Replaceable electrospray emitter system for liquid separation and electrospray ionization

Abstract

An integrated system for liquid separation and electrospray ionization, comprising a replaceable emitter and a column portion. The replaceable emitter includes an emitter capillary; a conductive sheath; a conductive nut electrically coupled to the conductive sheath; and a plug-type fitting. The column portion includes a capillary column; a plastic molding encasing the capillary column; a receiving fitting for receiving the plug-type fitting and threadingly engage with the conductive nut; and a conductive stop.

Description

REPLACEABLE ELECTROSPRAY EMITTER SYSTEM FOR LIQUID SEPARATION AND ELECTROSPRAY IONIZATIONCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to US Provisional Application S / N 63 / 610,622, filed December 15, 2023, the entire contents of which is incorporated herein by reference.FIELD

[0002] The present disclosure generally relates to the field of liquid chromatography including a replaceable electrospray emitter system for liquid separation and electro spray ionization.INTRODUCTION

[0003] Proteomics, being the study of protein structure and function, is a research focus for decades to come as it can allow one to elucidate the fundamentals of life and the molecular basis of health and disease. Analysis of complex protein mixtures usually involves two steps: molecular separation and idcntification / charactcrization. In the context of bottom-up proteomics experiments, proteins are subject to proteolytic digestion to break down into fragments of peptides which are then separated, usually with liquid chromatography (LC), before being introduced into an ion source of a mass spectrometer. Typically, the ion source for proteomics experiments implements electrospray ionization (ESI) to ionize the peptide to form ions that can be transported among components of a mass spectrometer.

[0004] While conventional HPLC columns (i.e. columns with fittings for connecting to conventional instruments) for use with nano-liter flow rates (also referred to as nano-LC) show superior performance, incorrect assembly of fittings and fluid connections often compromises the advantages associated with conventional nano-LC columns. In other words, incorrect connections of LC transfer tubing to the LC columns may result in leaks and consequently poor sensitivity and chromatographic separation. Also, incorrect connection of a conventional nano-electrospray emitter after the LCcolumn may give rise to undesired dead-volumes which also leads to reduced sensitivity and poor separating power.

[0005] The columns and transfer lines ordinarily used in liquid chromatography systems that employ flow rates less than 10 pL / minute most frequently have very narrow inner diameters as well as outer diameters. Consequently, such transfer lines and columns may be physically fragile. Thus, it is highly desirable to provide some means of mechanical relief from strain, pressure, bends, twists etc. such that the thin tubing components are protected and become robust enough to withstand use in everyday laboratory work.

[0006] The commonly used interface between chromatography and mass spectrometry is made up by the electrospray ion-source. In the ion source, the eluate from the LC column is passed through an emitter (also termed a needle) that is held at an electric potential that usually differs by one or more kilovolts from an opposing inlet orifice of the mass spectrometer. This enables the eluate, and subsequently the analytes, to adopt electric charges (i.e. become ionized) such that the ionized analytes may be analyzed in the mass spectrometer. The physical characteristics of a LC column and an ESI emitter affect analytical performance. For example, stationary phase chemistry, stationary phase particle size, diameter, length, and post-column dead volume of the LC column influence separation efficiency of chromatography. For ESI performance using non-conductive emitters, solution resistances cause a voltage drop that reduces the magnitude of the voltage applied to the tip of the emitter, affecting the formation of ions.

[0007] The high electric potential differences present a safety hazard if the charged areas can be touched by the operator. Thus, it is highly desirable to efficiently shield as many components as possible that are at the elevated potential. The electrospray emitter is a thin fragile component that is potentially easy to damage if not handled carefully and moreover is sharp such that injury can be caused by it. It is therefore desirable to reduce the risk of damage to the electrospray emitter and / or injury by exposure to it.SUMMARY

[0008] An integrated system for liquid separation and clcctrospray ionization can include a replaceable emitter and a column portion. The replaceable emitter can include an emitter capillary; a conductive sheath; a conductive nut electrically coupled to the conductive sheath; and a plug-type fitting. The column portion can include a capillary column; a plastic molding encasing the capillary column; a receiving fitting for receiving the plug-type fitting and threadingly engage with the conductive nut; and a conductive stop.DRAWINGS

[0009] For a more complete understanding of the principles disclosed herein, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0010] Figures 1A and IB are external views of a replaceable emitter system for electrospray ionization, in accordance with various embodiments.

[0011] Figures 2A and 2B are cross section views of the replaceable emitter system of Figures 1A and IB respectively, in accordance with various embodiments.

[0012] It is to be understood that the figures arc not necessarily drawn to scale, nor are the objects in the figures necessarily drawn to scale in relationship to one another. The figures are depictions that are intended to bring clarity and understanding to various embodiments of apparatuses, systems, and methods disclosed herein. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Moreover, it should be appreciated that the drawings are not intended to limit the scope of the present teachings in any way.DESCRIPTION OF VARIOUS EMBODIMENTS

[0013] Embodiments of a replaceable electrospray emitter system for liquid separation and electrospray ionization are described herein.

[0014] The section headings used herein are for organizational purposes only and are not to be construed as limiting the described subject matter in any way.

[0015] In this detailed description of the various embodiments, for purposes of explanation, numerous specific details arc set forth to provide a thorough understanding of the embodiments disclosed. One skilled in the ait will appreciate, however, that these various embodiments may be practiced with or without these specific details. In other instances, structures and devices are shown in block diagram form. Furthermore, one skilled in the ait can readily appreciate that the specific sequences in which methods are presented and performed are illustrative and it is contemplated that the sequences can be varied and still remain within the spirit and scope of the various embodiments disclosed herein.

[0016] All literature and similar materials cited in this application, including but not limited to, patents, patent applications, articles, books, treatises, and internet web pages are expressly incorporated by reference in their entirety for any purpose. Unless described otherwise, all technical and scientific terms used herein have a meaning as is commonly understood by one of ordinary skill in the ail to which the various embodiments described herein belongs.

[0017] It will be appreciated that there is an implied “about” prior to the temperatures, concentrations, times, pressures, flow rates, cross-sectional areas, etc. discussed in the present teachings, such that slight and insubstantial deviations are within the scope of the present teachings. In this application, the use of the singular includes the plural unless specifically stated otherwise. Also, the use of “comprise”, “comprises”, “comprising”, “contain”, “contains”, “containing”, “include”, “includes”, and “including” are not intended to be limiting. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present teachings.

[0018] As used herein, "a" or "an" also may refer to "at least one" or "one or more." Also, the use of “or” is inclusive, such that the phrase “A or B” is true when “A” is true, “B” is true, or both “A” and “B” are true. Further, unless otherwise required by context, singular- terms shall include pluralities, and plural terms shall include the singular.

[0019] A “system” sets forth a set of components, real or abstract, comprising a whole where each component interacts with or is related to at least one other component within the whole.

[0020] One challenge with integrated column-emitter systems, like EASY-SPRAY columns, is that the emitter tip does not last as long as the LC column. Users must discard the entire column if the emitter tip is damaged, dirty, or blocked even though the column is fully functional and performing as expected.

[0021] Described herein is a finger tight replaceable emitter assembly compatible with the EASY-SPRAY column design. The emitter assembly can be removed without tools or removal of the protective insulating injection molding plastic. A pug type capillary fitting is installed on the emitter inlet to ensure a proper seal and assembly of the unit. The replaceable emitter assembly can extend the life of the column by allowing customers to replace the emitter separately from the column. The emitter may become damaged during use customer improperly handling the unit or the emitter becoming blocked due to sample build up on the tip due to extended use of the unit. Allowing replacement of the emitter separately from the column can reduce waste and environmental impact.

[0022] Disclosed herein is an LC column low flow column in the EASY-SPRAY column format with a replaceable emitter tip. The emitter is held in place with a plugtype fitting, such as a NANOVIPER fitting, to ensure a near zero dead- volume connection. The EASY-SPRAY column format includes internal temperature control, safe application of electrospray voltage, and an insulating plastic encapsulating the LC column, temperature control board, and union for voltage application.

[0023] The replaceable emitter tip gives the customer the flexibility to change the emitter dimensions to better match the experimental parameters they are trying to reach. Emitter profiles along with the internal and external dimensions can be changed as long as they are assembled with a plug-type connection.

[0024] The union has a reliable liquid junction to ensure that the high voltage is applied to the liquid before entering the emitter tip inlet. The reliability of the column lifetime, union liquid junction and the ability to replace the emitter provides more versatility and long-term performance compared to the integrated column-emitter systems.

[0025] Fig. 1A shows an external view of a replaceable emitter system 10 in an attached configuration, and Fig. IB shows an external view of the replaceable emitter system 10 in a detached configuration. Fig. 2A shows a cross-section view of the replaceable emitter system 10 in the attached configuration, and Fig. 2B shows a cross section view of the replaceable emitter system 10 in the detached configuration.

[0026] Replaceable emitter system 10 includes a replaceable emitter 100 and a column portion 200. The replaceable emitter 100 includes an emitter capillary 102 with a distal end 104 formed into a tip to function as an electrospray emitter and a proximal end 106 that couples with the column portion 200. The emitter capillary 102 can include an electrically conductive capillary, such as a metal capillary or a glass capillary, e.g. glass coated with electrically conductive material. However, glass capillaries that are not conductive or coated may be used.

[0027] In various embodiments, the distal end 104 with integrated emitter tip can include a porous matrix. The porous matrix can reduce the void volume of the tip.

[0028] A protective sleeve 108 of generally cylindrical form is slidably located on the distal end 104 of the emitter capillary 102. The sleeve has a main body 110 and a base 112 of wider diameter than the main body. The protective sleeve 108 is desirably made of a rigid material, such as a metal or polymer material. In this way the rigidity of the sleeve can protect the distal end 104 of the emitter capillary 102 that it covers. Mounted about the protective sleeve 108 is an electrically conductive sheath 114, e.g. made of metal. The conductive sheath 114 has an internal diameter such as to accommodate therein the protective sleeve 108 and permit the protective sleeve 108 to slidably move in a reciprocating manner inside the sheath as further described below.

[0029] In some embodiments, the protective sleeve 108 is fixed with respect to the emitter capillary 102. However, the protective sleeve 108 is most preferably retractable, i.e. with respect to the emitter tip of the emitter capillary 102. Where the sleeve 108 is retractable, this ensures that the emitter tip is exposed when in use and thereby the sleeve 108 does not interfere, for example, with gas flows and equipotential lines around the emitter tip. Moreover, a retractable sleeve 108, when in use, does not block visibility of the emitter tip so one can readily monitor the spray. The protective sleeve 108 is preferably slidably located on the emitter- emitter capillary 102. The protective sleeve 108 is preferably movable between an extended (or cover) position wherein it covers the emitter tip, and a retracted position wherein the emitter tip is exposed. When the emitter tip is exposed, it may be used for electrospray ionization. The emitter tip herein means the tip from which ions are produced when in use. The protective sleeve 108 thus covers and supports the emitter capillary 102 along at least a portion of its axis which includes the emitter tip.

[0030] The electrically conductive sheath 114 is coupled to a conductive nut 116. In various embodiments, the conductive nut can have an interior threaded portion consisting on a cavity and threading on the surface of the cavity. A plug-type end fitting 118 can be coupled to the proximal end of the emitter capillary 102 and extend from the cavity of the conductive nut. The emitter capillary 102 can be threaded through a sleeve 120, such as a PEEK sleeve, and the sleeve 120 and the emitter capillary 102 can be held in place relative to the conductive nut 116 with ferrule 122.

[0031] A spring 124 is further provided inside the electrically conductive sheath 114, positioned in a space between the conductive nut 116 and the protective sleeve 108. The spring 124 acts upon the base of the protective sleeve to bias the protective sleeve 108 to force it out of the electrically conductive sheath 114. The length of the sleeve 108 and its extension out of the sheath 114 is sufficient to cover the tip of the emitter capillary 102 and act to protect it against damage. A part of the main body 110 of the protective sleeve 108 protrudes outside the sheath 114 and thereby covers the emitter. The extent of travel of the sleeve 108 out of the sheath 114 is restricted by a reduced internal diameter at the end of the sheath 114 that stops the wider diameter base 112 of the sleeve. If aforce is applied to the sleeve 108 to push the sleeve 108 hackwards into the sheath 1 14, the spring 124 becomes compressed and the tip of the emitter capillary 102 becomes exposed and ready for use.

[0032] The spring is provided in contact with the protective sleeve to bias the sleeve towards its extended position. The spring is preferably in contact with the base of the protective sleeve. In this way, the spring, upon activation, is able to force the sleeve to cover the emitter tip when it is required to be protected. The spring also allows the sleeve to be retracted from the emitter tip when the integrated system is assembled with an instrument for mass spectrometric analysis. To enable this retraction, preferably the spring is forced into a compressed state, e.g. by pushing the sleeve towards the spring. The spring biases the sleeve to the extended position such that the sleeve adopts the extended or cover position when the sleeve does not have a sufficient force applied pushing it against the spring. The spring thereby enables the protective sleeve to cover the tip end of the emitter when the emitter is not required to be used such as when the integrated system is disassembled from an instrument for mass spectrometric analysis.

[0033] In various embodiments, an emitter cap 126 can cover an end of the electrically conductive sheath 114, and the emitter capillary 102 when not in use.

[0034] The electrically conductive sheath 114 can be enclosed within a holder having a high voltage contact point when the integrated system is in use. The holder can be a holder located on an instrument, e.g. for mass spectrometric analysis. The electrically conductive sheath 114 provides an electrical connection to enable the emitter to receive a high voltage. The sheath may provide an electrical connection to the emitter capillary 102 either directly or via one or more intermediate electrically conductive bodies, e.g. the protective sleeve 108 or the fitting. The electrically conductive sheath 114 has a recess in the form of a circumferential groove 128 in its outer surface for making an electrical contact with a high voltage contact, e.g. a contact ball forming an electrical path between the high voltage contact and a junction within the fitting.

[0035] In various embodiments, coupling with a laboratory apparatus, for example a mass spectrometer, becomes easier. Additionally, an exact and repeatable positioningprocess of the replaceable emitter 100 relatively to the frame can be guaranteed by shaping the electrically conductive sheath 114 to a shape that provides a close or tight fit in a receiving holder on the laboratory apparatus. The ease and accuracy of the positioning may be further enhanced by use of shapes that by design help lock the two items into a given position (e.g. by way of convex / concave mating surfaces, magnets or spring loads).

[0036] The column portion 200 includes a capillary column 202. The capillary column can include a stationary phase for performing chromatographic separation. Preferably, the column portion is an LC column, e.g. HPLC column. The LC column may be used with various flow rates, e.g. down to as low as nano-LC flow rates, i.e. 100 nL / min or less.

[0037] The capillary column 202 can be embedded in the molding material 206. The molding material 206 comprises a plastic material, for example, a thermoplastic material, for example, polyamide and polyurethane based MACROMELT material. Suitable methods to embed the assembly are described in the applicant’s patent US Pat 9302415.

[0038] The capillary column 202 of the column portion 200 is coiled into a loop 204 comprising multiple column windings to increase the separation length. This enables space saving since it allows a column to take up less space than if it were laid straight and it permits different column lengths to be used in the same design of integrated system, i.e. by changing the number of windings in the coil. Coiling the column further makes the column compact and able to fit into a small volume that may more easily be temperature controlled by a heating element than if it were laid straight and would occupy an elongated, typically long, space. In various embodiments, the heating element can be an integrated heating element, such as a resistive wire coiled along with the capillary column 202 in the loop 204. Alternatively, the heating element can be an external heating element that attaches to the column portion 200, such as by covering the loop 204. In order to meet the most relevant requirements in relation to the operation of the column, the separation column may be equipped with one or more embedded components of: aheating and / or cooling element and a thermal sensor in close proximity or contact with the column and preferably embedded in the molding material 206.

[0039] A proximal end 208 of the capillary column 202 is provided with fitting 210, e.g. for connection to an injector or other HPLC components. The fitting 210 can include a plug-type end fitting 216. Additionally, a distal end 212 of the capillary column 202 is provided with a receiving fitting 214 for joining with the plug-type fitting 118 of the replaceable emitter 100. In various embodiments, the receiving fitting 214 can include an exterior threaded surface to engage with the interior threaded portion of the conductive nut. Additionally, the receiving fitting 214 can include a central bore for receiving the plug-type end fitting 118. Fitting 210 and receiving fitting 214 can be at least partially exposed and not covered by the molding material 206.

[0040] When coupling the replaceable emitter 100 with the column portion 200, plug-type fitting 118 can slide into the interior cavity of receiving fitting 214 while receiving fitting 214 threadingly engages with conductive nut 116. In various embodiments, the receiving fitting can be inserted into the cavity of the conductive nut 116 surrounding the plug-type fitting while the exterior threaded surface of the receiving fitting 214 threadingly engages with the threading on the surface of the cavity of the conductive nut. The receiving fitting 214 can include a conductive stop 218 and, during coupling, the plug-type fitting 118 can abut the conducting stop 218. The column portion 200 can be assembled such that the capillary column 202 abuts the conductive stop 218 on the opposite side from the plug-type fitting 118. The conductive stop 218 can include a through hole to allow liquid to flow from the capillary column 202 to the emitter capillary 102. The through hole can be sized to minimize dead volume, generally being similar to the inner diameter of the capillary column 202 and the emitter capillary 102 to avoid the accumulation of liquid in the through hole.

[0041] When the replaceable emitter 100 is coupled to the column portion 200, the proximal end 106 of the emitter capillary 102 abuts the conductive stop 218 on one side and the capillary column 202 abuts the conductive stop 218 on the other side, providing a fluid connection between the emitter capillary 102 and the capillary column 202 by wayof a through hole in the conductive stop 218. The electrical path for applying the high voltage to the liquid flowing through the emitter capillary 102 can include the electrically conductive sheath 114, the conductive nut 116, and the receiving fitting 214 of the column portion 200, and the conductive stop 218. The liquid flowing through the emitter capillary 102 can carry the high voltage to the distal end 104 to enable electrospray of the liquid.

[0042] The plastic molding 206 provides rigidity to the system, as well as provides a shield against a user disassembling or damaging, intentionally or by accident, the fittings, HPLC column and emitter. In various embodiments, the plastic molding can be formed as a on the column portion 200. In other embodiments, the plastic molding 206 can be formed separately and placed over the column portion 200. For example, the plastic molding can be two parts that join together to surround the column portion 200.

[0043] The plastic molding 206 covers and protects the column portion 200. The electrically conductive 114 and the protective sleeve 108 protect the emitter capillary 102. An emitter cap 152 can cover the electrically conductive sheath when not in use. It will be appreciated from the description that the assembly of the replaceable emitter 100 and column portion 200 thus forms as a type of cartridge for use with an instrument, e.g. mass spectrometer, while the replaceable emitter 100 and column portion 200 can be disconnected and replaced individually.

[0044] In order to facilitate identification of the replaceable emitter 100 and column portion 200, identification tags such as a radio frequency identification tag (RFID) can be embedded in the replaceable emitter 100 and column portion 200.

[0045] In manufacturing the column portion 200, plastifying the plastic material that is used for embedding the column portion 200 may be achieved in various ways, preferably by heating the plastic material beyond the softening temperature for bringing it in its softening range and making it soft. In a preferred embodiment the entire column and at least a portion of the fittings are surrounded by the plastic material. The plastic material may be provided as a plastic molding part. The molding part may be a pre-formed part adapted to the shape of the integrated separation column and of the forming tool.

[0046] It is important to emphasize that preferred embodiments of the present invention are also directed to column portion protected by a plastic material, irrespective of the method used for the embedment in the plastic material. The column portion may in agreement with the other described embodiments of the present invention further comprise one or more of: an RFID-tag, heating / cooling elements and thermo sensor, a high-voltage contact point for the electrospray emitter, counter electrode(s) with a geometry that benefits definition of the field lines around the electrospray emitter, and channels for gas flow embedded in the plastic material.

[0047] The plastic embedding also renders physical strength to some otherwise rather fragile components that are prone to be damaged through everyday usage in laboratory environments. Nano-LC columns are frequently and advantageously made from a piece of silica glass tubing where said tubing typically is 10 mm to 1000 mm long but has an outer diameter of around 300 pm and hence the tubing can easily break. Typically, such silica glass tubing has an outer polymer lining of a few micrometers thickness that renders some strength, but the glass tubing is still easily broken. Similarly, the emitter is made from a very narrow piece of metal or glass tubing and can readily be damaged by contact with other items. The plastic embedding described herein makes the integrated column robust and durable such that they cannot readily break by accident. The protection of the column and emitter includes protection from physical strains, twists, bends as well as the pressure of the liquid inside the tubing whose thin walls are made several fold thicker by the plastic matrix being in direct (chemical) contact with the outer surface of the tubing.

[0048] The chromatographic retention times that are observed for the individual analytes are highly dependent on the temperature at which the separation takes place. Slight variation in temperature can lead to pronounced shifts in retention times and in order to obtain reproducible data, it is often sought to maintain stable ambient temperatures for the column. NanoLC columns — by virtue of their small diameters — canreadily exchange heat with the surrounding air. This is however prevented by the plastic matrix which provides thermal insulation of the columns and therefore assists in maintaining stable column temperatures.

[0049] While the present teachings are described in conjunction with various embodiments, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those of skill in the art.

[0050] Further, in describing various embodiments, the specification may have presented a method and / or process as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and / or process should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the various embodiments.

Claims

WHAT IS CLAIMED IS:

1. An integrated system for liquid separation and electrospray ionization, comprising: a replaceable emitter including: an emitter capillary with an emitter tip; a conductive sheath; a conductive nut electrically coupled to the conductive sheath; and a plug-type fitting; and a column portion including: a capillary column; a plastic molding encasing the capillary column; a receiving fitting for receiving the plug-type fitting and threadingly engage with the conductive nut; and a conductive stop.

2. The integrated system of claim 1, wherein the conductive sheath is configured to couple to a high voltage contact.

3. The integrated system of claim 2, wherein the conductive sheath has a circumferential groove for engaging with a contact ball of the high voltage contact.

4. The integrated system of claim 1, wherein the receiving fitting is electrically coupled to the conductive stop, and engagement of the receiving fitting and the conductive nut form an electrical contact between the conductive nut and the receiving fitting providing an electrical path to connect the high voltage contact with fluid passing through the conductive stop.

5. The integrated system of claim 1, wherein the electrically conductive nut includes an interior threaded portion with a cavity and the plug-type fitting extends from the cavity.

6. The integrated system of claim 5, wherein the receiving fitting includes an exterior threaded surface and a central bore the exterior threaded surface is configuredto engage with the interior threaded portion of the cavity and the central hore is configured to receive the plug-type end fitting.

7. The integrated system of claim 5 wherein the emitter capillary includes a porous matrix.

8. A replaceable emitter of an integrated system for liquid separation and electrospray ionization, comprising: an emitter capillary with an emitter tip; a conductive sheath with a circumferential groove configured to electrically couple to a high voltage contact; a conductive nut electrically coupled to the conductive sheath, the conductive nut including an interior threaded portion consisting of a cavity and a threading on the surface of the cavity; and a plug-type fitting extending through the cavity.

9. The replaceable emitter of claim 8 wherein the emitter capillary includes a porous matrix.

10. The replaceable emitter of claim 8 wherein the conductive nut is configured to thrcadingly engage with a column portion of the integrated system.

11. The replaceable emitter of claim 8, wherein engagement with the column portion provides an electrical path between the high voltage contact and the column portion.

12. A column portion of an integrated system for liquid separation and electrospray ionization, comprising: a capillary column with a stationary phase; a plastic molding encasing the capillary column; a receiving fitting including an exterior threaded surface and a central bore for receiving a plug-type fitting; and a conductive stop.

13. The column portion of claim 12, wherein the receiving fitting is configured to thrcadingly engage with a replaceable emitter of the integrated system and form an electrical contact between the replaceable emitter and the receiving fitting.

14. The column portion of claim 13, wherein the receiving fitting is electrically coupled to the conductive stop, and engagement of the receiving fitting and the replaceable emitter provides an electrical path between the replaceable emitter and fluid passing through the conductive stop.

15. The column portion of claim 13, wherein exterior threaded surface of the receiving fitting is configured to threadingly engage with an interior threaded portion of the replaceable emitter.

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