NEWS
Optimizing Instrument Parameters for High TDS
When dealing with high TDS it is recommended that the nebulizer sample flow rate is reduced as much as the required detection limits allow.
This will help prolong the lifetime of the torch by introducing less sample into the plasma. Since the injector tip is also susceptible to clogging,
utilizing a large bore injector, e.g. 2.4mm or 3.0mm, is a good idea. We also recommend increasing the auxiliary gas flow to lift the plasma
further away from the injector to help slow the build-up of salt at the injector tip. Adding a long rinse with deionized water (DIW) or very
dilute acid in between each sample of course helps the analyst to run longer without interruption and maintain optimum performance.
Utilizing the high TDS instrument parameters listed in Table 1 has allowed Inorganic Ventures to drastically reduce the amount of sample
introduced into the plasma and cut down on interrupted runs on their Spectro Arcos EOP (Axial) ICP-OES. Previously, samples with as much
as 2% TDS would deposit salt at the injector tip, resulting in poor signal stability and eventually instrument shutdown. Now, analyses involving
10,000 μg/mL and higher can be run without interruption. Although not utilized in this work, an argon humidifier, like the Capricorn can be
added to the sample introduction system. The added moisture in the gas from the humidifier helps to prevent salt build up at the nebulizer
and injector tips. This option should be explored if runs are still being interrupted after optimizing all other parameters.
Click here for more information on the Capricorn.
In addition to the changes listed in Table 1, Inorganic Ventures has also utilized a smaller i.d. peristaltic pump tubing (0.38mm), nebulizer
capillary (0.5mm), and autosampler probe (0.5mm) to reduce sample flush times. Even with sample flow rates as low as 0.24 mL/min,
the sample flush time is only 100 seconds (70 seconds at 0.6mL/min fast pump and 30 at 0.24mL/min). Another alternative is to add an
enhanced productivity accessory like the Niagara Rapid Rinse or Niagara Plus. See www.geicp.com for more information. This has been
shown to reduce rinse and stabilization times to several seconds (3).
Original Settings High TDS Settings High TDS Settings (with HF) High TDS Settings (with HF)
RF Power (W) 1400 1400 1400 1400
Plasma gas flow (L/min) 15 15 15 15
Auxiliary gas flow (L/min) 0.8 1.5 1.5 1.5
Nebulizer gas flow (L/min) 0.65 0.65 0.75 0.75
Nebulizer flow rate (mL/min) 1.2 0.24 0.54 0.54
Torch Single piece Single piece Semi-demountable Ceramic D-Torch
Injector i.d. (mm) 1.8 1.8 2.4 2.4
Nebulizer SeaSpray
(P/N ARG-07-USS2)
Spray Chamber Twister
(P/N 20-809-0243HE)
Table 1: Instrument parameters, Spectro Arcos EOP ICP-OES
SeaSpray
(P/N ARG-07-USS2)
DuraMist
(P/N ARG-07-DM1)
DuraMist
(P/N ARG-07-DM1)
Twister
(P/N 20-809-0243HE)
Tracey TFE
(P/N 20-809-2506)
Tracey TFE
(P/N 20-809-2506)
Results
Each day, Inorganic Ventures performs an ICP optimization check verifying the conditions for the ICP-OES. The data presented in Table 2
shows the optimization data collected on one day for each sample introduction setup utilized. When reducing the sample flow rate from 1.2
mL/min down to 0.24 mL/min (80% reduction) there was only a sensitivity decrease of 42% to 57%. The transport efficiency at a sample flow
rate of 0.24 mL/min is greatly improved and allows for longer runs with high TDS. The data in Table 2 also confirms that there is no significant
loss of sensitivity or increase in RSD when the introduction systems are interchanged. The “High TDS” setup uses a single piece torch with a
1.8mm i.d. injector, thus the reason for the lower counts compared to the systems utilizing a 2.4mm i.d. injector. Table 3 shows a comparison
of the fully ceramic D-Torch run at an auxiliary gas flow of 0.8 L/min versus 1.0 L/min, proving that there is no significant change in the results
when increasing the auxiliary flow to better handle high TDS.
Sample introduction system Mn 257 As 189 Pb 220
Intensity (cps) RSD (%) Intensity (cps) RSD (%) Intensity (cps) RSD (%)
Original Setup 6,126,000 ≤ 0.5 165,000 ≤ 0.5 277,000 ≤ 0.5
High TDS 3,518,000 0.35 71,226 0.83 148,760 0.30
High TDS with HF (SDT) 4,948,970 0.35 112,346 0.57 188,877 0.31
High TDS with HF (D-Torch/quartz outer tube) 5,283,250 0.27 139,672 0.51 211,841 0.28
High TDS with HF (D-Torch/ceramic outer tube) 4,679,360 0.15 105,734 0.38 170,613 0.41
* All data collected at 0.8 L/min auxiliary gas flow.
Table 2: Optimization data for each sample introduction system.
www.geicp.com Glass Expansion Newsletter | Issue 32 | page 2
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