Environmental Parallel Evaporation Guide EPA Compliant Solvent Concentration

Transcription

1 Environmental Parallel Evaporation Guide EPA Compliant Solvent Concentration

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3 Contents This environmental parallel evaporation guide describes important aspects of the simultaneous concentration of multiple samples to a pre-defined residual volume using the parallel evaporator equipped with a Solvent Vapor Recovery system with integrated control (SVR-N), Syncore Analyst. Guidelines for the concentration of specific solvents and solvent mixtures complying with US EPA methods are presented. They will help to streamline the own process with sample applications, checklists, hints, rules, tables and tests. Further information about applications can be found on our website, in BUCHI Application Notes and best@buchi publications. The local BUCHI representative can be contacted for additional information on a particular application. 1 Introduction 5 SECTION I Syncore SYSTEM 2 Configurations Syncore Analyst Syncore solid phase extraction (SPE) advanced module Recommended accessories Vacuum Pump V-700, Vacuum Controller V-855 and Recirculating Chiller F-108 / F Sample vessels with appendix Flushback module Cooled receiving vessel Syncore Analyst appendix sleeve Rubber plugs Sample vessel holder Example set-up 14 3 Process checklist 17 4 Parameters, settings and their impact on the concentration process Instrument configuration Initial solvent volume Temperatures the ΔT 25/20 C rule Vacuum cover temperature Vacuum and boiling point How to determine the vacuum for a given boiling point by manual distillation How to determine a pressure gradient for distillation Heat and heat transfer medium Rotational speed Solvent mixtures End of process 25

4 SECTION I Syncore SYSTEM 5 Further use of recovered solvents 27 6 Troubleshooting Leakage Inhomogeneous concentration Insufficient solvent recovery rate Re-condensation in sample vessels with appendix Contamination and low analyte recovery rate 33 7 Applications Concentration according to US EPA Methods Overview of US EPA Methods using the Syncore technology 35 SECTION II COMPLIANCE WITH US EPA METHODS 8 Applications Concentration of selected solvents Acetonitrile Dichloromethane Dichloromethane : Acetone (80 : 20 vol%) Diethyl ether n-hexane n-hexane : Acetone (80 : 20 vol%) 43 9 Case study: SPE application for the determination of PAH in water Introduction Experimental Results Conclusion Appendix Solvent table and classification Boiling point calculation as a function of the applied pressure Pressure Boiling point and temperature table List of Syncore systems, accessories and spare parts References 55

5 5 1 Introduction Over the last decades, our environment has been contaminated by several pollutants contained as by-products of processes and materials enabling our modern lifestyle. Some examples are presented in Table 1.1. Table 1.1. Examples of environmental pollutants Pollutants Chlorinated herbicides and pesticides Polychlorinated biphenyls (PCBs) Polybrominated diphenyl ethers (PBDEs) Total petroleum hydrocarbons (TPH) mineral oil saturated hydrocarbons (MOSH) mineral oil aromatic hydrocarbons (MOAH) polycyclic aromatic hydrocarbons (PAHs) Usage / source Agriculture Flame retardants, additives in plastics and in many more applications until the 1980s Substances made from crude oil; released to the environment during partial combustion of organic matter and/or recycling processes These pollutants tend to accumulate in sediment and soil, and are also found in water and air probes. Due to health concerns, laboratories around the world are analyzing pollutant levels in the environment. Such environmental soil, water, air and waste samples are usually extracted with an organic solvent which is subsequently concentrated before final analysis to overcome detection limits. During the concentration step, traditionally performed by Kuderna-Danish (KD) or nitrogen blow-down devices, organic solvent fumes can escape to the environment. Thus, condensation of solvent vapors is inefficient, if applied at all. These solvent vapors are harmful to exposed operators and persist in the atmosphere where they may also accelerate global warming. Obviously, environmental laboratories play a pioneering role in benign use and recycling of organic solvents. Therefore, they are strictly controlled. Special attention is paid to chlorinated solvent emission. Dichloromethane, for example, has a high global warming potential and is considered as possibly carcinogenic to humans.[1] High solvent emissions and non-compliance with most Environmental Protection Agency (EPA), such as the US EPA, regulations will lead to severe monetary fines.[2] Here, the Syncore technology applied in automated parallel concentration of samples and recovery of organic solvents is presented. Table 1.2 shows some benefits of the Syncore system compared to the traditional KD. Selected US EPA applications are listed in chapter 7 where the Syncore Analyst has been proven to be a working horse for the environmental laboratories. The aim of this environmental parallel evaporation is to provide tips and tricks for optimizing existing concentration processes and to assist the Syncore user in developing new applications in environmental analysis.

6 6 Table 1.2. Comparison of the Kuderna-Danish and the Syncore Analyst technology Kuderna-Danish (KD) Work intensive Syncore Analyst Completely automated manual process requiring a user present at all times programmed slope or step-down vacuum setting and chilled appendix technology requires no user interaction Low reproducibility High reproducibility no ability to stop at a set residual volume high probability of cross-contamination chilled appendix technology consistently concentrates samples to the same final volume individual sealing system eliminates crosscontamination Unsafe practices > 95 % solvent recovery harmful emissions due to the lack of a solvent recovery system pre- and post-pump solvent recovery condensation units

7 SECTION I Syncore SYSTEM 7 2 Configurations Common to all Syncore configurations is the platform (Figure 2.1, left). The platform performs an orbital movement with a maximum speed of 300 rpm at programmable temperatures up to 100 C,[3] producing a strong vortex in the sample vessels. This is ideal for fast solvent concentrations. Figure 2.1. Left: Syncore platform. Right: available Syncore Analyst racks (R-4 and R-6: Crystal rack, R-12: aluminum rack). Based on the unique chilled appendix technology in the Syncore Analyst configuration (Figure 2.1, right), the solvent can be concentrated to a pre-defined residual volume, suitable for sample preparation, e.g., prior to GC/MS analysis. Also, a special cover plate can be used for solid phase extraction, SPE, a method often applied for further purification of environmental samples. In this chapter, the Syncore Analyst with focus on environmental sample preparation is described in detail. The available Syncore configurations for an automated concentration and the corresponding working sample volumes are listed in Table 2.1. Table 2.1. Available Syncore Analyst and SPE configurations Sample positions Working volume [ml] Appendix [ml] , 1, , 1, , 1, Syncore Analyst The Analyst configuration is designed to simultaneously concentrate up to 12 samples with working volumes of ml down to pre-defined residual volumes of 0.3, 1 or 3 ml, typical volumes needed for, e.g., GC/MS. A key feature of the Analyst is an integrated cooling zone that maintains the concentrated sample in a chilled appendix (Figure 2.2).[4] The chilled zone is cooled by a cooling medium from a recirculating chiller and helps to efficiently retain a predefined sample volume in the Analyst sample vessel appendix over a longer period of time avoiding evaporation

8 8 SECTION I Syncore SYSTEM to dryness. The cooling temperature selected for the sample vessel appendix and the vacuum applied must be synchronized for optimal concentration conditions. The Analyst configuration is predominantly applied in environmental analysis, food analysis and quality control where the concentration of an extract is generally required prior to further analytical steps. pre-defined residual volume hot cold hot cooling medium Figure 2.2. Analyst rack cools the appendix of the sample vessel avoiding evaporation to dryness. 2.2 Syncore solid phase extraction (SPE) advanced module In SPE, a liquid sample is passed over a so-called stationary phase. According to the affinity of the substances in the sample for the stationary phase, they either pass over or are retained. In case the fraction that passes the stationary phase contains the desired substance, it is collected in the sample vessels with appendix; otherwise it is discarded. Analytes that adhere to the stationary phase can subsequently be washed from residual matrix material and eluted from the stationary phase for collection with an appropriate eluent. SPE can easily be performed with the Syncore Analyst by installing an SPE advanced cover, or by converting the vacuum cover with the SPE advanced module, accommodating 6 or 12 cartridge ports according to the corresponding Analyst racks (Figure 2.3). Unique feature of this set-up is a three-way valve which allows liquid separation into either a waste vessel or a collection vessel after passing through an SPE cartridge (Figure 2.4).[4] This makes it possible to first transfer the liquids of the conditioning, adsorption and washing steps into the waste vessel, and then to elute directly into the concentration vessel. No exchange of glassware or aeration whatsoever of the vacuum manifold is required. All essential SPE work-up steps can be performed without any liquid handling in-between. Moreover, by turning the valve into the stop position, the eluate can directly be concentrated to a pre-defined residual volume. Typical SPE applications comprise environmental and foodstuff analysis, see chapter 9.[5]

9 SECTION I Syncore SYSTEM 9 Figure 2.3. SPE advanced cover compatible with the R-12 Analyst rack SPE cartridge three-way valve waste stop waste waste elute elute elute vacuum cover sealing system sample vessel with residual volume rack hot cold residual volume cooling medium waste position: Cartridge is conditioned, loaded with the analyte and washed. stop position: Each sample can be stopped individually, to prepare the cartridge for the next step or to close the system for evaporation. elute position: Analyte is eluted directly into the sample vessel, where the sample is then concentrated to a pre-defined residual volume.

10 10 SECTION I Syncore SYSTEM 2.3 Recommended accessories Vacuum Pump V-700, Vacuum Controller V-855 and Recirculating Chiller F-108 / F-114 A prerequisite for a smooth concentration process is the control of the vacuum. The combination of a BUCHI Vacuum Pump V-700 with Woulff bottle and post-pump secondary condenser together with a BUCHI Vacuum Controller V-855 (Figure 2.5) is designed to be used with the Syncore. With this combination, pressure gradients can be programmed to ensure efficient, smooth, and reproducible concentrations. Constant cooling of the Syncore condenser, appendix, Flushback module and cooled receiving vessel is achieved with a BUCHI Recirculating Chiller F-108 / F-114 (Figure 2.6) which is also controlled by the BUCHI Vacuum Controller V-855. Figure 2.5. BUCHI Vacuum Pump V-700 with a post-pump secondary condenser and Woulff bottle equipped with a BUCHI Vacuum Controller V-855. Figure 2.6. BUCHI Recirculating Chiller F-108 with 800 W and F-114 with 1400 W cooling capacity at 15 C. Low temperature cooling allows gentle distillation under mild conditions (ΔT 25/20 C rule, chapter 4.3) required for temperature-sensitive compounds. Simultanaeously, with the combination of pre- and post-pump condensers together with a cooled receiving vessel, high solvent recovery is provided yielding an environmentally benign process, with almost no solvent emission to the atmosphere (> 95 % solvent recovery) Sample vessels with appendix Special sample vessels with an appendix volume of 0.3, 1 or 3 ml are available for all Analyst configurations (R-4, R-6, and R-12). These sample vessels are available with (Figure 2.7) graduation marks for respective volumns. Using these sample vessels, the sample can be concentrated to the pre-defined residual volume. Because of the chilled appendix, the residual volume remains stable for hours.

11 SECTION I Syncore SYSTEM 11 Figure 2.7. Analyst sample vessels with different graduated appendix sizes. The advantage of using BUCHI Syncore sample vessels with appendix is expressed in a more uniform concentration and higher recoveries. This is due to the narrow tolerances in height, diameter and wall thickness. The precise height of the sample vessels not only supports a leak tight system, it also prevents the sealing discs and the threaded rack bar from excessive damage due to an easier and gentler closing of the vacuum cover. The stability of the sample vessels enables cleaning in the dishwasher and autoclave which ensures contamination-free working while saving time and running costs. The use of BUCHI Syncore sample vessels with appendix guarantees fast, safe and reproducible concentration results. The concentration parameters in chapter 8 are exclusively valid and optimized for a Syncore Analyst system with geniune BUCHI glassware Flushback module Both the R-6 and R-12 Analyst configurations are optionally equipped with a Flushback module (shown in Figure 2.8 for the R-12 configuration). The module is placed on the rack and connected to a cooling source. With this unique feature, the top of each vessel is cooled where, the vaporized solvent partially condenses as it leaves the sample vessel, causing a gentle continuous rinse of the sample vessel wall during the entire concentration process. This ensures that the dissolved sample remains at the bottom of the vessel and in the chilled appendix, and adheres less to the sample vessel wall. It has been demonstrated (Figure 2.9) that the Flushback module significantly enhances the analyte recovery rate, in particular for analytes with a high affinity for glass. Also, by continuously rinsing the vessel wall, higher rotational speed is possible which allows low-boiling analytes to disperse better in the solution. Figure 2.8. Flushback module for an R-12 configuration.

12 12 SECTION I Syncore SYSTEM We suggest cooling the Flushback module before starting the concentration process. Usually, the Flushback module is cooled by the same cooling source as the appendix and the condenser. Consequently, the drawback of the Flushback effect is a slight decrease in the concentration speed;[6] the better the Flushback effect, the slower the concentration process. Thus, the use of a Flushback module is ascribed to the question whether speed or analyte recovery is preferred. However, the use of a Flushback module makes an after-run rinsing unnecessary which at once saves time and extra solvent. cooling zone H 2 O out H 2 O in cooling zone heating zone residual volume H 2 O out H 2 O in Figure 2.9. Effect of the Flushback module. Left vessel: when using the Flushback module, the analyte is collected in the appendix. Right vessel: without using the Flushback module some analyte adheres more to the sample vessel wall. Schematic: operation principle of the Flushback module. H 2 O indicates the cooling medium Cooled receiving vessel When concentrating samples dissolved in low-boiling solvents having boiling points close to room temperature, e.g., dichloromethane, or samples dissolved in solvent mixtures, it is suggested to cool the receiving flask in an ice bath to prevent the recovered low-boiling solvent from re-evaporating and being released to the environment through the pump. A more elegant solution to this problem is the use of a cooled receiving vessel (Figure 2.10) which is cooled by the same cooling source as the rest of the Syncore system. The collected solvent can then easily be siphoned into the waste or for further use via the valve at the bottom of the vessel. Figure Cooled receiving vessel.

13 SECTION I Syncore SYSTEM Syncore Analyst appendix sleeve To protect the fluid remaining in the appendix from heating up and evaporating to dryness, a sleeve is inserted into each Analyst position (Figure 2.11). With this appendix sleeve, the sample remains in the appendix even when the platform continues to heat. This sleeve is available for the appendix sizes of 0.3 ml (transparent) and 1 ml (red), and is included with the corresponding sample vessel set. For the 3 ml appendix there is no need for an additional sleeve since it perfectly fits into the shaped cavity of the rack position. Figure Syncore Analyst appendix sleeve for sample vessels. Red: for 1 ml appendix. Transparent: for 0.3 ml appendix Rubber plugs When using a specific Analyst rack and not all positions contain samples, it is recommended to put the empty sample vessels in the rack positions anyway to allow the vacuum cover to tighten the system by a symmetric and even pressure on the vessels. For this reason, it is also important that the used sample vessels have the exactly same height. To prevent the condensation of solvent into the chilled appendix of the empty sample vessels, due to the cold trap effect, it is useful to seal the corresponding openings of the vacuum cover with a rubber plug (Figure 2.12). This also results in a quicker concentration across the filled positions. Figure Rubber plugs for empty sample vessel positions.

14 14 SECTION I Syncore SYSTEM Sample vessel holder For better handling of the sample vessels during preparation before concentration, and faster cooling of the probes after concentration, stainless steel holders for each sample vessel size (R-4, R-6 and R-12) are available (Figure 2.13). Figure Holder for R-4, R-6 and R-12 sample vessels. 2.4 Example set-up The schematic set-up of a BUCHI Syncore Analyst system with Flushback module including a BUCHI Vacuum Pump V-700 equipped with a BUCHI Vacuum Controller V-855 and a post-pump secondary condenser, a BUCHI Recirculating Chiller F-108 and a cooled receiving vessel is illustrated in Figure The sequential pathway of the cooling medium is shown in bluish color. Figure Schematic set-up of a Syncore Analyst system with Flushback module including a pump with post-pump secondary condenser, a recirculating chiller and a cooled receiving vessel. Bluish lines represent the sequential cooling medium loop; light blue is the coldest region which becomes more purple the more energy the cooling medium removes from the system.

15 SECTION I Syncore SYSTEM 15 To avoid back mixing of the condensed solvent in the vacuum tubing which is due to the big surface of the ribbed tubing exposed to room temperature, there should be a slight inclination of the vacuum tubing connecting the vacuum cover and the adapter to the condenser unit in order to let the condensate flow into the receiving vessel and not into the vacuum cover. It is suggested to always connect the cooled modules in a sequential way, preferably starting by the primary condenser followed by the appendix cooling, the Flushback module, the receiving vessel and the post-pump secondary condenser, to achieve best distillation performance with high solvent recovery (> 95 %). The cooling tubing should be kept as short as possible and, to avoid condensation or icing around the tubing when cooling at very low temperatures, the use of auxiliary insulation hoses is recommended. The quick connectors with cut-off function enable to change the modules of the Syncore system easily and without cooling medium leak when the loop is disconnected. By means of a flow indicator at the exit of the primary condenser, a consistent cooling medium flow can be monitored throughout the process.

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17 SECTION I Syncore SYSTEM 17 3 Process checklist In Table 3.1, a process checklist guiding the Syncore Analyst user through the concentration process is presented. The user can follow the checklist pointwise. For reproducible results, it is important to always follow the same procedure. Special attention needs to be paid on the rack pre-heating time, on the effective time at which the sample vessels are added into the rack, and on an immediate closing of the vacuum cover and start of the concentration process. Table 3.1. Syncore process checklist Process step Checkpoints Chapter Installation install Syncore platform according to operation manual Platform and cover preparation connect all accessories used according to operation manual check tap water/cooling medium and electricity choose configuration Analyst (R-4, R-6, R-12), SPE choose sample vessels 0.3, 1, 3 ml appendix with/without graduation mark use suitable appendix sleeve prepare samples separately with the aid of the sample holder fill in heat transfer medium (water for max. T rack = 80 C) in the rack cavities check tightness set concentration temperatures (ΔT 25/20 C rule) and press start pre-heat the rack and vacuum cover (30 min) 2.1, , Cooling parameters check if all cooled modules are properly connected to cooling loop set cooling medium temperature and press start on controller 4.3 Concentration parameters Concentration process set pressure gradient place Flushback module place the sample vessels previously prepared place rubber plugs at the empty position immediately close vacuum cover set vortex speed and start concentration control load of the condenser determine end of process stop procedure Cleaning cleaning procedure 6.6

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19 SECTION I Syncore SYSTEM 19 4 Parameters, settings and their impact on the concentration process 4.1 Instrument configuration Based on the number of samples and their volumes, different Syncore configurations can be chosen. It has to be kept in mind that concentration rates greatly differ depending on various parameters. A change in the rack size for the same sample volume, for example, can influence the concentration efficiency. Maximization of the surface-to-volume ratio by adjusting the rotational speed is therefore required (chapter 4.7). The use of a Flushback module increases the analyte recovery by gently rinsing the glass wall of the sample vessels. This, however, slightly lowers the evaporation rate (chapter 2.3.3). Which configuration best fits to ones need is thus dependent on what is more important, a fast concentration or high analyte recoveries. 4.2 Initial solvent volume For optimum concentration, it is advised to fill the vessel to no more than the maximum working volume (Table 2.1). If the sample vessels are excessively filled, no vortex can be produced by rotation, plus, the solution will come into contact with the sealing discs and the vacuum cover which may cause cross-contamination and/or carry-over. Both, the sealing discs and the vacuum cover, will need to be cleaned thoroughly to avoid carry-over (chapter 6.6) in such a case. 4.3 Temperatures the ΔT 25/20 C rule For optimum performance, the Syncore platform is pre-heated to the required temperature 30 minutes prior to starting the concentration. The maximum platform temperature is 100 C.[3] Simultaneously, the vacuum cover is pre-heated automatically by the platform. As a starting point to find the optimum temperatures for the rack, the boiling point, and the condensation temperature, a rule of thumb can be applied the ΔT 25/20 C rule. This rule specifies the temperature difference between the three different zones, i.e., the heating plate, the vapor temperature,[7] and the cooling temperature, as illustrated in Figure C 40 C When, for example, the temperature of the platform is set to 65 C, the vacuum should be set such that a boiling point of 40 C results, i.e., a ΔT of 25 C. The BUCHI Vacuum Controller V-855 allows to automatically determine the corresponding pressure (see chapter 4.4.2). In order to achieve sufficient condensation, the cooling temperature should be lower by at least another ΔT of 20 C. Hence, in this example 20 C. 65 C Figure 4.1. Illustration of the ΔT 25/20 C rule.

20 20 SECTION I Syncore SYSTEM The cooling medium for the condenser is also used to cool the appendix and the Flushback module. When applying the ΔT 25/20 C rule, the heating and cooling temperatures differ by 45 C which assures that the predefined Analyst residual volume remains in the appendix Vacuum cover temperature By default, the temperature of the vacuum cover is 50 C. Set the temperature of the vacuum cover to at least 5 C higher than the temperature of the solvent vapor (boiling point). A temperature of the vacuum cover lower than that of the solvent fumes causes the fumes to condense in the vacuum cover which may lead to crosscontamination. Maximum vacuum cover temperature is 70 C. Thus, a maximum vapor temperature of 65 C should not be exceeded to avoid condensation in the vacuum cover. The set temperature of the vacuum cover can be checked and adjusted by simultaneously pressing the UP and DOWN buttons on the temperature control unit of the Syncore platform. The display will then show, for example, P50 which means that the vacuum cover temperature is set to 50 C. The temperature can be changed with the UP and DOWN buttons according to the ΔT 25/20 C rule (cover should be set 5 C higher than vapor temperature). After few seconds, the display will show again the actual rack temperature. 4.4 Vacuum and boiling point Boiling is referred to as the state where the vapor pressure equals the pressure acting on the liquid s surface. Consequently, reducing this pressure by applying a vacuum lowers the boiling point of the solution. In other words, when applying a vacuum, it is possible to concentrate a solvent at lower temperature. These conditions allow a gentle concentration of temperature-sensitive compounds and a higher recovery of volatile analytes. In Figure 4.2, the pressure-dependent boiling point of pure water is illustrated. A decrease of the pressure from ambient to 120 mbar reduces the boiling point from 100 C to 50 C. A further pressure decrease to 42 mbar reduces the boiling point of water to 30 C. From Figure 4.2 it is obvious that at low pressures the boiling point may vary greatly with small pressure changes due to the logarithmic nature of the pressure curve (Equation 1 in chapter 10.2). Therefore, at low pressures, distillation has to be performed carefully to avoid boiling, bumping and foaming. This issue can be overcome by the use of a pressure gradient on the BUCHI Vacuum Controller V-855. After adequately decreasing the pressure (chapter 4.4.2) until the desired residual volume is reached, the system pressure is steadily increased from final vacuum to ambient conditions to avoid splashing of the sample and/or condensate. Furthermore, by activating the aeration function on the Vacuum Controller V-855 (menu options options controller aeration: ON), the system is completely aerated after the gradient has finished. This ensures that the residual volume remains constant. Temperature [ C] mbar, 50 C 42 mbar, 30 C Pressure [mbar] Figure 4.2. Pressure-dependent boiling point of pure water. Red point indicates the boiling point (bp) under ambient conditions (1 atm). The pressure-dependent boiling point curve can be calculated according to the equation in chapter 10.2.

21 SECTION I Syncore SYSTEM 21 Another measure to prevent bumping and foaming is by manually increasing the pressure and/or shortly aerating the system at constant temperature How to determine the vacuum for a given boiling point by manual distillation The most convenient way to control the applied vacuum is to use a BUCHI Vacuum Pump V-700 in combination with the BUCHI Vacuum Controller V-855. To determine the vacuum that has to be applied for given concentration conditions, follow these steps (Figure 4.1): 1. set the platform temperature, e.g., to 65 C 2. determine the pressure using the solvent library included in the BUCHI Vacuum Controller V-855 (or see chapter 10.3) so that a boiling point of, e.g., 40 C results (ΔT 25/20 C rule) 3. set the vacuum cover temperature at least 5 C higher than the boiling point, i.e., 45 C 4. set the cooling temperature 20 C lower than the expected boiling point, i.e., 20 C The as-found process can further be optimized individually How to determine a pressure gradient for distillation To avoid boiling, bumping, foaming or loss of analyte, the use of a pressure gradient programmed on the BUCHI Vacuum Controller V-855 is recommended. Besides, a programmed pressure gradient provides optimal preconditions for reproducible results. Any user can readily press one button and the exactly same concentration process starts. As a first approach for setting a gradient, the following procedure can be taken as a guideline (Figure 4.3): 1. determine the vapor temperature that should be achieved according to the ΔT 25/20 C rule and check the corresponding pressure needed on a solvent list (Table 10.2) 2. start 500 mbar above this calculated pressure 3. decrease the pressure by 350 mbar in 4 min 4. decrease the pressure further by 100 mbar in 5 min and another 50 mbar in 10 min 5. keep the pressure constant until the concentration is finished 6. for very volatile compounds, slow aeration to ambient pressure over 1-2 min is recommended Pressure [mbar] Time [min] Figure 4.3. Suggested pressure gradient for ethyl acetate (bp 77 C at ambient pressure) following the giving procedure.

22 22 SECTION I Syncore SYSTEM After a first assessment, optimization of the gradient is recommended to shorten the process time (see chapter 8). In case of unknown concentration conditions, e.g., solvent mixtures or solvents not included in Table 10.1, this is another procedure to follow: 1. start the Continuous Mode on the Vacuum Controller V-855 and lower the performance to 20 % 2. check the condenser load and switch to Manual Mode as soon as condensate is visible in the primary condenser 3. slowly decrease the pressure until the condenser load reaches the half height 4. write down the pressure settings and duration and program a pressure gradient to achieve reproducible results It is fundamental to check the performance with the pure solvent before concentrating samples with analytes to ensure that the chosen conditions are appropriate and high recoveries can be expected. 4.5 Condenser load For efficient vapor condensation, the temperature of the condenser should be at least 20 C (ΔT 25/20 C rule) lower than the vapor temperature, i.e., the boiling point. When concentrating at relatively low temperatures, i.e., rack temperature of approx. 50 C, a recirculating chiller is required to maintain the temperature. Whenever the condensate covers approximately half the height of the condenser, the concentration is optimal (Figure 4.4). Higher condenser loads usually have a negative impact on solvent recovery. To avoid possible emissions of solvent vapor through the pump into the environment, the use of a post-pump secondary condenser is highly recommended. As soon as no more condensation is observed in the condenser, the concentration process is finished. reduced pressure ½ ambient pressure Figure 4.4. Illustration of the optimum primary condenser load (half condenser height). Notice that the primary condenser condenses the solvent vapor at reduced pressure, the post-pump secondary condenser, on the contrary, works at ambient pressure.

23 SECTION I Syncore SYSTEM Heat and heat transfer medium Energy is needed to evaporate the solvents in the sample vessels. This energy is provided to the sample by heating the platform. For an efficient concentration, the applied heat has to be transported from the platform to the rack, from the rack to the glass sample vessel, and from the glass to the solvent. Small gaps filled with air between the platform and the rack, and between the rack and the sample vessel may significantly slow down the heat transfer to the sample. This is because air has a very low heat transfer coefficient compared to oil, water and aluminum. Thus, gaps between the platform and the rack can be filled by a very thin film of propylene glycol, or glycerine.[8] The gap between the rack and the sample vessels have to be filled with distilled or deionized water for an efficient heat transfer. Though, considering the boiling point of water as heat transfer medium, the maximum rack temperature to be set should not exceed 80 C to avoid the heat transfer medium to boil away. When using the R-4 or R-6 crystal racks, the amount of water to be added is indicated. For the R-12 rack, the gap between the heating block and the sample vessels should be completely filled. However, the heat transfer medium should be filled very carefully to prevent a dropping from the rack onto the platform or its control panel. It is further suggested to first fill the appendix cavity in the rack with distilled water and to fill up to the edge only after collocating the sample vessels. This avoids the appendix region to lack heat transfer medium due to air trapped under the appendix sleeve. Heat supplied to evaporate the solvent has to be removed by the condenser to liquefy the solvent again. When supplying more energy than the condenser can dissipate, the solvent is lost to the environment due to an overloaded condenser. Escaping solvent vapor may also condensate in the pump, reduce its efficiency and/or lead to damage. Furthermore, acceleration of the distillation through excess heat increases the risk of bumping and foaming as well as the loss of analyte with the vapor stream. Bumping and foaming can be avoided by reducing the heat supply and further measures (see chapter 4.4 and 4.8). 4.7 Rotational speed Generally, faster rotation increases the surface area, and hence, accelerates the concentration process. However, as shown in Figure 4.5, it also distributes the sample on a larger glass wall area which may reduce the analyte recovery. Better results in terms of analyte recovery are achieved by generating a smooth vortex with the lowest possible rotation. The use of a Flushback module not only further enhances the analyte recovery by gently rinsing the glass wall with re-condensed solvent, it also allows higher rotational speed for a better dispersion of more volatile compounds in the solvent.[9] Starting the vortex movement and applying the vacuum should be done immediately after placing the samples in the rack and closing the vacuum cover. Figure 4.5. Grease sticking to the glass wall of the Syncore sample vessels. Left: after concentration at 170 rpm. Right: after concentration at 300 rpm.

24 24 SECTION I Syncore SYSTEM With decreasing sample volume in the vessel during concentration, the sample temperature lowers due to the chilled appendix. Consequently, also the distillation is slowed down. To overcome this issue, the rotational speed can be increased leading to an enhanced vortex and a higher solvent surface in contact with the heated glass wall of the sample vessel. 4.8 Solvent mixtures Parallel concentration of solvent mixtures is often needed when the desired analytes could not be extracted from the sample efficiently enough by a pure solvent. Mixtures of solvents usually have evaporation properties different than their pure constituents. Evaporation tables of pure solvents can only give a first hint on the concentration conditions of solvent mixtures. Two solvents with a boiling point difference of more than 80 C can be separated by a single distillation which means that the lowerboiling solvent will evaporate first.[10] To prevent the low-boiling solvent from re-evaporating from the receiving vessel once the pressure is decreased further, the first fraction is disposed from the receiving vessel and the higher-boiling solvent is concentrated subsequently. Another solution to this problem is to cool the receiving vessel with an ice bath or use a cooled receiving vessel. Figure 4.6 illustrates an evaporation process of an ideal mixture of components X and Y. Starting from point 1, the solvent mixture of 50 % X and 50 % Y is heated up. At point 2a, the solution starts to evaporate. Interestingly, the composition of the vapor phase, 2b, is different from that of the liquid phase, 2a. In fractional distillation, different fractions of re-condensed vapor phases are collected. When using the Syncore, the re-condensed vapor is collected in the receiving vessel. With the progress of the evaporation, the compositions of the vapor and liquid phases change. In the liquid phase more and more X is found while the vapor phase contains more Y (point 3a and 3b). Finally, when everything is evaporated (indicated by points 4a/b and 5), the vapor composition which is condensed and collected in the receiving vessel equals the initial composition in the sample vessel. The solvent collected in the appendix when concentrating a solvent mixture consists of the solvent with the higher boiling point. If the dissolved components are not soluble in the higher-boiling solvent, they will precipitate in the appendix. high Temperature low 4a liquid phase 100 % X 0 % Y 3a 2a Figure 4.6. Evaporation of an ideal solvent mixture of 50 % X and 50 % Y. The progress and the composition of the mixture are indicated by red points (see text). 4b 1 5 Composition [%] 3b vapor phase 2b 100 % Y 0 % X

25 SECTION I Syncore SYSTEM 25 Usually, natural extracts tend to foam during the concentration process. Occasionally, this is due to compounds that precipitate and form a thin film at the liquid s surface. An approach to overcome this problem is by adding an extra solvent which is able to dissolve this precipitation. In case the extra solvent has a higher boiling point than the solution, a small amount is sufficient. Otherwise, an excess of lower-boiling extra solvent has to be added to ensure that some of it will prevent foaming until the concentration is over. Following this anti-foaming approach, it is important to keep in mind that the addition of an extra solvent may change the concentration performance. 4.9 End of process In general, concentration is finished when no more condensation is observed at the primary condenser. Therefore, the user has to optimize his process in regards of timing and settings. In this environmental parallel evaporation guide, to completely combat the chilled zone when using sample vessels with 1 ml residual volume, it is recommended to decrease the pressure by additional 50 mbar for roughly 3 minutes. In this way, an exact residual volume is achieved, i.e., 1 ml in this case.

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27 SECTION I Syncore SYSTEM 27 5 Further use of recovered solvents After being recovered, there are several options for the distilled and collected solvents. Due to its high calorific value and the low price the disposal of recovered hydrocarbon solvents as cement kiln fuel is an attractive disposal route. The high temperatures inside the cement kiln, the oxidizing atmosphere and the long residence times make it possible to cope with liquid residues, the disposal of which is often a problem in solvent recovery. Other processes making use of the heat derived from burning recovered solvents are the generation of steam in specially equipped boilers, the firing of lime kilns and the drying of road stone in coating plants. The environmental problems caused by chlorinated hydrocarbons emissions and legislative pressure has triggered their manufacturers to offer a recovery and disposal service for used materials.[11] Another option would be to sell the recovered solvents to other industries such as glue manufacturers who do not need high purity solvents; > 95 % purity is still fine. The further use of recovered solvents is thus dependent on their nature and properties. The amount used makes also a difference in the choice of the final disposal solution. Definitely, the recovered and collected solvents can be used as cheap cleaning solvents, especially when the analyte recoveries were shown to be high, and/or can be upgraded to higher purity for re-use by re-distillation. Any recycling solution will help to save money and, most importantly, to protect the environment.

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29 SECTION I Syncore SYSTEM 29 6 Troubleshooting 6.1 Overview On the one hand, an economic concentration process should be as fast as possible. However, a too fast concentration process could lead to foaming, bumping, solvent condensation in the vacuum cover as well as to lower analyte recoveries. On the other hand, a too slow concentration process that avoids the above problems can be very costly. Hence, there is a trade-off between fast and slow operation which asks for an optimum solution with highest possible analyte recoveries. Issues and their remedies encountered in optimizing the concentration process are listed in Table 6.1. Table 6.1. Solutions to the most frequent issues Problem Remedy Chapter Foam Overheating, bumping Condensation in cover / crosscontamination Slow concentration speed 1. increase pressure or shortly aerate 2. program/adjust gradient 1. increase pressure or shortly aerate 2. program/adjust gradient 3. reduce rack temperature 4. reduce time span from immersing the vessels into heat transfer medium to starting the orbital movement and the vacuum 1. increase cover temperature 2. reduce boiling temperature (reduce pressure) and adjust heat transfer medium as well as condenser temperature accordingly 3. ensure that the vacuum tubing has a slight drop between the vacuum connection and the adapter on the condenser unit 1. improve heat transfer (distilled water between rack and vessels) 2. optimize rotational speed 3. reduce pressure 4. increase platform/rack temperature

30 30 SECTION I Syncore SYSTEM Problem Remedy Chapter Inhomogeneous concentration Insufficient solvent recovery rate Low analyte recovery rate.2 Leakage 6.1 Leakage 1. pre-heat the rack and vacuum cover (30 min) 2. use genuine BUCHI glassware 3. clean interface between rack and platform 4. control heat transfer medium level 5. use appendix sleeves 6. check system for leakages 1. use genuine BUCHI glassware 2. check system for leakages 3. make sure the cooling loop is closed and the chiller is working properly 4. use a cooled receiving vessel or cool the receiving vessel in an ice bath 5. use a post-pump secondary condenser 1. check system for leakages 2. make sure appendix is chilled properly 3. use Flushback module 4. keep analytes dispersed in solution by speeding up rotation 5. shorten pressure gradient program 6. reduce rack temperature 4.3, A prerequisite for an efficient concentration is a tight system. In order to determine the leak rate, i.e., the pressure increase of a supposedly tight system per time, close the vacuum line between the Woulff bottle and the vacuum pump with a clamp. This measure ensures that the leak rate of the vacuum pump does not contribute to the leakage of the Syncore system. A slightly leaky pump will just need to work more to achieve the set pressure. On the contrary, a leaky Syncore system will lead to loss of solvents and analytes. The tightness of the Syncore system is tested in a closed, empty and completely dry system by stopping evacuation when the set vacuum of 50 mbar is reached. Then, the vacuum is monitored over a period of 2 minutes. In case the system is not completely dry (vessels, vacuum cover, tubing, condenser, receiving vessel), an equilibrium of the vapor and liquid phase in the system will always settle which will influence the pressure increase per time, i.e., the leak rate.

31 SECTION I Syncore SYSTEM 31 Table 6.2. Expected typical values for the tightness test of a dry Syncore system Syncore system set vacuum pressure increase 50 mbar 5 mbar/min Pump end vacuum < 15 mbar For the Analyst configurations, the overall leak rate must not exceed 15 mbar/min. Typically, the observed leak rates are lower, as listed in Table 6.2. If the results of the test do not comply with these values, the Syncore system has to be checked systematically for leaks to exclude any possible source. For this purpose, follow the order showed in Table 6.3. Table 6.3. Systematic tightness check for the Syncore system Module Issue / preparation Remedy Pump Primary condenser Vacuum cover Complete system connections at Woulff bottle insert an extra vacuum tubing between Woulff bottle and vacuum pump[12] vacuum connections close GL14 sealing cap put a rubber plug in each position inhomogeneous sample vessel height sample vessel border defective sealing discs damaged clamp newly inserted vacuum line between Woulff bottle and vacuum pump clamp vacuum line between Woulff bottle and primary condenser check leak rate check connection sealing caps for damages check sealing and sealing caps for damages check leak rate and replace caps if needed check and replace O-rings if needed replace brittle vacuum tubing use BUCHI sample vessels replace sample vessel replace sealing discs If the system is checked to be tight, but the set pressure can still not be achieved, the problem could be a contaminated pump. When the solvents cannot be condensed at the primary condenser, they will pass through the pump and possibly condense there lowering the pumping power. In this case, the pump needs to be cleaned. For cleaning the pump, all connections to the pump and the silencer have to be removed. The pump is switched on and a small amount of acetone is injected to the inlet side of the pump. The solvent coming out at the pump outlet should be adsorbed with a paper towel or similar to avoid any splashes. Wait until the pump makes a normal sound and repeat if necessary.[13]

32 32 SECTION I Syncore SYSTEM 6.2 Inhomogeneous concentration If inhomogeneous concentration is observed, make sure that concentration does not start before a heat-up time of 30 minutes. In case non-buchi glassware with inadequate specifications are used, it is possible that external air enters the sample vessels because of poor sealing and, through turbulence in the vapor phase, the position is evaporated faster. The high quality of BUCHI Syncore sample vessels guarantees very specific tolerances. In addition, the Syncore platform and the rack should be checked visually for scratches, chemical contamination, dust or mechanical damage. A smooth and even surface is a prerequisite for efficient and uniform heat transfer. Make sure that the rack fits perfectly on the platform, press until it snaps into place and no gap is visible between the platform and the rack. Fix the rack by the screws in the corners. If needed, fill the air gap between the platform and the rack with a thin film of propylene glycol, or glycerine.[8] Furthermore, check the level of the heat transfer medium between rack cavity and sample vessel. When using sample vessels with appendices smaller than 3 ml, it is important to use the appendix sleeves to isolate the chilled zone from the heated zone. If the appendix sleeves are missing or wrongly placed, the heat transfer medium mixes with the chilled zone medium due to the orbital movement and the evaporation rate will be reduced. Finally, perform a tightness check to make sure that there are no leaks (Table 6.3). 6.3 Insufficient solvent recovery rate Evaporated solvent that is not recovered in the receiving vessel escapes into the environment. Since evaporated solvents may be harmful to people working in the proximity of the device and the environment, solvent loss must be prevented. Unwanted release of solvent vapor is avoided by sealing possible leaks (using BUCHI sample vessels and following the procedure showed in chapter 6.2) and optimizing the load of the condenser (chapter 4.5) by adapting pressure and/or temperature of the system as well as by installing a cooled receiving vessel and a post-pump secondary condenser. The cooling lines that chill the different modules should be connected in series starting at the primary condenser. The correct functioning and flow of the cooling medium can be observed with the help of a flow indicator (Figure 2.14). After placing the samples in the rack, the vacuum cover has to be closed immediately and the concentration process can be started. When closing the pre-heated vacuum cover, make sure to avoid skin burns. If necessary, use protective gloves.

33 SECTION I Syncore SYSTEM Re-condensation in sample vessels with appendix After the concentration process has finished, it is important to stop the procedure to avoid the pre-defined residual volume to evaporate excessively. The chilled zone keeps the residual volume in the appendix at a constant volume for an extended period of time, but losing highly volatile compounds is still a risk if the vacuum is too prolonged and aggressive. An abrupt release of the vacuum can lead to re-condensation of the solvent in the sample vessel and in the worst case to cross-contamination. Gentle venting is recommended. As a guideline, the vacuum should be released by programming a pressure gradient from the final pressure to ambient pressure taking at least 1-2 minutes (chapter 4.4.2). 6.5 Contamination and low analyte recovery rate Cross-contamination means transport of analytes from one sample to another by an evaporation-condensation process or after bumping. Cross-contamination is most likely for highly volatile compounds that can move from one sample vessel to the next. Here, we refer to a best@buchi publication showing that with the Syncore, parallel concentration can be performed without cross-contamination (e.g., naphthalene amounts of less than 0.1 % were found in the blank samples).[8] In addition, it is important to avoid condensation of the analytes in the vacuum cover that might drop into another sample vessel by the rotation of the vacuum cover. The vacuum cover should thus be heated to at least 5 C higher than the expected vapor temperature. After each concentration run, the glassware has to be thoroughly cleaned. This guarantees good recoveries and measuring precision without carry-over from earlier experiments. Because some analytes tend to adsorb onto glass surfaces contaminated with organic impurities, the cleaning effect is considerably improved by employing alkaline cleaners. For environmental analyses, it is moreover recommended to deactivate the glassware in the oven at 450 C.[8] In case the concentration performed is always the same and the analytic results show good recoveries, it is not necessary to remove the glass plate of the vacuum cover after every run. It is sufficient to rinse the vacuum cover through the sample holes and/or the vacuum connection with a wash bottle containing alcohol. To clean the glass plate of the vacuum cover, it has to be removed by releasing the two clamping screws. Use a sponge dampened in alcohol to clean the coated plate of the vacuum cover. The EMATAL coating of the vacuum cover must never be damaged or scratched with hard brushes or other hard parts. After cleaning, it is essential to thoroughly dry the vacuum cover and its heating system to prevent any short circuit. The use of pressurized air for this purpose is recommended. The sealing discs can be cleaned with a mild detergent in water or in alcohol. If they are severely contaminated, we recommend replacing the sealing discs with new ones. A special Syncore tool is included with the system to remove the sealing discs without damaging them. In general, we recommend to clean the vacuum cover at least once a day with a wash bottle. To guarantee a longer lifetime of the vacuum cover and better results, it is advisable to clean it by removing the glass plate and the sealing discs in regular time intervals.