Radial line-scans as representative sampling strategy in dried-droplet laser ablation of liquid samples deposited on pre-cut filter paper disks

Abstract

Nebulising liquid samples and using the aerosol thus obtained for further analysis is the standard method in many current analytical techniques, also with inductively coupled plasma (ICP)-based devices. With such a set-up, quantification via external calibration is usually straightforward for samples with aqueous or close-to-aqueous matrix composition. However, there is a variety of more complex samples. Such samples can be found in medical, biological, technological and industrial contexts and can range from body fluids, like blood or urine, to fuel additives or fermentation broths. Specialized nebulizer systems or careful digestion and dilution are required to tackle such demanding sample matrices. One alternative approach is to convert the liquid into a dried solid and to use laser ablation for sample introduction. Up to now, this approach required the application of internal standards or matrix-adjusted calibration due to matrix effects. In this contribution, we show a way to circumvent these matrix effects while using simple external calibration for quantification. The principle of representative sampling that we propose uses radial line-scans across the dried residue. This compensates for centro-symmetric inhomogeneities typically observed in dried spots. The effectiveness of the proposed sampling strategy is exemplified via the determination of phosphorus in biochemical fermentation media. However, the universal viability of the presented measurement protocol is postulated. Detection limits using laser ablation-ICP-optical emission spectrometry were in the order of 40 μg mL− 1 with a reproducibility of 10 % relative standard deviation (n = 4, concentration = 10 times the quantification limit). The reported sensitivity is fit-for-purpose in the biochemical context described here, but could be improved using ICP-mass spectrometry, if future analytical tasks would require it. Trueness of the proposed method was investigated by cross-validation with conventional liquid measurements, and by analyzing IAEA-153 reference material (Trace Elements in Milk Powder); a good agreement with the certified value for phosphorus was obtained.

A review on the determination of isotope ratios of boron with mass spectrometry

“…SIMS and LA‐ICPMS will continue to play a major role for in situ micro‐analysis with high spatial resolution. It will be interesting to explore the use of LA‐ICPMS for isotopic analysis and concentration of boron with dried sample solutions deposited on filter paper disks (Nischkauer et al, ) and use a radial line scan to circumvent the problem of non‐representative sampling. A combination of multiple ion counting with compact discrete dynode multipliers in MC‐ICPMS with laser ablation and ICP‐OES to simultaneously determine δ 11 B and B/Ca amount ratio reported recently sounds very promising (Kaczmarek et al, ) to analyze single foraminiferal tests.…”

The Use of Elemental Databases in Forensic Science: Studies on Vehicle Glass Interpretation and Milk Powder Provenancing

“…For the dried spot sample preparation, instead of spreading the milk solution on glass, pre-cut Whatman filter paper and plastic were used. This is a sample preparation that was used for LA-ICP-MS analysis of broth samples [41].…”

“…The third method will be referred to as the dried spot method. This sample preparation was developed by Aramendia et al and previously used by Nischkauer et al for the analysis of phosphorus in milk powder[40,41].…”

Analitikai módszerek fejlesztése folyadék és szilárd minták LIBS vizsgálatára

“…Ennek egyik hátránya, hogy a hordozó saját spektruma nagymértékben zavarhatja a minta spektrumát, ezért célszerű úgy kiválasztani a hordozót, hogy az lehetőleg ne tartalmazza a vizsgálni kívánt elemet vagy zavaró vonalakat. Egy további, nehezen kiküszöbölhető probléma a száradás során gyakran kialakuló "kávéfolt effektus", vagyis hogy a minta a folt szélén nagyobb mértékben koncentrálódik, mint a folt közepén [192]. A másik gyakori módszer a porózus szilárd hordozóval (pl.…”

“…A vizsgálatokat Cu, Ba és Al elemek vegyületeinek oldatával is elvégeztem és a kísérletek minden esetben a fenti eredményt hozták. Mindezek ellenére a kvantitatív mérés megvalósítható, mégpedig oly módon, hogy például összeintegráljuk a filter átmérője mentén mért intenzitásokat [192]. Ennél a megoldásnál nyilvánvalóan ügyelni kell arra, hogy mindig ugyanakkora legyen a hordozó átmérője, és mindig ugyanakkora lépésekkel és azonos pozíciókban vegyük fel a spektrumokat.…”