Subhrakanti Saha

Solid probe assisted nanoelectrospray ionization mass spectrometry for biological tissue diagnostics

To perform remote and direct sampling for mass spectrometry, solid probe assisted nanoelectrospray ionization (SPA-nanoESI) has been newly developed. After capturing the sample on the tip of the needle by sticking it to the biological tissue, the needle was inserted into the solvent-preloaded nanoESI capillary from the backside. NanoESI gave abundant ion signals for human kidney tissues and the liver of a living mouse. The method is easy to operate and versatile because any biological specimen could be sampled away from the mass spectrometer. Minimal invasiveness is another merit of this method.

Direct detection of trace level illicit drugs in human body fluids by probe electrospray ionization mass spectrometry (PESI-MS)

Detection of illicit drugs by ambient mass spectrometry has been gaining attention due to the unique advantage of detecting trace levels of chemicals from complex matrices without or with minimal sample pretreatment. This paper reports the application, characteristics and advantages of probe electrospray ionization mass spectrometry (PESI-MS) for rapid, sensitive and direct detection of methamphetamine, morphine, cocaine and codeine from human urine, oral fluid and plasma. The limits of detection (LODs) of various illicit drug standards were found to be 2–5 ppb and the trace levels of drugs were confirmed by their exact masses obtained using an ‘Exactive Orbitrap’ mass spectrometer. Here, for the first time, we evaluate the quantitative capabilities of PESI-MS from urine, oral fluid and plasma using methamphetamine as a representative illicit drug and N-benzylmethylamine as an internal standard. The LODs for illicit drugs in body fluids were one to two orders of magnitude higher compared to the standard samples and the relative standard deviations for the quantitative analysis were found to be less than 20%. As PESI is a solid needle based ambient electrospray system and free from clogging problems, it can easily be used as a spraying and direct ionization source for complex liquid mixtures.

Direct analysis of anabolic steroids in urine using Leidenfrost phenomenon assisted thermal desorption-dielectric barrier discharge ionization mass spectrometry.

Rapid detection of trace level anabolic steroids in urine is highly desirable to monitor the consumption of performance enhancing anabolic steroids by athletes. The present article describes a novel strategy for identifying the trace anabolic steroids in urine using Leidenfrost phenomenon assisted thermal desorption (LPTD) coupled to dielectric barrier discharge (DBD) ionization mass spectrometry. Using this method the steroid molecules are enriched within a liquid droplet during the thermal desorption process and desorbed all-together at the last moment of droplet evaporation in a short time domain. The desorbed molecules were ionized using a dielectric barrier discharge ion-source in front of the mass spectrometer inlet at open atmosphere. This process facilitates the sensitivity enhancement with several orders of magnitude compared to the thermal desorption at a lower temperature. The limits of detection (LODs) of various steroid molecules were found to be in the range of 0.05-0.1 ng mL(-1) for standard solutions and around two orders of magnitude higher for synthetic urine samples. The detection limits of urinary anabolic steroids could be lowered by using a simple and rapid dichloromethane extraction technique. The analytical figures of merit of this technique were evaluated at open atmosphere using suitable internal standards. The technique is simple and rapid for high sensitivity and high throughput screening of anabolic steroids in urine.

Development of Sheath-Flow Probe Electrospray Ionization Mass Spectrometry and Its Application to Real Time Pesticide Analysis

For the real time and direct analysis of chemical constituents from living beings and dry sample, sheath-flow probe electrospray ionization mass spectrometry (SF-PESI-MS) has been newly developed. The components from dry or semidry biological tissues can be extracted using the solvent and picked up by the needle for electrospray. This technique was applied to real-time pesticide analysis of living plants. The results have been validated with that of a well-known system, liquid extraction surface analysis mass spectrometry (LESA-MS). It is demonstrated that SF-PESI-MS can produce reasonable ionization efficiency, which is confirmed by LESA-MS.

Biomolecular analysis and biological tissue diagnostics by electrospray ionization with a metal wire inserted gel-loading tip.

A metal wire-inserted disposable gel-loading tip was examined as an electrospray emitter. Its performance was similar to that of conventional electrospray ionization (ESI) with a relatively low flow rate (~100 nL/min) and without the need for solvent pumps. It was also used as an emitter for solid probe-assisted ESI (SPA-ESI) (e.g., biofluid was sampled from the biological tissue by a needle and was inserted into the solvent-preloaded gel-loading tip). Selective detection of lipids and proteins, such α and β chains of hemoglobin could be accomplished by choosing appropriate solvents. A suitable protocol for cancer diagnosis was established by this method. A good figure of merit of this method is its applicability to biological tissue diagnostics with high cost efficiency and on a disposable basis.

Probe electrospray ionization (PESI) mass spectrometry with discontinuous atmospheric pressure interface (DAPI).

Probe electrospray ionization (PESI) using a 0.2 mm outside diameter titanium wire was performed and the generated ions were introduced into the mass spectrometer via a discontinuous atmospheric pressure interface using a pinch valve. Time-lapse PESI mass spectra were acquired by gradually increasing delay time for the pinch valve opening with respect to the start of each electrospray event when a high voltage was applied. The opening time of the pinch valve was 20 ms. Time-resolved PESI mass spectra showed marked differences for 10 mM NaCl, 10−5 M gramicidin S and insulin in H2O/CH3OH/CH3COOH (65/35/1) with and without the addition of 10 mM CH3COONH4. This was ascribed to the pH change of the liquid attached to the needle caused by electrochemical reactions taking place at the interface between the metal probe and the solution. NaCl cluster ions appeared only after the depletion of analytes. For the mixed solution of 10−5 M cytochrome c, insulin, and gramicidin S in H2O/CH3OH/CH3COOH (65/35/1), a sequential appearance of analyte ions in the order of cytochrome c → insulin → gramicidin S was observed. The present technique was applied to three narcotic samples, methamphetamine, morphine, and codeine. Limits of detection for these compounds were 10 ppb in H2O/CH3OH (1/1) for the single sampling with a pinch valve opening time of 200 ms.

Desorption in Mass Spectrometry

In mass spectrometry, analytes must be released in the gas phase. There are two representative methods for the gasification of the condensed samples, i.e., ablation and desorption. While ablation is based on the explosion induced by the energy accumulated in the condensed matrix, desorption is a single molecular process taking place on the surface. In this paper, desorption methods for mass spectrometry developed in our laboratory: flash heating/rapid cooling, Leidenfrost phenomenon-assisted thermal desorption (LPTD), solid/solid friction, liquid/solid friction, electrospray droplet impact (EDI) ionization/desorption, and probe electrospray ionization (PESI), will be described. All the methods are concerned with the surface and interface phenomena. The concept of how to desorb less-volatility compounds from the surface will be discussed.

Untreated and dried sample analysis by solid probe assisted nanoelectrospray ionization mass spectrometry

The present paper describes the application of solid probe assisted nanoelectrospray ionization mass spectrometry (SPA-nanoESI-MS) for the direct analysis of samples in solid or dried form. The experimental procedure is simple and requires a metallic needle to touch the sample surface followed by inserting the needle into a solvent preloaded nano-capillary. A number of real-world samples in solid or dried form comprising proteins, drugs in tablets, illicit drugs in dried urine, and lipids in tissues were analyzed to evaluate the applicability of the technique in diverse fields. This technique can produce high quality mass spectra without clogging the capillary tip. The quantitative aspect of this technique was evaluated using morphine from dried urine. In addition, biofluids/biomolecules captured on the needle tip and stored for several days at room temperature produced almost similar spectra to those obtained for fresh samples of cancerous and noncancerous tissues. The high sensitivity, versatile applicability and capability of dried sample analysis extend the scope of SPA-nanoESI to new ventures like bioanalytical and forensic analysis as well as clinical diagnosis.