Sample Preparation techniques are often multistep, time consuming and labor intensive that can take up to 60-80% of the total analysis time depending on the application. There is an increased focus on improving the process by shortening the time, cutting costs and reducing the number of sample preparation steps₍₁₎. The analysis of biological samples is an interdisciplinary task including therapeutic drug monitoring, pharmacokinetic studies, clinical analysis, drug metabolism and forensic analysis. Many biological fluids are not suitable for direct liquid chromatography-mass spectrometry analysis due to high sample complexity and high content of interfering compounds with target analytes often present in low concentrations₍₂₎. Therefore, sample preparation is often required for bioanalytical methods.

Pipette tips are a common laboratory consumable that any analytical scientist or technician across disciplines will know how to use. Pipette tips are often used as a means to transfer samples to facilitate conventional sample preparation techniques. Conventional sample preparation techniques like protein precipitation (PP) and solid phase extraction (SPE) are widely performed and accepted methods₍₃₎. DPX has developed patented technologies that utilize pipette tips to perform this sample preparation. This article explores the drawbacks of traditional approaches to performing SPE or PP and discusses the benefits of switching to a tip-based sample preparation method.

PP is considered to be the simplest extraction approach. However, an additional centrifugation or filtration step is required in order to separate the resultant precipitate from the analyte to provide a cleaner solution for analyses₍₃₎. Although recent products have automated the PP step, centrifugation is offline and labor intensive. INTip Filtration from DPX utilizes a patent-pending Tip-on-Tip technology designed to promote the simplification and automation of complex sample preparation. ToT Filtration combines a top wide bore conductive tip with a bottom filtration tip to facilitate automated, high throughput protein precipitation, filtration, beta-glucuronidase enzyme removal or any other particulate removal down to less than 1 µm.

INTip filtration can replace centrifugation steps, filter plates or syringe filters. Filtration tips can be ordered in low porosity, dual phase or single phase varieties and offer a low cost/ high efficiency solution. There are several published application notes utilizing this technology including:

• Automated Method LC-MS/MS Quantitation of Testosterone from Serum
• Sensitive Analysis of Therapeutic and Abused Drugs in Whole Blood Using Tip-on-tip Technology with LC-MS/MS
• Automated Protein Precipitation and Dispersive Pipette Extraction of Serum Samples for Vitamin D3 and D2 by LC-MS/MS

Schematic of Tip-on-Tip Filtration workflow for the Quantitation of Testosterone from Serum

SPE is a popular sample pre-treatment enabling purification and concentration of target analytes₍₁₎. A wide range of currently available SPE sorbents ensures various selectivity and are available in various formats including column cartridges, discs and well-plates and pipette tips, sometimes called disposable pipette tip extraction₍₃₎ (branded as Dispersive Pipette Extraction). Dispersive Pipette Extraction has been cited in numerous journal articles as a reliable option for performing solid phase extraction₍₄₎. Conventional SPE cartridges are used with a vacuum or positive-pressure manifold. These formats suffer from flow rate control issues resulting in columns drying out and/or inefficiencies like channeling and low recoveries ₍₃₎.

INTip SPE utilizes a patented device that is unique from all other SPE devices because sorbent material is loosely contained between two barriers within a pipette tip. The design allows a sample solution to aspirate into the pipette tip and mix with the sorbent. The disperser helps to perturb the sample solution and loose sorbent during multiple aspirate and dispense steps. Every sorbent particle actually faces analyte several times. Mixing during aspiration and dispense steps provide enhanced interaction between the sorbent and analyte providing optimal binding efficiencies. This is contrary to conventional SPE, where a greater amount of sorbent is needed because the analyte comes into contact with the sorbent particles only once₍₅₎. This process is not dependent on sample flow-rate₍₆₎ and the highly efficient interaction of the sorbent and sample solution results in fast extraction times, ideal analyte recoveries and minimized matrix effects.

DPX Technologies sources commercially available chemistry in a range of phases to provide  selectivity for a diverse spectrum of analytes. XTR tips are manufactured to order per custom specifications. Tips can hold 1 – 100 mg of sorbent depending on the format. Method development can be done with a 1 mL Universal style tip that fits most handheld pipettes with no additional hardware like vacuum or positive pressure manifolds required. DPX Technologies also offers a 1 mL Pneumatic Extractor which can process 24 – 96 samples at one time. This allows even small labs to increase sample throughput to save time and costs.

Switching from manual to automated workflows is as easy as switching the DPX tip format. INTip SPE is available in a variety of tip formats that are compatible with a wide range of automated pipetting platforms. Methods that started out manually can be seamlessly integrated into an automated workflow. DPX offers automation support and has many pre-scripted applications available for platforms like Hamilton Robotics, Integra or the epMotion from Eppendorf. DPX also works with Gerstel and methods for their MPS system can be found on their website.

1. Nováková, LCGC,  29, 9 (2016)
2. L. Nováková, J. Chromatogr. A 1292, 25 (2013).
3. L. Nováková and H. Vicková, Anal. Chim. Acta 656, 8 (2009).
4. DPX Technologies, Rebrand Press Release
5. P. L. Kole, G. Venkatesh, J. Kotecha, and R. Sheshala, Biomed. Chromatogr. 25, 199 (2011).
6.  Chaves, A. R. J. Chromatography A 1399, 1 (2015)