Anal. Chem. 1985, 57, 2229-2235
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Direct Sample Introduction System for Inductively Coupled Plasma Emission Spectrometric Detection in Microcolumn Liquid Chromatography Kiyokatsu Jinno,* Shoji Nakanishi, and Chuzo Fujimoto School of Materials Science, Toyohashi University of Technology, Toyohashi 440,Japan
To solve problems encountered In lnductlvely coupled plasma emlssion spectrometrlc detectlon combined with mlcrocolumn llquld chromatography, a “no-spray chamber” nebulizing system has been designed and Its performance has been demonstrated. Improvements In resoiutlon and sensitivlty have been observed wlth the newly developed system. To get reproduclble emlssion signals, the lower part of the sample Introduction tube of the plasma torch was heated to about 60-80 ‘C when an aqueous mobile phase was used for LC separatlons.
The coupling techniques of high-performance liquid chromatography (HPLC) to inductively coupled plasma atomic emission spectrometry (ICP-AES, ICP) offers new and attractive approaches for elemental analysis in a wide variety of compounds. The utilization of ICP as a detector for HPLC provides a powerful and versatile method for chromatographic separations. To date, the coupling of HPLC to the ICP has only been accomplished using conventional nebulizer, although a new attempt has recently been reported by Fassel et al. (1). Detection sensitivity under these conditions has generally been observed to be poorer when compared to conventional continuous sample flow conditions. This limitation has been attributed from the large dead volume and the loss of sample components eluted from HPLC column prior to entering a nebulizer unit. These problems will be a more serious in combining ICP with microcolumn HPLC (micro-LC), which has become popular recently (2-4), because of its smaller column volume than that of conventional HPLC columns. Therefore the authors have reported the modified cross-flow nebulizer for combining micro-LC with ICP and improved separation efficiency and sensitivity were observed compared to the previous methods (5-9). However, the system was insufficient for microcapillary LC, because microcapillary LC requires that the nebulizer provide higher efficiency and mass concentration than conventional HPLC. In an effort to solve these requirements, we have developed a direct sample introduction method just suitable to micro-LC combined with ICP detection. In this contribution, we will compare three sample introduction systems and draw a conclusion that the novel direct sample introduction which has a “no-spray chamber” is the best system to meet our final purpose, microcapillary LC with ICP detection. The potential of the system will also be demonstrated by some experimental separations.
EXPERIMENTAL SECTION The ICP system used was a Model ICAP-BOOS(Nippon-Jarrell Ash, Co., Ltd., Tokyo, Japan). The operating conditions of the ICP in micro-LC-ICP combination which gave the best results are shown in Table I. All chromatographic data by ICP were obtained with a 1-m Czerny-Turner monochromator, and the signal from a photomultiplier (HamamatsuPhotonics, Japan) was amplified and recorded on a strip-chart recorder. Aerosols were
Table I. ICP Conditions in Microcapillary LC-ICP System
operating conditions operating conditions frequency (MHz) power (kW) Ar gas flow rate (L/min) coolant gas plasma gas sample gas viewing height above coil (mm)
LC mobile phase toluene or chloroform water 27.12 2.4 16
20
1
3
0.45 5
15
generated pneumatically with a modified cross-flow nebulizer, as proposed in the previous papers (8,9),and three different spray chambers whose specificationsare as follows: (1)the nebulizing system as shown in Figure 1with the modified cross-flownebulizer and “no-spraychamber”;(2) a conventional ICP nebulizing system using the modified cross-flownebulizer and a spray chamber whose size is 31 mm i.d. X 82 mm long with a volume of 62 mL; (3) a conventionalICP nebulizing system using the modified cross-flow nebulizer and a spray chamber whose size is 31 mm i.d. X 164 mm long with a volume of 124 mL. The micro-LC instrumentationconsisted of a microfeeder MF-2 (Azuma Electric, Co., Ltd., Tokyo, Japan) as a pump and a micro loop injector ML-422 (Jasco, Tokyo, Japan, 0.3 p L ) for sample introduction to the LC system. The UV detector used was a Uvidec100-I11 (Jasco, Tokyo, Japan). All microchromatographic columns used in this study were prepared by the slurry technique in the laboratory. Column packings used were as follows: separation of a sample mixture of short alkyl chain alcohols was accomplished by a fused-silica capillary column (0.35 mm i.d. X 400 mm long) packed with Shodex KC-811 cation-exchangeresin (8 pm, Showa Denko, Co., Ltd., Tokyo, Japan); separation of a sample mixture of organometallic compounds (diethyldithiocarbamate complexes, DDTC) was performed by using a fusedsilica capillary column (0.35 mm i.d. X 230 mm long) packed with Develosil loO-5 (silica,Nomura Chemicals,Seto, Japan); separation of a shale oil (NBS SRM-1580) was done by using a fused-silica capillary column (0.5 mm i.d. X 600 mm long) packed with TSK Gel 1000-H (Toyo Soda, Co., Ltd., Tokyo, Japan). Distilled water was used as the mobile phase for the Shodex column,and toluene and chloroform were used for the Develosil column and for the TSK column, respectively. When the sample mixture of alcohols was chromatographed, the column was heated by a homemade column heater at 60 “C. All other chemicals used were commercially available products from many sources.
RESULTS AND DISCUSSION Interfacing between Micro-LC and ICP. In micro-LC, extracolumn band broadening has a severe influence on the column efficiency compared with that in conventional HPLC. Therefore, to minimize the extracolumn band broadening, the microcolumns were connected with the cross-flow nebulizer as shown in Figure 1, in which the “no-spray chamber” was used. That nebulizer has been described in previous papers (8,9). We have developed a direct connecting device for the microcapillary LC-ICP combination. For direct connection of the fused silica capillary columns to the nebulizer, a stainless
0003-2700/85/0357-2229$01.50/0 0 1985 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 12, OCTOBER 1985
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1 Figure 1. A schematic dlagram of direct Introduction microcapillary LC-ICP system: (1) fused-silica caplllary column; (2) LC effluent flow: (3) direct connecting device: (4) sample Ar gas flow: (5) device for Ar gas inlet: (6) bcdy of cross-flow nebulizer made of Teflon fluorocarbon resin: (7) plasma torch; (8) heater: (9) O-ring: (10) glass capillary: (P) nebulizing point.
P
Flgure 2. A schematic diagram of direct connecting device (no. 3 In Figure 1) for sample introduction to nebulizer: (1) device body: (2) O-ring: (3) fused-silica capillary column; (4) stationary phase: (5) connecting tube made of Teflon fluorocarbon resin: (6) quartz wool: (7) stainless steel capillary: (8) glass capillary: (P) nebullzlng polnt.
steel capillary (0.31 mm o.d., 0.13 mm i.d. X 25 mm long) was used as the intermediate tube through a glass capillary (0.32 mm i.d. X 20 mm long) which is the sample uptake tube for normal ICP operation. The same size stainless steel capillary extends close to the tip of the glass capillary where nebulization is accomplished, as shown in Figure 2. The total column effluent from the fused-silica capillary column is nebulized by the sample Ar gas flow over the capillary orifice (point P in Figure 1 and 2). System Performance. To investigate the effect of the sample Ar gas flow rate on emission intensity observed by the ICP system, the Shodex column was used with distilled water as the mobile phase, and the range of the sample Ar gas flow rate was varied from 0.3 L/min to 0.6 L/min. The flow rate of the mobile phase was also changed from 16 pL/min to 1 fiL/min, and three different nebulizing systems were used for evaluating the performance. The methanol solution, which contains 0.8 pg of methanol in water, was injected as the test probe into the column and the emission from the carbon atomic line at 247.86 nm was monitored. The effect of various sample gas flow rates on the emission intensity has been studied, where signals were recorded with changing viewing heights above the turns of the load coil between 5 mm and 25 mm, and the representative results under the following conditions are shown in Figure 3: mobile phase flow rates of 4 pL/min and 2 pL/min with “no-spray chamber” nebulizing system at 0.45 L/min of Ar sample gas flow rate. The spatial emission profiles of 247.86 nm carbon emission line were similar to the results described by Browner
5-
Flgure 3. Effect of viewing height on emlssion signal intensity of carbon atomic llne at 247.86 nm using “no-spray chamber” system: sample, methanol, 0.8 pg in water; sample Ar gas flow rate, 0.45 Llmin; mobile phase flow rate, (A) 4 pL/min, (B) 2 pL/min.
et al. (10). The carbon emission intensities decreased with increasing viewing height, but further research is necessary to explain the excitation mechanism more clearly. Figure 4 shows the results at the viewing point of 5 mm high above the load coil. The maximum emission intensity of carbon was observed at this 5 mm height. It appears that the maximum emission intensity was measured at around 0.45 L/min of the sample Ar gas flow rate, regardless of the flow rate of the mobile phase and the volume of the spray chamber. Similar results have been found in that the reduction in the diameter of the sample introduction tube to the nebulizer from 2.3 to 0.8 mm i.d. caused a shift in the maximum of the emission intensity observed to a lower Ar gas flow rate from 0.72 to about 0.47 L/min (11). The effect of the spray chamber volume on the signal intensity is also shown in Figure 4, where the results are illustrated with the chamber volume of 124 mL in Figure 4A, with the chamber volume of 64 mL in Figure 4B, and with “nospray chamber” in Figure 4C, respectively. As known, the spray chamber has a basic function in the nebulization processes; that is, it is the effective remover of sample aerosol droplets whose sizes are unsuitable diameters to be introduced into the plasma. Then, however, it unfortunately produces a mixing effect. While it is true that the function is effective for conventional ICP analysis, it produces rather worse effects on the efficiency of micro-LC separations in the case of direct connection of microcapillary columns to a nebulizer. The mixing chamber spoils the resolution of micro-LC because closely separated components could be remixed with each other in the spray chamber. On the other hand, the removal of unsuitable sample droplets reduces the sensitivity of the micro-LC-ICP system because of the loss of sample aerosols which should be transported into a plasma flame, due to adhering to the inner wall of the spray chamber and the sample introduction tube of the torch. Therefore it is expected that a more enhanced emission intensity will be observed with the smaller volume of a spray chamber. For that point, however, Hausler and Taylor (12) have reported that a spray chamber having “very small” volume did not eliminate waste solvent effectively; in their work, they reached the conclusion that the reason was that solvent eventually rose above the
ANALYTICAL CHEMISTRY, VOL. 57, NO. 12, OCTOBER 1985
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Figure 4. Effect of spray chamber volume on the emission signal intensity of carbon atomic line at 247.86 nm: chamber volume, (A) 124 mL, (B) 6 2 mL, (C) 0 mL; sample, methanol, 0.8 pg in water; water flow rate, (A) 16 pL/min, (B) 4 pL/min, (C) 1 fiL/min.
nebulizer outlet causing spurious results. Since the advantage of micro-LC techniques is smaller flow rates of the mobile phase on the order of microliters per minute, severe problems due to solvent nebulization should not occur. It has been observed that smaller spray chamber volume or "no-spray chamber" nebulization is more effective in micro-LC-ICP interfacing. With the reduction of the spray chamber volume, the signal intensity of the carbon emission line was enhanced; the intensity ratios are 1.4 and 1.7 for the 62 mL and 0 mL chambers, respectively, when the intensity observed with the 124-mL chamber is assumed to be unity. In addition, the remixing and the loss of the sample components separated by the microcolumn in the spray chamber will be expected to badly affect the performance and sensitivity of the micro-LC-ICP system. Peak Reproducibility in the No-Spray Chamber System. When aqueous mobile phase was used in the "no-spray chamber" system, nonreproducible signal intensity was observed during measurements. To clarify the reason of this nonreproducibility of signals, the injection of a 0.3-pL methanol solution (0.8 pg of methanol) was carried out, with water as the mobile phase, directly in the nebulizer without passing through the LC column in order to quickly and efficiently evaluate the performance of the nebulizing systems without the additional complicationsimposed by retention on the LC column. In addition, to make clear understanding of this phenomenon, experiments have been attempted where the lower part of the sample introduction tube of the plasma torch was heated by a nichrome heater. The effect of the heating on the intensity of the carbon emission line at 247.86 nm is shown in Figure 5, in which the transient signals to 0.8 pg of methanol are increased as a parameter of the temperature for multiple injections to the optimum. The optimum temperature range to get the best signal reproducibility is between 60 "C and 80 OC. As can be seen, the reproducibility seems to be getting worse with either an increase or a decrease in the temperature of the heater, and the reproducibility is significantly bad when the temperature is lower than the optimum. At higher temperatures, complete vaporization of methanol is achieved and some
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0
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Figure 5. Reproducibility of emission signal intensity with the use of water as mobile phase: sample, methanol, 0.8 pg in water; heater temperature, (A) room temperature, (B) 40 OC, (C) 60 OC, (D) 80 OC, (E) 100 OC.
quenching effects disturb the better emission measurements. At lower temperatures, the nebulization is relatively wet, which results in sticking aerosols to the inner wall of the sample introduction tube of the plasma torch and in leading to the problem of making droplets a t the wall by coagulation. The transport efficiency for the present nebulizing system without a spray chamber was determined by the use of a conventional silica gel tube method in order to assure system performance. The method utilized here essentially duplicated
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 12, OCTOBER 1985
Table 11. Transport Efficiency Measured by the Silica Gel Method" transport efficiency, % 62 mL 0 mL 0 mL r.teb r.tab r.t.* 60 "C
mobile phase flow rate for micro-LC, hL/min
124 mL
16
78.2 83.9
4
81.8 87.2
69.7 90.9
87.7 97.6
"Sample Ar gas flow rate, 0.45 L/min. Conventional ICP nebulizing with uptake rate of 0.48 L/min was measured as 6.0% of the transport efficiency with this method. *Room temperature. that of Schutyser and Janssens (13). The amount of aerosols sprayed by the cross-flow nebulizer was determined gravimetrically by the difference in the weight of the silica gel tube (10 mm i.d. X 18.5 cm long) before and after adsorbing aerosols. The transport efficiency is defined as the ratio of the amount of aerosols adsorbed onto silica gel and the amount of liquid nebulized by the cross-flow nebulizer. The data of the transport efficiency expressed in percent are listed in Table
11. Since it is the common fact that silica gel collection procedures always give transport efficiency with a positive bias (14), the values listed in Table I1 do not represent the true transport efficiency but they can inform about the relative difference of the efficiency on various nebulizing methods. The cross-flow nebulizer was operated at 0.45 L/min Ar gas flow rate, and water was pumped at both 16 pL/min and 4 pL/min flow rate into the system. At 16 pL/min of water flow, the efficiency values increased with the reduction of the spray chamber volume, whereas in the case of the "no-spray chamber", since aerosols stuck to the inner wall at the lower part of the sample introduction tube of the plasma torch as described above, the efficiency value seemed to decrease. In fact, some large droplets were observed on the torch wall. The efficiency value increased with the increase of the heater temperature. At 4 pL/min of the water flow, the efficiency values increased with the decrease of the spray chamber volume to 0 mL, and the values at the flow rate of 4 pL/min were superior to those a t 16 pL/min. Detector Characterization. The response of the ICP detector was characterized under optimum conditions using ethanol and ethylene glycol as model solutes and water as the mobile phase. The response of the ICP detector was linearly related to the injected solute mass from the detection limit to at least 300 pg of carbon, where the minimum detectable quantity of carbon was determined to be 100-200 ng. Therefore, the linear dynamic range was greater than lo3,and the detection limit has been improved 2 to 3 times lower than that in the previous nebulizing system (8, 9). Typical signals observed in these evaluations are shown in Figures 6 and 7, where the emission intensities of carbon at 247.86 nm are compared for ethanol and ethylene glycol under 16 pL/min and the 4 pL/min of water flow rates. In Figure 6, it appears that the signal intensity is proportional to the amount of carbon in the sample. From the results shown in Figure 7, the ICP detection system is considered to be a mass-sensitive detector, because a signal intensity is linearly dependent on the flow rate of mobile phase, water. The effects of solute structure and physical properties such as volatility on the response of the ICP were also expected to be present from the observation of the intensity difference between those of ethanol and ethylene glycol, Figure 7. To ascertain whether the chemical structure and physical properties of a solute influenced detector response, some solutes were employed to measure their signal intensity under the same experimental conditions, and those data are summarized in Table 111.
C
t
ic
E
Flgure 6. Relationship between emission signal intensity and amounts of carbon: sample, ethanol, (A) 15 pg of carbon, (B) 30 pg of carbon, (C) 60 pg of carbon (D) 120 pg of carbon.
d P f
B
J
J -
Flgure 7. Effect of water flow rate on emission signal intensity of carbon atomic line at 247.86 nm: water flow rate, (A) 4 pL/min, (E) 16 pLlmin; sample Ar gas flow rate, 0.45 L/min; sample, (A) ethylene ethanol (120 pg of carbon). glycol (120 pg of carbon), (6)
ANALYTICAL CHEMISTRY, VOL. 57, NO. 12, OCTOBER 1985
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Table 111. Emission Signal Intensity of Various Organic Compounds under the Optimized ICP Conditions“ intensity/ of carbon,
pg
compound
mm/pg
chloroform
1.45
methanol ethanol 1-propanol 2-propanol 1-butanol acetone
1.37 1.16
benzene
toluene acetic acid n-hexane cyclohexane ethyl acetate ethylene glycol
1.00
1.07 0.55 1.13 0.36 0.38 1.02 0.61 0.54 0.48 0.33
bp,
O C
61.3 64.7 78.3 97.5 82.4 117.5 56.3 80.1 110.6 117.8 68.8 80.8 76.8 197.3
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viscosity, vapor pressure, CP mmHg 0.611 1.19 2.20 2.39 2.95 0.322 1.22 0.32 0.97
(A)
160 99 120 15 33 4 175 76 21 12 120 82 74
21
C
a Sample, 0.3 p L injection; flow rate, water, 16 pL/min; sample Ar gas flow rate, 0.45 L/min.
A
Although there was no theoretically explainable difference in detector response for the solutes listed in Table 111,it seems that solutes with higher volatility have a tendency to give higher signal intensity. On that point, Novotny et al. have reported the similar observation that some discriminationdoes occur on the basis of volatility in their thermoionic detector for micro-LC (15). Therefore, it would be desirable to reoptimize plasma conditions if solutes of low volatility were to be analyzed. Performance in Use of Organic Solvents as Mobile Phase. The “no-spray chamber” nebulizing system is amenable for use in normal-phaseliquid chromatographywith pure organic solvents such as toluene and chloroform as the mobile phase. The normally difficult problems encountered in conventional HPLC-ICP when organic solvents are used as mobile phase are overcome by the use of microcolumn separations and “no-spray chamber” system. The reproducibility of emission signals in the use of “nospray chamber” nebulizing system with organic solvent as mobile phase was evaluated by the experiments, in which the injection of 0.3 KL of toluene solution of CU(DDTC)~ containing 150 ng of Cu was repeated into the Develosil column with a flow rate of 8 gL/min of toluene. The signal intensity of the Cu atomic emission line at 324.75 nm was monitored. The results indicated that the very high reproducibility of the emission signals can be obtained with the “no-spraychambern nebulizing system in microcapillary LC-ICP combination. Even if organic solvent is used as mobile phase, very stable plasma conditions are maintained due to lower flow rates of microcapillary LC. In this case, it is not required to heat up the bottom of the plasma torch which is needed in the separations with water mobile phase, because of high volatility of organic solvents. The response of the ICP for separations with organic solvents as mobile phase was estimated and the typical results are illustrated in Figure 8, in which the emission intensities of Cu a t 342.75 nm are compared under the 16 bL/min and 4 pL/min of toluene flow rates with two different sample Ar gas flow rates, Le., 0.45 L/min and 0.60 L/min, respectively. The ICP detector in these cases is also considered to be a mass-sensitive detector as the same as in the case of the water mobile phase. The linearity of the response for Cu was also observed. The detection limit of Cu is less than 1 ng and the dynamic range is greater than 103. It clearly appears that there are no restrictions found on the mobile phase characteristics, whether aqueous or organics.
Flgure 8. Effect of flow rates of sample Ar gas and mobile phase on emission signal intensity of copper at 324.75 nm: mobile phase, toluene; sample, Cu(DDTC), (150 ng of Cu); flow rate, (A) 4 pL/min, (B) 16 bL/min; Ar gas flow rate, ( A , C) 0.60 L/min, ( B , D ) 0.45 L/min. 4
t
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12
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i
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Flgure 9. Microcapillary LC-ICP chromatogram of short alkyl chain alcohols: column, 0.35 mm i.d. X 400 mm long packed with KC-811; mobile phase, water; flow rate, 4 bL/min; sample Ar gas flow rate, 0.45 L/min; heater temperature, 60 “C; peak assignments, (1) methanol, (2) ethanol, (3)2-propano1, (4) 2-methyC2-propanol, (5) 1-propanol, (6) 2-butanol, (7) 1-butanol.
Demonstration of the System. To demonstrate the potential of the ICP detector, a mixture of seven low alkyl alcohols was separated on the Shodex column. The response of the ICP monitored at 247.86 nm of carbon emission line is illustrated in Figure 9. Since a UV detector which is the most common in HPLC separations has no response for those alcohols, the potential of the ICP detection is feasible and other organic compounds which have no chromophores in their structures such as ethylene glycol and saccharides are also able
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Figure 10. Element-specific chromatograms for organometallic compounds by microcapillary LC-ICP system: column, 0.35 mm i.d. X 230 mm long packed with Develosil; mobile phase, toluene; flow rate, 4 ML/min; sample Ar gas flow rate, 0.45 L/mln; (A) UV chromatogram at 300 nm, (B) ICP chromatogram monitored at 324.75 nm for Cu, 267.72 nm for Cr, and 228.62 nm for Co.
to be monitored by the system developed in this work (7-9). The element-specific chromatograms for organometallic compounds, Cu(DDTQ2, Cr(DDTC),, and Cr(DDTC)6by the system proposed here are demonstrated in Figure 10. In this example, the specific detection for Cu, Cr, and Co has been performed by the measurementsat each element characteristic atomic emission line such as 324.75 nm for Cu, 267.72 nm for Cr, and 228.62 nm for Co, respectively. The sample amount injected into the capillary column was 50 ng of each metal element with a 0.3-pL sample introduction. It is clearly shown in this example that the microcapillary LC-ICP combination is a powerful technique for speciation of organometalliccompounds. One of the most interesting fields of practical analytical chemistry has been studies directed toward isolation and identification of organometallic compounds in various samples such as petroleum oils and biological fluids. In the majority of these studies, however, the target has been focused to independent separation, identification, and quantitation techniques (16). Therefore relatively little as yet has been done in combining both techniques to get more productive data. From this viewpoint, Fish et al. have reported the
Flgure 11. SEC chromatogram of NBS SRM-1580 shale oil: column, 0.50 mm i.d. X 600 mm long packed with TSK Gel 1000-H: mobile phase, chloroform: flow rate, 8 ML/min: (A) UV chromatogram of
polystyrene standards monltored at 254 nm (1) mol wt 900, (2) 370, (n = 3 oligomer), (3) 266 (n = 2 oligomer): (B) UV chromatogram of the shale oil monitored at 254 nm; (C) UV chromatogram of the shale oil monitored at 300 nm; (D) ICP chromatogram of the shale oil monitored at 279.55 nm of magnesium emission line; (E) ICP chromatogram of the shale oil monitored at 238.20 nm of iron emission Ilne; (F) ICP chromatogram of the shale oil monitored at 309.31 nm of vanadium emission line: (G)ICP chromatogram of the shale oil monitored at 396.15 nm of aluminum emission line. molecular characterization and profile identification of vanadyl compounds in heavy crude petroleums by LC-AAS (atomic absorption spectrometry) (17,18). Therefore it is reasonable at this time to demonstrate the potential of the microcapillary LC-ICP system for this area. A separation of a shale oil (NBS SRM-1580) was studied under the most optimized conditions, as a further demonstration of the utility of this detection system. We have used an SEC column (TSK column), which excludes compounds of molecular weight larger than 1000, because it has been reported that most interesting organometallic compounds present in petroleum samples have a molecular weight less than 900 (18). Figure 11 illustrates the SEC chromatograms of NBS SRM-1580 shale oil monitored by UV and ICP detectors, accompanied with the UV chromatogram of polystyrene standards. It appears from the chromatograms that compounds of molecular weight about a few hundred are mainly present in this shale oil, especially a sharp peak in the UV chromatograms observed around molecular weight 400 Cali-
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Anal. Chem. 1985, 57. 2235-2239
brated in terms of polystyrene. ICP element-specific detection informs us that iron- and magnesium-containing compounds distribute widely in the molecular weight range larger than 500, while vanadium-containing compounds distribute in the molecular weight range smaller than those of other metal compounds. The elution time of the sharp peak that appeared in the UV chromatograms is almost consistent with that of the vanadium peak. This result on vanadyl compounds can be explained by the fact that vanadyl porphyrin compounds have molecular weights less than 600, although complexation to the asphalthene fraction of the oil could drastically increase their apparent molecular weight (19). Even though the chromatogram monitored at aluminum emission line is not clear because of its low sensitivity, aluminum-containing compounds also seem to be present in the molecular weight range around 300. The example demonstrated here strongly implies that the microcapillary LC-ICP system can provide a molecular weight categorization of organometallic compounds present in a shale oil, although more detailed discussions on the speciation are not performed because they are beyond the scope of this contribution. With the help of this technique, speciations of organometallic compounds in petroleum samples will be attempted effectively, since the method provides information on molecular weight and spectroscopic characterization along with elemental composition. Thus it is expected to widen application especially in the fields of oil chemistry and biochemistry, as many important substances have metal atoms in their functional sites.
CONCLUSION With the direct sample introduction system, i.e., the %ospray chamber" system proposed in this work, ICP has been
able to work as a detector for microcapillary LC without any change in spectrometric characteristics. The results of this instrumental investigation show the technique will allow us more precise studies on speciation and characterization of trace metals and organometallic compounds in petroleum and biological samples.
LITERATURE CITED Lawrence, K. E.; Rice, G. W.; Fassel, V. A. Anal. Chem. 1984, 5 6 , 292. Ishii. D.; Asai, K.; Hlbl, K.; Jonokuchi, T.; Nagaya, M. J . Chromafogr. 1977, 144, 157. Novotny, M. Anal. Chem. 1981, 5 3 , 1294A. Novotny, M. Anal. Chem. 1983, 5 5 , 1308A. Jinno, K.; Tsuchlda, H. Anal. Left. 1982, 15, 427. Jinna, K.; Nakanishi, S.; Tsuchida, H.; Hlrata, Y.; Fujimoto, C. Appl. Specfrosc. 1983, 3 7 , 258. Jinno, K.; Nakanishl, S. HRC CC J . H@h Resoluf. Chromafogr. Chromafop. Commun. 1983, 6 , 210. Jinno, K.; Nakanishi, S.; Nagoshi, T. Anal. Chem. 1984, 56. 1977. Jlnno, K.; Nakanlshi, S.; Nagoshi, T. Chromatographia 1984, 18, 437. Boorn, A. W.; Browner, R. F. Anal. Chem. 1982, 5 4 , 1402. Barrett, P.; Pruszkowska,E. Anal. Chem. 1984, 56, 1927. Hausler, D. W.; Taylor, L. T. Anal. Chem. 1981, 5 3 , 1223. Schutyser, P.; Janssens, E. Spectrochlm. Acta, Part 6 1979, 346, 443. Browner, R. F.; Smlth, D. D. Anal. Chem. 1983, 5 5 , 374. McGuffin, V. L.; Novotny, M. Anal. Chem. 1983, 5 5 , 2296. Braetter, P.,Schramel, P., Eds. "Trace Element Analytical Chemistry in Medicine and Biology"; Walter de Gruyter & Co.: Berlin, 1980. Fish, R. H.; Komlenic, J. J. Anal. Chem. 1984, 5 6 , 510. Fish, R. H.; Komlenic. J. J. Anal. Chem. 1984, 5 6 , 2452. Sugihara, J. M.; Branthaver, J. F.; Wu, G. Y.; Weatherbee, C. Prepr. Am. Chem. SOC.Div. Pet. Chem. 1970, 15, C5.
RECEIVED for review March 12,1985. Accepted June 11,1985. This paper was presented in part at the 6th International Symposium on Capillary Chromatography held in Riva del Garda, Italy, in May 1985.
High-Performance Packed Glass-Lined Stainless Steel Capillary Column for Microcolumn Liquid Chromatography Masaharu Konishi,* Yoshio Mori, and Tameyuki Amano
Shionogi Research Laboratories, Shionogi & Co., Ltd., Fukushima-ku, Osaka 553, Japan
A promlslng new glass-lined stainless steel tublng was successfully used as a packed narrow-bore column for hlghperformance llquld chromatography and examlned for Its potential as a microcolumn for routlne cllnlcal work. A 30 cm X 0.3 mm column with 40000 theoretlcal plates could be easily packed with 3-pm ODS particles by the same procedure used for conventlonal columns. The analytical system used ordlnary equipment with no modlflcation except a mlniaturized flow-through cell for detection. The effect of column dimension (length and Inner diameter) on column efflclency and use of the column for routlne clinical work are dlscussed.
Recent advances in high-performance liquid chromatography (HPLC) column technology have facilitated analysis of a wide range of compounds which cannot be subjected to gas-liquid chromatography (GLC). Separation power is in-
creased by the use of high-quality microparticles for bonded phase packings (3 or 5 pm), which allow faster analysis with shorter columns. It can also be increased by capillary GLC, and some elegant attempts have been made to decrease column size by miniaturizing the system (1-5). The major benefits of microcolumn analytical technology are increased sample detectability and decreased solvent consumption. Reduction of column diameter by a factor of 10, considering the diameter to be 2-4.6 mm for a conventional column and 0.2-0.5 mm for a microcolumn, decreases solvent consumption 102-103-foldand increases detectability in a sample of limited volume. Lower flow rates offer cost savings, when expensive chemicals such as deuterated solvents and elution systems containing coenzymes (6)are employed, and also allow combination with new universal detection systems for HPLC such as flame-based photometric detection (7,8)and mass spectrometry (9,10). Capillary columns, which are generally called microcolumns, can be classified into three major categories, packed microcapillary columns (2, II), open-tubular columns
0003-2700/85/0357-2235$01.50/0 0 1965 American Chemical Society
