Diesel gas chromatography-mass spectrometry analysis pretreatment device

Abstract

This invention discloses a diesel gas chromatography-mass spectrometry (GC-MS) pretreatment device, comprising: N reagent bottles, M solid-phase extraction (SPE) columns, and a support structure, where N = 2 or 3. The M SPE columns are fixed to the support structure. The N reagent bottles are used to load different eluents. Each reagent bottle is connected to one end of M pipes, and the other end of each reagent bottle's M pipes is connected to one SPE column. Each SPE column is connected to the N reagent bottles via N pipes. A peristaltic pump is installed on each pipe to control the rate at which eluent is introduced into the SPE column. This diesel gas chromatography-mass spectrometry (GC-MS) pretreatment device can operate mechanically, utilizing the peristaltic pump to control the eluent elution rate and reduce errors in results caused by increased dead volume.

Description

Technical Field

[0001] This utility model belongs to the field of diesel gas chromatography-mass spectrometry analysis technology, specifically relating to a diesel gas chromatography-mass spectrometry analysis pretreatment device. Background Technology

[0002] Polycyclic aromatic hydrocarbons (PAHs) are a class of aromatic hydrocarbons composed of two or more benzene rings. Due to their high toxicity and carcinogenicity, PAHs have adverse effects on the environment and human health. Environmental pollution caused by PAHs is increasingly attracting attention, and they have become a priority for monitoring in many countries worldwide. The PAH content in diesel fuel is one of the control indicators specified in diesel fuel standards and is also an important indicator for evaluating the cleanliness of diesel fuel.

[0003] Gas chromatography-mass spectrometry (GC-MS) is a widely used technique for the detection of polycyclic aromatic hydrocarbons (PAHs). The advantages of GC-MS lie in its ability to simultaneously detect multiple PAH compounds, exhibiting high sensitivity and selectivity. Solid-phase extraction (SPE) is a physical separation process occurring between the stationary and mobile phases. It leverages the differences in the distribution and adsorption properties of the analyte and sample matrix on the stationary phase to achieve efficient separation of various hydrocarbon compounds. According to NB / SH / T0606 "Mass Spectrometry Method for Determination of Hydrocarbon Composition in Middle Distillate Fractions," before determining PAHs in diesel fuel using GC-MS, a solid-phase extraction column is required to separate the PAH standard from the saturated hydrocarbons, aromatics, and fatty acid methyl ester components in the diesel sample. This separation is followed by standard validation and determination of the PAH content in the sample.

[0004] Currently, the separation of components is entirely done manually. When separating the three components, different researchers have different judgments on the separation points, inconsistent eluent replacement times, and differences in elution rate control, resulting in poor reproducibility of the separation results. In addition, the pretreatment of a single sample takes about 20 minutes, making it difficult to handle large-scale, multi-batch testing tasks with time constraints. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a diesel gas chromatography-mass spectrometry (GC-MS) pretreatment device. Its working principle is consistent with that of manual component separation, but compared to manual operation, it offers advantages such as faster processing speed, higher efficiency, and greater safety. This diesel GC-MS pretreatment device can simultaneously pretreat multiple (4-10) samples, not only meeting the requirements of standards but also improving the pretreatment speed of standard substances and samples, reducing human error in sample pretreatment, and minimizing reagent volatilization and contact between laboratory personnel and toxic reagents. It is a reliable, green, and safe device.

[0006] The objective of this utility model is achieved through the following technical solution.

[0007] A diesel fuel gas chromatography-mass spectrometry (GC-MS) pretreatment device includes: N reagent bottles, M solid-phase extraction (SPE) columns, and a support structure, where N = 2 or 3. The M SPE columns are fixed on the support structure. The N reagent bottles are used to load different eluents. Each reagent bottle is connected to one end of M pipes. The other end of each of the M pipes in each reagent bottle is connected to a SPE column. Each SPE column is connected to the N reagent bottles through N pipes. A peristaltic pump is installed on each pipe to control the rate at which eluent is introduced into the SPE column.

[0008] In the above technical solution, M is an integer between 4 and 10.

[0009] In the above technical solution, the support structure includes: a frame, a first support, and two first slide rails. The first support is used to place M solid phase extraction columns. The length direction of the first support is parallel to the X-axis. The plane containing the X-axis and Y-axis is a horizontal plane. The two first slide rails are parallel and respectively arranged along the Z-axis direction. The two first slide rails are fixed on the frame. A first slider is installed on each first slide rail. Each first slider is respectively connected to one end of the first support, so that the first support can move along the Z-axis direction on the first slide rail.

[0010] M horizontally arranged third slide rails are fixed on the frame below the solid phase extraction column. Each solid phase extraction column is directly opposite a third slide rail. Each third slide rail is set along the Y-axis. N third sliders are installed on each third slide rail, and a collection bottle is placed on each third slider. The N×M third sliders on the M third slide rails are arranged in a rectangular array on the horizontal plane.

[0011] In the above technical solution, M solid phase extraction columns are arranged along the X-axis and fixed on the first support.

[0012] In the above technical solution, M first through holes are formed on the first support. The diameter of the first through holes is the same as the diameter of the solid phase extraction column. One solid phase extraction column is placed in each first through hole. The solid phase extraction column has a limiting protrusion along its circumference and the protrusion is limited above the first support.

[0013] In the above technical solution, the top surface of the solid-phase extraction column is open, and the support structure also includes: a second bracket located above the solid-phase extraction column, the two ends of the second bracket being fixed to two first sliders respectively, a cover of the solid-phase extraction column being fixed on the second bracket above each solid-phase extraction column, each cover facing the open of a solid-phase extraction column, N connecting tubes penetrating the cover, each connecting tube being connected to one of the pipes, and the solid-phase extraction column being connected to N reagent bottles through the N connecting tubes on its cover;

[0014] A second slide rail is fixed on each first slide rail and is arranged along the Z-axis. A second slide rail is installed on each second slide rail. Both ends of the first bracket are connected to the second slide rail, so that after the first bracket slides upward along the second slide rail, the cover covers the opening of the solid phase extraction column opposite to it, and after the first bracket slides downward along the second slide rail, the cover leaves the solid phase extraction column.

[0015] In the above technical solution, a rotating structure is installed between the first bracket and the second slider so that the first bracket can rotate 30 to 60 degrees about the X-axis.

[0016] In the above technical solution, the support structure also includes: N third brackets and two fourth slide rails, each fourth slide rail is equipped with N fourth sliders, each third bracket is arranged along the X-axis direction, the two fourth slide rails are arranged along the Y-axis direction and fixed on the frame, and the two ends of each third bracket are fixed to the two fourth sliders so that the third bracket can slide along the fourth slide rail.

[0017] M third through holes are formed on each third support, and one collection bottle is placed in each through hole to keep N×M collection bottles arranged in a rectangular array on a horizontal plane.

[0018] In the above technical solution, a base is fixedly mounted on the third slider, and the upper part of the base is used to embed a collection bottle.

[0019] In the above technical solution, the third bracket is located above the base.

[0020] The beneficial effects of this utility model are as follows:

[0021] 1. The diesel gas chromatography-mass spectrometry pretreatment device of this invention can operate mechanically, is applicable to various solid phase extraction columns, and can use a peristaltic pump to control the elution rate of the eluent and reduce the error in the results caused by the increase of dead volume.

[0022] 2. The support structure of this utility model realizes full automation of the process from "solvent switching" to "sample collection" without manual intervention, improving efficiency several times over, and is particularly suitable for the detection needs of large batches of samples. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the diesel gas chromatography-mass spectrometry pretreatment device according to Embodiment 1 of this utility model;

[0024] Figure 2 This is a schematic diagram of the diesel gas chromatography-mass spectrometry pretreatment device according to Embodiment 2 of this utility model;

[0025] Figure 3 This is a cross-sectional view of the diesel gas chromatography-mass spectrometry pretreatment device of Embodiment 3 of this utility model;

[0026] Figure 4 This is a cross-sectional view of the diesel gas chromatography-mass spectrometry pretreatment device of Embodiment 3 of this utility model;

[0027] Figure 5 This is a cross-sectional view of the diesel gas chromatography-mass spectrometry pretreatment device of Embodiment 3 of this utility model;

[0028] Figure 6 This is a top view of the diesel gas chromatography-mass spectrometry pretreatment device of Embodiment 3 of this utility model.

[0029] Wherein, 1: reagent bottle, 2: solid phase extraction column, 2-1: protrusion, 3: support structure, 3-1: frame, 3-2: first support, 3-3: base, 3-4: first slider, 3-5: third slide rail, 3-6: second support, 3-7: cover, 3-8: connecting tube, 3-9: third slider, 3-10: third support, 3-11: fourth slide rail, 3-12: second slider, 4: peristaltic pump, 5: collection bottle. Detailed Implementation

[0030] The technical solution of this utility model will be further described below with reference to the accompanying drawings and embodiments.

[0031] In the technical solution of this invention, the X-axis represents the left-right direction; the Y-axis represents the front-back direction; and the Z-axis represents the up-down direction.

[0032] Example 1

[0033] like Figure 1As shown, a diesel gas chromatography-mass spectrometry (GC-MS) pretreatment device includes: N reagent bottles 1, M solid-phase extraction columns 2, and a support structure 3, where N = 2 or 3. The M solid-phase extraction columns 2 are fixed on the support structure 3. The N reagent bottles 1 are used to load different eluents. Each reagent bottle 1 is connected to one end of M pipes (the M pipes corresponding to the N reagent bottles 1 are different, that is, the diesel gas chromatography-mass spectrometry pretreatment device has N sets of "M pipes"). The other end of each of the M pipes in each reagent bottle 1 is connected to a solid-phase extraction column 2. Each solid-phase extraction column 2 is connected to the N reagent bottles 1 through N pipes. The top surface of each solid-phase extraction column 2 is open, and a cover 3-7 is installed on the open.

[0034] Each cap 3-7 has N connecting tubes 3-8 running through it. Each connecting tube 3-8 is used to connect to a pipe. The solid phase extraction column 2 is connected to N reagent bottles 1 through the N connecting tubes 3-8 on its cap 3-7. A peristaltic pump 4 is installed on each pipe to control the rate at which the eluent is introduced into the solid phase extraction column 2. M is an integer from 4 to 10.

[0035] The supporting structure is a standard bracket.

[0036] When the sample contains only saturated hydrocarbons and aromatic hydrocarbons, i.e., two eluents are required for elution, N=2. When the sample contains saturated hydrocarbons, aromatic hydrocarbons, and fatty acid methyl esters, i.e., three eluents are required for elution, N=3.

[0037] Taking N=3 as an example, different eluents are filled into the three reagent bottles 1 respectively. Eluent ①: n-hexane, eluent ②: a mixture of dichloromethane and n-hexane (the volume ratio of dichloromethane to n-hexane is 1:1), eluent ③: a mixture of dichloromethane and ethanol (the volume ratio of dichloromethane to ethanol is 1:1).

[0038] M solid-phase extraction columns 2 operate simultaneously, and the working process of each solid-phase extraction column 2 includes the following steps:

[0039] Step 1: Set the peristaltic pump 4 to a speed of 2 mL / min and introduce 0.5 mL of eluent ① into the solid phase extraction column 2 to wet the solid phase extraction column 2;

[0040] Step 2: Open the cover 3-7, add 100 μL of sample (i.e. diesel) to the solid phase extraction column 2, and close the cover 3-7.

[0041] Step 3: Place a collection bottle 5 below the solid-phase extraction column 2, so that the bottom of the solid-phase extraction column 2 is suspended and located inside the collection bottle 5. Set the peristaltic pump 4 to a speed of 2 mL / min, and introduce 2 mL of eluent ① into the solid-phase extraction column 2. Then introduce 0.5 mL of eluent ② into the solid-phase extraction column 2 at a rate of 2 mL / min to perform the first elution. The saturated hydrocarbon component is collected in the collection bottle 5.

[0042] Step 4: Replace with a new collection bottle 5, set the peristaltic pump 4 to a speed of 2 mL / min, introduce 2 mL of eluent ② into the solid phase extraction column 2, and then introduce 0.5 mL of eluent ③ into the solid phase extraction column 2 at a speed of 2 mL / min for a second elution. The aromatic component is collected in the collection bottle 5.

[0043] Step 5: Replace with a new collection bottle 5, set the peristaltic pump speed to 2 mL / min, and introduce 6 mL of eluent ③ into the solid phase extraction column 2 for a third elution. Collect the fatty acid methyl ester fraction in the collection bottle 5.

[0044] Following the steps above, the diesel fuel gas chromatography-mass spectrometry (GC-MS) pretreatment is completed, and the collected samples can be used for further injection and analysis. Generally, each sample requires two parallel experiments. When M=4, the diesel fuel GC-MS pretreatment device can test two samples simultaneously.

[0045] Before using the diesel gas chromatography-mass spectrometry (GC-MS) pretreatment device, the pretreatment time for a single sample was 3.1 hours, and the total time for a single sample to complete pretreatment, instrument analysis, result processing, and report generation was 7.1 hours. With the diesel gas chromatography-mass spectrometry (GC-MS) pretreatment device, the pretreatment time for a single sample is reduced to 0.8 hours, and the total time for a single sample to complete pretreatment, instrument analysis, result processing, and report generation is reduced to 4.6 hours. This optimizes the diesel sample detection process, saves sample pretreatment time, avoids errors that are easily caused by human operation, and improves detection efficiency.

[0046] Based on this, the improvement in work efficiency has also led to an increase in economic benefits: from May to August 2024, the number of diesel polycyclic aromatic hydrocarbon samples tested was 21 batches. After using this diesel gas chromatography-mass spectrometry pretreatment device, from February to May 2025, the number of diesel polycyclic aromatic hydrocarbon samples tested was 58 batches, an increase of 176.2% compared to before. Due to the reduction in pretreatment time, personnel costs were also reduced.

[0047] Example 2

[0048] A diesel fuel gas chromatography-mass spectrometry (GC-MS) pretreatment device is basically the same as in Example 1, except for the support structure 3. This example proposes a more automated support structure. Figure 2As shown, the support structure 3 includes: a frame 3-1, a first support 3-2, and two first slide rails (not shown in the figure). The first support 3-2 is used to place M solid-phase extraction columns 2. The length direction of the first support 3-2 is parallel to the X-axis. The M solid-phase extraction columns 2 are arranged along the X-axis and fixed on the first support 3-2. Specifically, the first support 3-2 has M first through holes, the diameter of which is the same as the diameter of the solid-phase extraction column 2. One solid-phase extraction column 2 is placed in each first through hole. The solid-phase extraction column 2 has a limiting protrusion 2-1 along its circumference, and the protrusion 2-1 is limited above the first support 3-2.

[0049] The plane containing the X-axis and Y-axis is a horizontal plane. The two first slide rails are parallel and set along the Z-axis direction respectively. The two first slide rails are fixed on the frame 3-1. A first slider 3-4 is installed on each first slide rail. Each first slider 3-4 is connected to one end of the first bracket 3-2 so that the first bracket 3-2 can move along the Z-axis direction on the first slide rail.

[0050] M horizontally arranged third slide rails 3-5 are fixedly mounted on the frame 3-1 below the solid phase extraction column 2. Each solid phase extraction column 2 is directly opposite one third slide rail 3-5. Each third slide rail 3-5 is arranged along the Y-axis. N third sliders 3-9 are installed on each third slide rail 3-5, and a collection bottle 5 is placed on each third slider 3-9. The N×M third sliders 3-9 on the M third slide rails 3-5 are arranged in a rectangular array on the horizontal plane. Preferably, a base 3-3 is fixedly mounted on the third slider 3-9, and the upper part of the base 3-3 is used to embed a collection bottle 5.

[0051] The steps for replacing the collection bottle 5 during each elution step include: sliding the first slider 3-4 upwards to remove the bottom of the solid-phase extraction column 2 from the collection bottle 5; placing one collection bottle on each of the N×M third sliders 3-9; sliding the collection bottle 5 to be replaced along the Y-axis until the new collection bottle 5 is directly below the solid-phase extraction column 2; and sliding the first slider 3-4 downwards to reposition the bottom of the solid-phase extraction column 2 back into the collection bottle 5. This support structure 3 makes replacing the collection bottle 5 more convenient, eliminating the need to pick up each solid-phase extraction column 2 individually, further saving processing time and improving work efficiency.

[0052] Example 3

[0053] like Figures 3-5 As shown, a diesel gas chromatography-mass spectrometry analysis pretreatment device, based on Example 2, further includes a second support 3-6 located above the solid phase extraction column 2, with the two ends of the second support 3-6 respectively fixed to two first sliders 3-4, and the cover 3-7 of each solid phase extraction column 2 fixed to the second support 3-6.

[0054] A second slide rail arranged along the Z-axis is fixedly mounted on each first slider 3-4, and a second slider 3-12 is mounted on each second slide rail. Both ends of the first support 3-2 are connected to the second slider 3-12, so that after the first support 3-2 slides upward along the second slide rail, the cover 3-7 covers the opening of the solid phase extraction column 2 opposite to it (e.g., Figure 4 As shown), after the first support 3-2 slides down along the second slide rail, the cover 3-7 leaves the solid phase extraction column 2 (as shown). Figure 5 (As shown).

[0055] A rotating structure (not shown in the figure) is installed between the first support 3-2 and the second slider 3-12, so that the first support 3-2 can rotate 30 to 60 degrees about the X-axis. The sample can be loaded through the rotating structure.

[0056] The support structure 3 also includes: N third brackets 3-10 and two fourth slide rails 3-11. The third brackets 3-10 are located above the base 3-3. Each fourth slide rail 3-11 is equipped with N fourth sliders (not shown in the figure). Each third bracket 3-10 is arranged along the X-axis direction, and the two fourth slide rails 3-11 are arranged along the Y-axis direction and fixed to the frame 3-1. The two ends of each third bracket 3-10 are fixed to the two fourth sliders so that the third bracket 3-10 can slide along the fourth slide rail 3-11.

[0057] M third through holes are formed on each third support 3-10, and a collection bottle 5 is placed in each through hole to maintain N×M collection bottles 5 in a rectangular array on the horizontal plane (e.g., Figure 6 (As shown). The third support 3-10 can improve the stability of the collection bottle.

[0058] In this embodiment, the step of adding a sample to the solid-phase extraction column 2 is more convenient. First, slide the first slider 3-4 upward to lift the solid-phase extraction column 2, then slide the second slider 3-12 downward to separate the solid-phase extraction column 2 from the cover 3-7. Rotate the first support 3-2 through the rotating structure to tilt the solid-phase extraction column 2, add diesel fuel into the solid-phase extraction column 2, and after adding the sample, rotate the first support 3-2 in the opposite direction to restore the solid-phase extraction column 2 to a vertical position. Slide the second slider 3-12 upward to cover the corresponding solid-phase extraction column 2 with the cover 3-7.

[0059] The process of replacing the collection bottle 5 at each elution step is more convenient. Slide the first slider 3-4 upward to separate the solid-phase extraction column 2 and the collection bottle 5. Slide the third support 3-10 along the fourth slide rail 3-11 to move the new collection bottle 5 directly below the solid-phase extraction column 2. Slide the first slider 3-4 downward to suspend the bottom of the solid-phase extraction column 2 inside the collection bottle 5, eliminating the need to slide each third slider 3-9 separately.

[0060] Using the above-mentioned diesel gas chromatography-mass spectrometry (GC-MS) pretreatment device, the diesel gas chromatography-mass spectrometry (GC-MS) pretreatment process is mechanized, making the operation more convenient and faster, further improving efficiency, reducing human error, and freeing up manpower.

[0061] The present invention has been described above by way of example. It should be noted that, without departing from the core of the present invention, any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort fall within the protection scope of the present invention.

Claims

1. A device for the pretreatment of diesel for gas chromatography-mass spectrometry analysis, characterized in that, include: N reagent bottles (1), M solid-phase extraction columns (2) and support structure (3), N = 2 or 3. The M solid-phase extraction columns (2) are fixed on the support structure (3). The N reagent bottles (1) are used to load different eluents. Each reagent bottle (1) is connected to one end of M pipes. The other end of each reagent bottle (1)'s M pipes is connected to a solid-phase extraction column (2). Each solid-phase extraction column (2) is connected to the N reagent bottles (1) through N pipes. A peristaltic pump (4) is installed on each pipe to control the speed at which eluent is introduced into the solid-phase extraction column (2).

2. The diesel gas chromatography mass spectrometry pre-treatment device according to claim 1, characterized in that, M is an integer between 4 and 10.

3. The diesel gas chromatography mass spectrometry pre-treatment device according to claim 1 or 2, characterized in that, The support structure (3) includes: a frame (3-1), a first support (3-2), and two first slide rails. The first support (3-2) is used to place M solid-phase extraction columns (2). The length direction of the first support (3-2) is parallel to the X-axis. The plane containing the X-axis and Y-axis is a horizontal plane. The two first slide rails are parallel and respectively set along the Z-axis direction. The two first slide rails are fixed on the frame (3-1). A first slider (3-4) is installed on each first slide rail. Each first slider (3-4) is respectively connected to one end of the first support (3-2) so that the first support (3-2) can move along the Z-axis direction on the first slide rail. M horizontally arranged third slide rails (3-5) are fixed on the frame (3-1) below the solid phase extraction column (2). Each solid phase extraction column (2) is directly opposite a third slide rail (3-5). Each third slide rail (3-5) is arranged along the Y-axis. N third sliders (3-9) are installed on each third slide rail (3-5). A collection bottle (5) is placed on each third slider (3-9). The N×M third sliders (3-9) on the M third slide rails (3-5) are arranged in a rectangular array on the horizontal plane.

4. The diesel gas chromatography mass spectrometry pre-treatment device according to claim 3, characterized in that, M solid-phase extraction columns (2) are arranged along the X-axis and fixed on the first support (3-2).

5. The diesel gas chromatography-mass spectrometry pretreatment apparatus according to claim 4, characterized in that, M first through holes are formed on the first support (3-2). The diameter of the first through hole is the same as the diameter of the solid phase extraction column (2). One solid phase extraction column (2) is placed in each first through hole. The solid phase extraction column (2) has a limiting protrusion (2-1) formed along its circumference. The protrusion (2-1) is limited above the first support (3-2).

6. The diesel gas chromatography mass spectrometry pre-treatment device according to claim 5, characterized in that, The top surface of the solid-phase extraction column (2) is open. The support structure (3) also includes: a second bracket (3-6) located above the solid-phase extraction column (2). The two ends of the second bracket (3-6) are fixed to two first sliders (3-4) respectively. The cover (3-7) of the solid-phase extraction column (2) is fixed on the second bracket (3-6) above each solid-phase extraction column (2). Each cover (3-7) is directly opposite the opening of a solid-phase extraction column (2). N connecting tubes (3-8) pass through the cover (3-7). Each connecting tube (3-8) is connected to a pipe. The solid-phase extraction column (2) is connected to N reagent bottles (1) through the N connecting tubes (3-8) on its cover (3-7). A second slide rail is fixed on each first slide rail (3-4) and arranged along the Z-axis. A second slide rail (3-12) is installed on each second slide rail. Both ends of the first bracket (3-2) are connected to the second slide rail (3-12) so that after the first bracket (3-2) slides upward along the second slide rail, the cover (3-7) covers the opening of the solid phase extraction column (2) opposite to it, and after the first bracket (3-2) slides downward along the second slide rail, the cover (3-7) leaves the solid phase extraction column (2).

7. The diesel gas chromatography mass spectrometry pre-treatment device according to claim 6, characterized in that, A rotating structure is installed between the first bracket (3-2) and the second slider (3-12) so that the first bracket (3-2) can rotate 30 to 60 degrees about the X-axis.

8. The diesel gas chromatography mass spectrometry pre-treatment device according to claim 7, characterized in that, The support structure (3) also includes: N third brackets (3-10) and two fourth slide rails (3-11), each fourth slide rail (3-11) is equipped with N fourth sliders, each third bracket (3-10) is arranged along the X-axis direction, the two fourth slide rails (3-11) are arranged along the Y-axis direction and fixed on the frame (3-1), and the two ends of each third bracket (3-10) are fixed to the two fourth sliders so that the third bracket (3-10) can slide along the fourth slide rail (3-11); M third through holes are formed on each third support (3-10), and one collection bottle (5) is placed in each through hole to keep N×M collection bottles (5) arranged in a rectangular array on the horizontal plane.

9. The diesel gas chromatography-mass spectrometry pretreatment apparatus according to claim 8, characterized in that, A base (3-3) is fixed on the third slider (3-9), and the upper part of the base (3-3) is used to embed a collection bottle (5).

10. The diesel gas chromatography mass spectrometry pre-treatment device according to claim 9, characterized in that, The third bracket (3-10) is located above the base (3-3).

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