Significant Reduction in Acetonitrile Vapors with the VapLock Closed Solvent Waste System: Ensuring Health and Safety in HPLC Laboratories
The amount of acetonitrile found in the laboratory air was cut in half around the HPLC system on which the VapLock system was installed. In laboratories with multiple HPLC or LCMS systems, the reduction of indoor air pollution could be dramatically reduced ensuring the health and safety of laboratory employees.
Solvents are an important part of many laboratory processes and analyses. They are ubiquitous in the laboratory and, while they are necessary for many procedures, solvents can also be a significant source of contamination. Most solvents are compounds that readily dissolve other compounds and tend to be volatile in nature with boiling points in the range of less than 200 ºC. Compounds with boiling points less that 100 ºC are often referred to in some fields (such as by the World Health Organization) as VVOC (very volatile organic compounds), while compounds with boiling points in the range of 50 ºC to about 260 ºC are most commonly designated as VOC (volatile organic compounds) (Table 1).
Table 1. Volatile Organic Compound Designations (adapted from WHO & EPA)
| Description | Abbreviation | Approximate Boiling Point Range |
| Very Volatile Organic Compounds | VVOC | < 100 ℃ |
| Volatile Organic Compounds | VOC | 50 ℃ – 260 ℃ |
One of the most important factors in a solvent becoming an airborne pollutant is the material’s evaporation rate. Evaporation rate reflects several factors including the temperature of the environment, the vapor pressure of the liquid at that temperature, the thickness or depth of the liquid, the velocity of the air in the space, and the latent heat of vaporization from the material under the surface of the liquid.
Vapor pressure is the pressure produced by a vapor above a solid or liquid when it is in equilibrium at a set temperature in a closed system. Vapor pressure describes the probability of particles to liberate from the solid or liquid phase into the vapor. Materials with high vapor pressures at normal temperatures are called volatile.
If factors such as air velocity or temperature increase, the rates also increase. As temperatures increase, the energy of the molecules increase and allows more partitioning of molecules in the liquid or solid into the vapor phase. Most standard vapor phases are calculated at a standard temperature of T=25 ºC. Vapor pressures at other temperatures need to incorporate additional constants into the calculation.
Evaporation rates are important in laboratory safety. Solvents with high evaporation rates, such as acetone and methylene chloride, dissipate into the laboratory air faster than non-volatile solvents such as water. Evaporation rates are inversely proportional to boiling point, the lower the boiling point, the higher the evaporation rate. Many evaporation rates are standardized against a reference compound, such as ether or n-butyl acetate (BuAc). Slowly evaporating solvents have evaporation solvents under 0.8, compared to BuAc; fast evaporating compounds have rates over three compared to BuAc (Table 2).
Table 2. Common Laboratory Solvent Evaporation & Vapor Pressure Data
| Solvent | Approximate Evaporation Rate (BuAc = 1) | Boiling Point (F) | Vapor Pressure (mmHg) |
| Methylene Chloride | 15 to 30 | 104 | 350 |
| Acetone | 10 to 15 | 133 | 180 |
| Methanol | 2 to 4 | 147 | 96 |
| Ethyl Acetate | 4 to 5 | 171 | 73 |
| Ethanol | 2 to 3 | 173 | 33 |
| Acetonitrile | 6 | 179 | 89 |
| Isopropanol | 2 | 181 | 33 |
| Water | <0.5 | 212 | 24 |
| Toluene | ~ 2 | 232 | 21 |
Solvents are an integral component of liquid chromatography systems being at the center of a liquid mobile phase. Normal phase liquid chromatography (NPLC), or adsorption chromatography, is where the mobile phase consists of a nonpolar solvent like hexane, while the stationary phase is composed of polar materials such as silica. The most commonly used mode of liquid chromatography is reversed phase liquid chromatography (RPLC), or partition chromatography, in which the mobile phase is polar (commonly acetonitrile, methanol and water) while the stationary phase is composed of nonpolar materials.
Mobile phase is stored in reservoir bottles, usually atop or near the rest of the HPLC system. Many reservoir systems, including caps, contain a variety of inlets or holes to allow for the passage of tubing and aeration. Often several of these holes or inlets are left open due to either unuse or to allow venting of pressure in the bottle. However, the venting of solvents like acetonitrile and methanol can contribute to the overall laboratory air pollution.
In a Spex study, the amount of contaminants were measured in our laboratory air at two points in time; before and after the installation of a VapLock Closed Solvent Waste System to control solvent evaporation. Air sampling SUMMA canisters were obtained from SGS laboratories.
Five locations were targeted for air monitoring including:
- SVOA QC Laboratory Benchtop – On top of the sample preparation bench in the SVOA QC laboratory within ten feet of two LCMS systems and one HPLC system all equipped with reservoir bottles containing acetonitrile, water and methanol
- SVOA LC Waste Container – Next to the HPLC system waste container under the laboratory bench
- SVOA LC Reservoir Top – Atop the HPLC system along side the mobile phase bottles
- VOA QC Desk – On top of the desk in VOA QC laboratory which contains only GCMS instruments
- Outdoor Control – Outside Spex facility on the property to create an environmental blank control
All canisters were prepared by SGS and placed by Spex personnel.
The first set of canisters were tested prior to installation of the VapLock system (Summer 2021). The reservoirs of the HPLC system had multiple open vents.
The laboratory HPLC system was then equipped with a VapLock system, complete with a . The mobile phase reservoirs were equipped with the VapLock system using the fitted caps (Figures 1 & 2) and the VapLock instructions.
Figure 1. Installation Instructions for HPLC Reservoirs VapLock System
Tube and Cap Installation
 |  |  |
| Secure cap to the solvent reservoir by rotating clockwise until hand-tight. Do not overtighten, as you may crack the threaded collar of the cap assembly. | Orient fitting so threads are pointed towards the VapLock Solvent Delivery Cap, then insert tubing into fitting. | Orient ferrule so the taper points towards the bottom of the fitting. Then install assembly into available threaded port. |
 |  |  |
| When using an optional inline filter, cap must be removed then reinstalled. | Before tightening fitting, adjust length of tube(s) to desired depth within reservoir. | Secure fitting to the port by tightening until finger tight, then turn fitting an additional 1/4 turn. Do not overtighten as it may cause fitting to cross-thread. |
Figure 2. Installation Instructions for VapLock Air Inlet
Installation of Stand-Alone Air Inlet Valves
 |  |  |
| Insert stand-alone inlet valve into an open port in solvent cap by tightening until finger tight – do not overtighten. | Check to make sure all tubing and fittings in other ports are secure. | If there are any open ports in the solvent cap, make sure these are plugged appropriately. |
The waste container was then fitted with the appropriate VapLock cap and indicator (Figure 3).
Figure 3. VapLock Waster Container Fittings
The laboratory air was resampled more than two months after installation of a VapLock Closed Solvent Waste System (late Fall 2021).
Containers were allowed to passively sample the laboratory air for twenty-four hours before being closed and sent back to SGS for testing using the TO-15 method with the addition of the measurement for acetonitrile.
Results and Conclusions
The testing laboratory was unable to provide measurements for methanol in the air samples. Fortunately, the most commonly used mobile phase in our laboratory HPLC systems is acetonitrile which was able to be measured.
The control outdoor container measured minimal amounts of acetonitrile in the range of less than 10 ppbv both before and after the installation of the VapLock system. Inside the laboratory, in each of the interior locations there appeared to have some level of acetonitrile vapor reduction; with the exception of the laboratory preparation bench where samples are prepared for analyses. The SVOA QC Benchtop is the site of sample processing and staging for QC analysis and often has vessels containing solvent that are dispensed, opened or aliquoted from one container (i.e. ampule to sample vial, bottle to reservoir, or flask to vial) to another. The vapors in this site can vary greatly with laboratory procedures being performed. While the VapLock system with the closed solvent waste system can reduce vapors at vessels at the HPLC system; laboratory contamination can still occur when solvents are opened in uncontrolled or unvented areas of the laboratory. *
The locations associated with direct acetonitrile concentrations (i.e., top of the HPLC and waste container) both showed significant reduction of acetonitrile vapors of approximately 50% to 70% (Table 3).
Table 3. Acetonitrile Reduction in Laboratory Sampling Locations
| Location | Pre-Installation (ppbv) | Post Installation (ppbv) | % Change |
| Outdoor Control | 9.4 | 3.6 | N/A |
| VOA QC Desk | 1610 | 674 | –58% |
| SVOA QC Benchtop | 2250 | 2450 | 9% |
| * SVOA HPLC Top Reservoirs | 3470 | 1840 | –47% |
| SVOA HPLC Waste Container | 3770 | 1170 | –69% |
The amount of acetonitrile found in the laboratory air was cut in half around the HPLC system on which the VapLock system was installed. In laboratories with multiple HPLC or LCMS systems, the reduction of indoor air pollution could be dramatically reduced ensuring the health and safety of laboratory employees.
Outcome
The amount of acetonitrile found in the laboratory air was cut in half around the HPLC system on which the VapLock Closed Solvent Waste System was installed. In laboratories with multiple HPLC or LCMS systems, the reduction of indoor air pollution could be dramatically reduced ensuring the health and safety of laboratory employees.
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