x 1.4 µm DB-624, part# G1888A headspace sampler Loop size 1 ml Vial pressure 12.0 psig Headspace oven 85 C Loop temperature 100 C Transfer line temperature 120 C Equilibration time 30 min., high shake GC cycle time 50 min. Pressurization 0.15 min. Vent (loop fill) 0.2 min. Inject 0.5 min inert MSD Synchronous SIM/scan mode on SIM 16 groups for 27 analytes Scan 30 to 200 amu, samples 2 1 Threshold 75 Source temperature 230 C Quad temperature 150 C Tune atune.u ChemStation software G1701DA D Standards USP 467 Restek #36007 ICH class 1 and 2 Restek #36261 (class 1 revised) #36229 (class 2A) #36230 (class 2B) 3

4 Results and discussion Most quality control labs in pharmaceutical manufacturing employ gas chromatography for the determination of residual solvents that are included in either USP 467 or the more extensive list covered in ICH guidelines. Capillary gas chromatography based on the 624 phase (USP G43) is widely used for separation. A different stationary phase such as DB-1701 or DB-5 can be utilized in specific methods when coelution has been identified. However, coelution is usually not a problem with mass spectrometric detection when the coeluting compounds each have unique ions. Headspace sampling has many advantages over direct liquid injection including the avoidance of large water injections that can result in column degradation and coelution. Headspace equilibration time is normally set at 60 minutes as specified in USP 467, however, in most cases 30 minutes is sufficient when operating at 85 C equilibration temperature. 5 Instead of adding the USP specified 1 gram of sodium sulfate to the 10-mL headspace vial containing 5 ml of water, 3 grams of sodium sulfate was added to ensure super saturation at 85 C and to force the maximum analyte concentration into the headspace. Table 2 lists concentrations and identifications of class 1 and class 2 solvents used to produce the sim/scan chromatograms shown in figure 3. These concentrations equal the guideline limits based on a 100 mg sample of the pharmaceutical or excipient dissolved in 5 ml A B scan 45 to 555 amu SIM 4 ions, 40 ms scan 45 to 555 amu SIM 11 ions, 40 ms amu/s amu/s amu/s amu/s amu/s amu/s 3.8 cycle/s Same width (SIM) a cycle 2.9 cycle/s 1.9 cycle/s 1.9 cycle/s Same width (SIM) 1.6 cycle/s 1.3 cycle/s 1 sec 2 sec 1 sec 2 sec Figure 2 A) SIM/Scan operation with selected sampling rates for 4-ion group, 40 ms dwell. B) SIM/Scan operation with selected sampling rates for 11-ion group, 40 ms dwell Figure 3 Class 1 and Class 2 residual solvents acquired in synchronous SIM/scan mode for concentration given in tables 1A-B. 4

5 water. Concentrations used throughout this work are defined as the equivalent concentration of a solvent in the excipient (ppm) placed into the headspace vial. Figure 4 gives the chromatograms for the USP 467 solvents at 1/10th the limit concentration. Figure 5 illustrates the resolution and SIM sensitivity realized for benzene and 1,2-dichloroethane at low concentrations. Calibration curves for SIM data of a few solvents including those from the USP 467 method are shown in figure 6. Linear results are seen over a concentration range that extends well below recommended maximum concentrations. The curves for methylene chloride and o-xylene are included to illustrate the effect of detector saturation during the elution of giant-size peaks even though big electron multiplier voltage de-creases were scheduled (figure 7). The effect of such a voltage reduction can be seen in figure 4 as the signal appears to drop to near zero at around 7 and 14 minutes. The synchronous SIM/Scan mode of acquisition provides for collection of both SIM data and full scan data in a single run. See figures 2a and 2b for an example graphical representation of the SIM/Scan data acquisition approach used for 4 and 11 ion groups, respectively. 8 Note the time spent on SIM is the same regardless of sampling rate. The time spent on scan will vary depending on sampling rate setting. Chromatograms from a synchronous SIM/Scan acquisition of class 1 and class 2 solvents at the 4 TIC: 10UL USP MIX#5.D\data.ms 7 Scan Data TIC: 10UL USP MIX#5.D\datasim.ms SIM Data Figure 4 USP 467 residual solvents at 1/10th the limit concentrations: 1. Methylene chloride 60 ppm, 2. Chloroform 6 ppm, 3. Benzene 0.2 ppm, 4. Trichloroethylene 8 ppm, 5. 1,4-dioxane 38 ppm TIC: 5 UL STD.D\DATASIM.MS TIC: 10 UL STD.D\DATASIM.MS TIC: 50 UL STD.D\DATASIM.MS TIC: 100 UL STD.D\DATASIM.MS Benzene Limit concentration Figure 5 Resolution and sensitivity for benzene and 1,2-dichloroethane. 1,2-dichloroethane 1/2 limit conc. 1/10 limit conc. 1/20 limit conc. 5

6 limit excipient concentrations from table 2 are shown in figure 3. Method detection limits (MDLs) for SIM data are given in table 2. MDLs were calculated as specified in the US EPA Method Seven headspace vials containing class 1 and 2 solvents at 1/10th the limit excipient concentration (table 3) were prepared and analyzed. The formula in table 3 was then used to calculate the MDLs for all target compounds. Given the somewhat limited dynamic range of the MSD and the large range of limit concentrations for the analytes (from a low of 2 ppm for benzene to a high of 4840 ppm for N-methylpyrrolidone), time programmed changes to the electron multiplier voltage (EM) were necessary to keep the very large peaks from saturating the electronics and still achieve meaningful areas for the smaller peaks. Since chromatograms usually show additional peaks from sources other than those coming from the target compounds, spectra obtained from the scan data can very effectively be used for unknown identification by library searches or manual interpretation. Such was the case also with the standard analyzed in this work. One large peak at minutes did not belong to the list of targets. Library search of the spectrum identified the peak as Dimethylsulfoxide (DMSO). This was not surprising since DMSO was the solvent used for the preparation of the standards. However, other extraneous peaks could just as easily be identified from the full spectrum. This is one of the great advantages of doing synchronous SIM/Scan data acquisition where the SIM data is used for sensitive and reproducible quantitation while the scan data is 6 Solvent ( #), t R (min) MDL(ppm) Solvent (#), t R (min) MDL (ppm) Methanol ( 1) Trichloroethylene (14) ,1-dichloroethene ( 2) Methyl cyclohexane (15) Acetonitrile ( 3) ,4-dioxane (16) Methylene chloride ( 4) Pyridine (17) Hexane ( 5) Toluene (18) Cis 1,2-dichloroethene ( 6) hexanone (19) Chloroform ( 7) Chlorobenzene (20) Carbon tetrachloride ( 8) Ethylbenzene (21) Cyclohexane ( 9) N,N-dimethylformamide (22) ,1,1-trichloroethane (10) m-xylene* (23) Benzene (11) p-xylene* (24) ,2-dichloroethane (12) o-xylene (25) ,2-dimethoxyethane (13) N,N-dimethylacetamide (26) ,2,3,4-tetrahydronaphthalene (27) *Coeluting peaks on DB 624 column with no unique and differentiating ms ions. Table 2 Class 1 and class 2 residual solvent method detection limits (MDL) and retention times (t R ). MDL = s t (n-1, 1-alpha=99) = s Where: t (n-1, 1-alpha=99) = Student s t value for the 99 % confidence level n with n-1 degrees of freedom = number of trials Table 3 Formula for MDL calculations from EPA Method Figure 6 Calibration plots for USP 467 solvents and ortho-xylene.

7 used for unknown identification. The Agilent implementation allows collection of both SIM and scan data in a very narrow cycle time. 8 The SIM masses used for identification and quantitation of the solvents in the work are listed in table 4. Conclusions Manufacturers of pharmaceuticals must ensure that residual solvents (organic volatile impurities or OVIs) and related contaminants are not present in their products or are present below levels stipulated as safe by regulation. One of the impediments to accurate determination of impurities at very low levels is the proclivity for analyte interaction and/or reaction with the internal surfaces of the instrument sample path. To eliminate this problem, a new inert G1888 headspace sampler was developed. Carryover, a common concern in older headspace samplers is also greatly reduced. 5 The whole system has a non-reactive, non-adsorptive sample flow path from the point of injection through detection. When coupled to the 5975 inert MSD which utilizes a solid inert source superior results are obtained when the need for unknown identification, confirmation, and quantitation is required. Analytical results obtained from the inert HS/GC/5975 MSD provides excellent sensitivity when utilizing SIM/Scan data aquisition. This feature of the 5975 MSD allows for very low level detection and quantitation of target ions while also searching for unknowns using scan. Confirmation is still possible since library searchable full scan data is collected along with SIM data for best sensitivity. This feature is made possible in Quant Q1 Q2 Name Methanol ,1-dichloroethene Acetonitrile Methylene chloride ,2-dichloroethene Hexane Cis 1,2-dichloroethene Chloroform ,1,1-trichloroethane Cyclohexane Carbon tetrachloride Benzene ,2-dichloroethane ,2-dimethyoxyethane Trichloroethylene Methylcyclohexane ,4-dioxane Pyridine Toluene Hexanone N,N-dimethylformamide Chlorobenzene Ethylbenzene m- & p-xylene o-xylene N,N-dimethyacetamide ,2,3,4-tetrahydronaphthalene Table 4 SIM masses used for quantitation of the analyzed solvents. Quant target = ion used for identification and quantitation, Q1, Q2 = qualifier ions used for identification. Figure 7 Run time table for changes to the electron multiplier voltage. the Agilent 5975 without a compromise in performance by use of performance or fast electronics. 8 The methods and procedures outlined in this work illustrate new potential approaches to the analysis of residual solvents. The ChemStation software used is the G1701DA MSD Productivity ChemStation (version D.02.00). For regulated laboratories the MSD Security ChemStation (G1732AA) provides the ability to work in full compliance with 21 CFR Part Before transferring methods into routine use laborato- 7

8 ries should validate their methods according to the respective guidelines published by industrial committees and regulatory agencies, such as the ICH (International Conference on Harmonization), USP (United States Pharmacopeia) or EP (European Pharmacopeia). Methods developed and validated with the system described in this Application Note can then be used in quality control with the MSD Security ChemStation. References 1. Anil M. Dwivedi, Residual Solvent Analysis in Pharmaceuticals, Pharmaceutical Technology, 42-46, Nov Guidance for Industry, Q3C Impurities: Residual Solvents, U.S. Department of Heath and Human Services, FDA, Center for Drug Evaluation and Research (CDER), Center for Biologics Evaluation and Research (CBER), ICH, Dec Revised PDEs for NMP and THF, Federal Register, 68, (219), Notices, 64353, Nov Limits of Residual Solvents, Federal Register, 62, (247), Notices , Dec Roger L. Firor, The Determination of Residual Solvents in Pharmaceuticals Using the Agilent G1888 Network Headspace Sampler, Agilent Technologies Application Note, publication number EN, June US EPA Method 524.2, Measurement of Purgeable Organic Compounds in Water by Capillary Column Gas Chromatography/Mass Spectrometry, Revision 4, Aug Harry Prest and David W. Peterson, New Approaches to the Development of GC/MS Selected Ion Monitoring Acquisition and Quantitation Methods, Agilent Technologies Application Note, publication number EN, Nov Chin-Kai Meng, Improving Productivity with Synchronous SIM/Scan, Agilent Technologies Application Note, publication number EN, May Agilent MSD Security ChemStation for GC/MS Systems, Specifications, publication number EN, Jan Roger L. Firor and Albert E. Gudat are Application Chemists at Agilent Technologies, Inc. Paramus, NJ, USA. Copyright 2005 Agilent Technologies All Rights Reserved. Reproduction, adaptation or translation without prior written permission is prohibited, except as allowed under the copyright laws. Published June 1, 2005 Publication Number EN