Faster Sample Filtration for HPLC with a Vacuum-driven Multi-sample Device

Janet L Smith,
Biochemical Scientist, MilliporeSigma

Introduction

Sample prefiltration is an important process that removes contaminants from samples for High Performance Liquid Chromatography (HPLC) prior to analysis. Filtering out contaminants can help prolong column life and can contribute to data reproducibility by removing interfering impurities from the sample matrix. Samples for HPLC / UHPLC analysis must be particle-free and completely soluble in the solvent compatible with the chromatography system, and sample filtration serves to alleviate concerns regarding the contribution of particulates to unexpected peaks in HPLC traces. While syringe filtration is effective and accessible, employing this method to filter more than a few samples per day can quickly become inefficient and time-consuming.  The Samplicity® G2 filtration system was developed as a better way to use Millex® syringe filters by eliminating the excessive hands-on time associated with preparing multiple samples while offering a simplified, ergonomic workflow. The Samplicity® system combines simple adapter funnels and standard Millex® 33 mm syringe filters with vacuum-based filtration to enable processing of up to 8 samples directly into standard HPLC vials. This method enables faster sample filtration when compared with the pressure-driven syringe technique, and eliminates the manual fatigue that can result from filtering multiple samples in succession.  Here, we performed manual syringe filtration in parallel with vacuum-driven filtration with the Samplicity® G2 system, filtering samples relevant to pharmaceutical and food/beverage processing applications. Results are used to compare filtrate yields obtained as well as the time needed to filter samples simultaneously with multi-sample vacuum filtration versus identical samples filtered sequentially by manual pressure, using an array of membrane types and pore size formats.

Materials and Methods

The viscosity of solutions filtered was measured on a Brookfield Model LVDV-II Viscometer fitted with spindle S61 at 60 rpm for low viscosity measurements.  Viscosities were calculated as the average of triplicate measurements.  Sample filtration and membrane selection For all experiments, samples were filtered through non-sterile Millex® syringe filters with Durapore® PVDF (polyvinylidene fluoride), nylon, or Millipore Express® PLUS PES (polyethersulfone) membranes. Filtration was performed either with a 10 mL syringe fitted to the Millex® filter, or with funnels inserted into Millex® filters using the Samplicity® G2 filtration system. Where the Samplicity® G2 system was used, the following procedure was employed. The system was connected to a vacuum source, and after placement of HPLC vials in the vial tray, the transparent tray lid was closed. Sample hatches in the lid were opened only where samples were present in order to place filters over the openings, after which funnels were placed into the filters. Sample was added to each funnel.  After ensuring that ports not occupied by sample were closed, vacuum was applied using the lever on the left side of the Samplicity® G2 base. Following filtration, vacuum was removed, and restoration of ambient pressure was verified prior to removal of the filters and transparent cover. See Figure 1 for procedure.

Comparison of Filtration Time

Filtration studies were conducted by filtering 2 mL of each sample either by manual syringe filtration or by adding 2 mL of each sample to the funnel as described in the Samplicity® G2 workflow process and filtration steps (Figure 1). Average filtration time was reported as the average of 8 samples for each condition.

Sequential vs. Batch Filtration Processing

Samplicity® G2 Process Steps
Insert 8 HPLC vials into base and place lid over vial tray
Insert 8 Millex® filters into lid
Insert 8 funnels into Millex® filters
Pipette 8 2-mL samples into funnels
Turn vacuum on
Discard funnels and filters
Disassemble and remove vials



Syringe Filtration Steps
Unwrap syringe REPEAT THESE 4
STEPS 8 TIMES
Pull sample into syringe
Attach Millex® filter to syringe
Push plunger to filter the sample

Figure 1. Streamlined, batch processing of eight samples using the Samplicity® G2 vacuum filtration system provides ergonomic benefits and significant time savings over sequential syringe filtration.

The Samplicity® G2 system filters 8 samples faster than manual syringe method for all sample types

Using the steps indicated in Figure 1, sample processing time was compared between the Samplicity® G2 filtration system and manual syringe filtration, processing eight samples at a time, using a variety of membrane types in 33 mm Millex® devices and various test solutions. The Samplicity® G2 filtration system provided between 28% and 62% time savings, depending upon sample characteristics, membrane material, and pore size.

Samplicity® G2 filtration reduces sample processing time for all membrane types and sample viscosities

In order to assess the effect of membrane composition, pore size, and sample viscosity on filtration efficiency, we filtered eight samples each of the water, acetaminophen dissolution, and ketchup dilution samples described previously using Millex® devices manufactured with membranes composed of Durapore® PVDF, nylon, or Millipore® Express PLUS PES. Samples were filtered using two pore sizes (0.45 µm, and 0.22 or 0.2 µm) for each membrane material. In all cases, the time required to filter eight 2-mL sample volumes was remarkably reduced using the Samplicity® G2 protocol (Figure 2). By comparing the mean weight  of the filtrate obtained from each of the eight sample groups, we concurrently discovered that final filtrate volume from the Samplicity® G2 samples was 14-25% greater than that obtained by manual syringe filtration of identical samples (data not shown). These results demonstrate the compatibility and enhanced efficiency of the Samplicity® G2 system with diverse Millex® devices and sample types.

 

  Samplicity® G2 Filtration System time benefit over manual syringe (per 8 samples) Samplicity® G2 Filtration System processing time (minutes; 8 samples)   (10 mL) Syringe processing time (minutes; 8 samples)
Sample Type Min. Max. Min. Max. Min. Max.
Milli-Q® Water 54% 62% 1.88 2.08 4.08 5.22
Dissolution Testing 40% 49% 2.23 2.68 3.85 5.17
5% Ketchup 28% 60% 3.10 4.15 4.93 9.23

Table 1. Samplicity® G2 Filtration System enables faster processing and filtration than manual syringe filtration when 8 samples are processed at one time

(A) Processing and Filtration Time for 2 mL Milli-Q® Water Samples (viscosity 2.4 cps) N=1 set of eight, 33 mm Millex® Syringe Filters

(B) Processing Processing and Filtration Time for 2 mL 600 mg Acetaminophen in Simulated Gastric Fluid Dissolution (viscosity 2.0 cps) N=1 set of eight, 33 mm Millex® Syringe Filters

(C) Processing and Filtration Time for 2 mL 5% Ketchup (viscosity 4.6 cps) N=1 set of eight, 33 mm Millex® Syringe Filters

Figure 2. Time needed to filter samples with the Samplicity® G2 filtration system vs by manual syringe. Equivalent sets of eight 2 mL samples of Milli-Q® filtered water (A), a dissolution of 650 mg acetaminophen in simulated gastric fluid (B) or a 5% ketchup solution (C) were prepared and filtered as described. Sample sets were filtered via Durapore® PVDF (0.22 or 0.45 µm pore size), nylon (0.2 or 0.45 µm), or Millipore Express® PLUS PES (0.22 or 0.45 µm) 33 mm Millex® devices. Syringe processing times are the average of eight individual devices.

Conclusions

Filtration of chromatography samples reduces contamination peaks in chromatography data, and protects HPLC columns by removing particulate contaminants that can cause column damage. As the number of samples increases, manual pressure filtration by syringe can become a time-consuming process that increases the risk for repetitive-stress injury. For HPLC sample preparation, the Samplicity® G2 filtration system provides an alternative to manual syringe filtration. The data above demonstrate time savings of at least 28% when preparing eight samples at one time, with the exact processing time dependent upon sample and membrane type. For labs employing HPLC and UHPLC and processing multiple samples per run, the Samplicity® G2 filtration system provides the opportunity to markedly increase efficiency through time savings without compromising final filtrate yield.

Materials

     
Product# Description
SAMP2LCRK Millex-LCR for Samplicity G2, 0.45 µm, hydrophilic PTFE, 33 mm, non-sterile,
SAMP2GLNK Millex-LG for Samplicity G2, 0.20 µm, hydrophilic PTFE, 33 mm, non-sterile,
SAMP2HVNK Millex-HV 0.45 for Samplicity G2 µm, PVDF, 33 mm, non-sterile,
SAMP2GVNK Millex-GV Filter for Samplicity G2, 0.22 µm, PVDF, 33 mm, non-sterile,
SAMP2HNNK Millex-HN, 0.45 for Samplicity G2 µm, nylon, 33 mm, non-sterile,
SAMP2GNNK Millex-GN for Samplicity G2, 0.20 µm, nylon, 33 mm, non-sterile,
SAMP2HPNK Millex-HP 0.45 for Samplicity G2 µm, PES 33 mm, non-sterile,
SAMP2GPNK Millex-GP Filter for Samplicity G2, 0.22 µm, PES 33 mm, non-sterile,
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