title: Analysis of organosilicone surfactants and their degradation products

authors: Bonnington, L. S.

abstract: In this work the analysis of the organosilicone surfactant Silwet L-77 and components thereof is described. The commercial product Silwet L-77 was demonstrated to comprise of ∼70% M₂D-C₃-O-(EO)ₙ-CH₃ (1),* ∼5% M₂D-C₃-O- (EO)ₙ-H (2) and ∼25% polar constituents. M₂D-C₃-O-(EO)ₙ-CH₃ oligomers were obtained by reversed-phase chromatography of Silwet L-77, and by synthetic procedures. Pure oligomers (n = 3, 6 and 9) were synthesised by reaction of the corresponding allyl-capped oligoethoxylate monomethyl ether M₂Dᴴ over a Pt catalyst. The allyl-capped ethoxylate monomethyl ethers were synthesised by reaction of allyl chloride with the corresponding ethoxylate monomethyl ethers (n = 3, 6 and 9). The longer chained oligoethylene glycols (n = 6 and 9) were prepared by etherification of smaller oligomers. Preparation of the organosilicone compounds M₂D-C₃-O-EO-COCH₃ and M₂D-C₃-OH were also investigated. 
Atmospheric pressure ionisation mass spectrometry (API/MS) is demonstrated to be a valid and informative method for the characterisation and quantitation of the organosilicone surfactants. Consistently reproducible quantitative results were achieved using an online HPLC separation system. Atmospheric pressure chemical ionisation (APcI) was used to enable high sample throughput, and the resulting HPLC/APcI/MS data obtained were improved both in reproducibility and sensitivity over conventional HPLC methods. 
The uptake mechanisms of agrochemical formulations and the role that surfactants play in this process are not well understood. The quantitative API/MS method developed and the use of synthesised Silwet L-77 components (1) enabled investigation of Silwet L-77 uptake into plant foliage (Chenopodium album). The influence of Silwet L-77 and constituents thereof on herbicide uptake was addressed, and dosage, spread, surfactant structure, solvation and solubility were implicated as important for uptake enhancement. 
Aspects of Silwet L-77 degradation were also addressed, for which API/MS methods were shown to be valid and informative. The well-established instability of Silwet L-77 to acid and alkaline conditions was characterised in more detail, with products, mechanisms and relative rates presented. Certain limitations of the API/MS method (i.e. product overlap, analyte suppression) required the use of additional methods to supplement the results obtained (LC/MS, GC/MS and NMR). 
The range of products formed in the degradation of Silwet L-77 were numerous as a result of the ability of the siloxane moiety to rearrange into a variety of lengths and structures, and compounded by the large number of components comprising the Silwet L-77 formulation. Unequivocal assignment of degradation product structure was thus complicated. Mass recovery following degradation was reduced in all experiments indicating the loss of volatile siloxane compounds. This was confirmed by headspace analysis. An increase in overall water-solubility for the degradation products over the parent surfactant was also observed. Rates and products appeared to be dependent on the conditions used, and were especially influenced by the solution pH. 
The use of fourier transform ion cyclotron resonance mass spectrometry (FTICR/MS) enabled the tentative assignment of four major products in the water-soluble fraction of degraded Silwet L-77. These were CH₃O(EO)ₙH (20), [1-SiCH₃+H] (21), cyclic tetramer [28; R¹, R², R³, R⁴ = C₃-O-(EO)ₙ-CH₃] and linear dimer [24; R¹, R² = TMS; R³, R⁴ = (EO)ₙ-CH₃].
Analysis of the degradation of purified M₂D-C₃-O-(EO)ₙ-Me (ave. n ∼7.5) samples by electrospray mass spectrometry (ESI/MS), FTICR/MS and HPLC/ESI/MS indicated CH₃O(EO)ₙH (20), [1-SiCH₃+H] (21) and [1- 2SiCH₃+2H] (22) as common degradation products. The linear dimer 24, [R¹ = H, R² = TMS; R³, R⁴ = (EO)ₙ-CH₃] was also indicated. The results also demonstrated that the HO(EO)ₙH, M₂D-C₃-O-(EO)n-H (2) and (Mᴿ)₂D-O-(EO)ₙ-CH₂CH= CH₂ (9, 10, 11; R = H or CH₃) compounds observed in the Silwet L-77 degradation mixture were synthetic by-products rather than degradation products. 
The degradation of single M₂D-C₃-O-(EO)ₙ-R oligomers confirmed the CH₃O(EO)ₙH (20), [1-SiCH₃+H] (21) and [1-2SiCH₃+2H] (22) as degradation products, and also indicated a range of linear and cyclic products both with and without the EO chains and terminal TMS groups intact. In general, the more silylated analogues of a structural series partitioned preferentially into the heptane-soluble fraction, and higher EO content derivatives were more commonly observed in the water-soluble fraction. Typically the products formed followed that for expected silanol stabilities, with longer EO chain products more stable as low condensation polymers and silanols, and short EO chains more commonly observed in cyclic products. 
The GC/MS analysis of the heptane-soluble fraction of acid-degraded Silwet L-77 enabled the tentative assignment of the cyclic trimer, 27 [R¹, R², R³ = -C₃- OH] product. ¹H and ¹³C NMR data also indicated this structure. ¹H NMR of the water-soluble fraction showed proton integration values indicative of the [1- 2SiCH₃+2H] (22) structure. After 2 years, the terminal Mᴿ groups were no longer detectable and extensive condensation had occurred, as determined by ²⁹Si NMR.
The results demonstrated the rapid degradation of Silwet L-77 and derivatives thereof under extremes of pH and the highly complex nature of the products which are formed. API/MS was a valid and informative method for the study of the products formed, especially the high resolution FTICR/MS technique. 
Investigation into the stability of Silwet L-77 solutions on typical soil substrates indicated that there is little chance of surfactant persistence in aqueous soil environments. Reduced recovery was considered to be a result of degradation and/or strong sorption processes. Losses were most significant on substrates exhibiting extreme supernatant pH values (montmorillonite, halloysite). Reduced recoveries were also higher with higher clay content. Studies on clays indicated that supernatant pH, potential for intercalation and surface charges are important factors in the recovery process. In the case of the montmorillonite and illite clays, recoveries may be more significantly affected by sorption, as strong surfactant substrate interactions were observed immediately following application. 
The results obtained support previous observations that Silwet L-77 is relatively benign in the natural environment. Primary degradation is rapid and ultimate degradation to naturally occurring compounds i.e. CO₂, H₂O and Si(OH)₄, can be predicted according to the structures of the observed intermediates. However covalent bonding of degradation products to substrates was observed which may result in some environmental accumulation. In land applications this could cause aggregation of silicate minerals and/or affect the sorption capacity of the soil. An increase in sorption capacity could have positive or detrimental effects. The concentrations required for biotoxicity for Silwet L-77 and degradation products thereof are in large excess of any likely input by agricultural practices. Phytotoxicity was also low and this appeared to be a result of the dilution effects caused by high spreading. 

*M₂D- [Si(CH₃)₃-O]₂-Si(CH₃)- ; C₃ = (CH₂)₃; EO = CG₂CH₂O

text: Analysis of organosilicone surfactants and their degradation products In this work the analysis of the organosilicone surfactant Silwet L-77 and components thereof is described. The commercial product Silwet L-77 was demonstrated to comprise of ∼70% M₂D-C₃-O-(EO)ₙ-CH₃ (1),* ∼5% M₂D-C₃-O- (EO)ₙ-H (2) and ∼25% polar constituents. M₂D-C₃-O-(EO)ₙ-CH₃ oligomers were obtained by reversed-phase chromatography of Silwet L-77, and by synthetic procedures. Pure oligomers (n = 3, 6 and 9) were synthesised by reaction of the corresponding allyl-capped oligoethoxylate monomethyl ether M₂Dᴴ over a Pt catalyst. The allyl-capped ethoxylate monomethyl ethers were synthesised by reaction of allyl chloride with the corresponding ethoxylate monomethyl ethers (n = 3, 6 and 9). The longer chained oligoethylene glycols (n = 6 and 9) were prepared by etherification of smaller oligomers. Preparation of the organosilicone compounds M₂D-C₃-O-EO-COCH₃ and M₂D-C₃-OH were also investigated. 
Atmospheric pressure ionisation mass spectrometry (API/MS) is demonstrated to be a valid and informative method for the characterisation and quantitation of the organosilicone surfactants. Consistently reproducible quantitative results were achieved using an online HPLC separation system. Atmospheric pressure chemical ionisation (APcI) was used to enable high sample throughput, and the resulting HPLC/APcI/MS data obtained were improved both in reproducibility and sensitivity over conventional HPLC methods. 
The uptake mechanisms of agrochemical formulations and the role that surfactants play in this process are not well understood. The quantitative API/MS method developed and the use of synthesised Silwet L-77 components (1) enabled investigation of Silwet L-77 uptake into plant foliage (Chenopodium album). The influence of Silwet L-77 and constituents thereof on herbicide uptake was addressed, and dosage, spread, surfactant structure, solvation and solubility were implicated as important for uptake enhancement. 
Aspects of Silwet L-77 degradation were also addressed, for which API/MS methods were shown to be valid and informative. The well-established instability of Silwet L-77 to acid and alkaline conditions was characterised in more detail, with products, mechanisms and relative rates presented. Certain limitations of the API/MS method (i.e. product overlap, analyte suppression) required the use of additional methods to supplement the results obtained (LC/MS, GC/MS and NMR). 
The range of products formed in the degradation of Silwet L-77 were numerous as a result of the ability of the siloxane moiety to rearrange into a variety of lengths and structures, and compounded by the large number of components comprising the Silwet L-77 formulation. Unequivocal assignment of degradation product structure was thus complicated. Mass recovery following degradation was reduced in all experiments indicating the loss of volatile siloxane compounds. This was confirmed by headspace analysis. An increase in overall water-solubility for the degradation products over the parent surfactant was also observed. Rates and products appeared to be dependent on the conditions used, and were especially influenced by the solution pH. 
The use of fourier transform ion cyclotron resonance mass spectrometry (FTICR/MS) enabled the tentative assignment of four major products in the water-soluble fraction of degraded Silwet L-77. These were CH₃O(EO)ₙH (20), [1-SiCH₃+H] (21), cyclic tetramer [28; R¹, R², R³, R⁴ = C₃-O-(EO)ₙ-CH₃] and linear dimer [24; R¹, R² = TMS; R³, R⁴ = (EO)ₙ-CH₃].
Analysis of the degradation of purified M₂D-C₃-O-(EO)ₙ-Me (ave. n ∼7.5) samples by electrospray mass spectrometry (ESI/MS), FTICR/MS and HPLC/ESI/MS indicated CH₃O(EO)ₙH (20), [1-SiCH₃+H] (21) and [1- 2SiCH₃+2H] (22) as common degradation products. The linear dimer 24, [R¹ = H, R² = TMS; R³, R⁴ = (EO)ₙ-CH₃] was also indicated. The results also demonstrated that the HO(EO)ₙH, M₂D-C₃-O-(EO)n-H (2) and (Mᴿ)₂D-O-(EO)ₙ-CH₂CH= CH₂ (9, 10, 11; R = H or CH₃) compounds observed in the Silwet L-77 degradation mixture were synthetic by-products rather than degradation products. 
The degradation of single M₂D-C₃-O-(EO)ₙ-R oligomers confirmed the CH₃O(EO)ₙH (20), [1-SiCH₃+H] (21) and [1-2SiCH₃+2H] (22) as degradation products, and also indicated a range of linear and cyclic products both with and without the EO chains and terminal TMS groups intact. In general, the more silylated analogues of a structural series partitioned preferentially into the heptane-soluble fraction, and higher EO content derivatives were more commonly observed in the water-soluble fraction. Typically the products formed followed that for expected silanol stabilities, with longer EO chain products more stable as low condensation polymers and silanols, and short EO chains more commonly observed in cyclic products. 
The GC/MS analysis of the heptane-soluble fraction of acid-degraded Silwet L-77 enabled the tentative assignment of the cyclic trimer, 27 [R¹, R², R³ = -C₃- OH] product. ¹H and ¹³C NMR data also indicated this structure. ¹H NMR of the water-soluble fraction showed proton integration values indicative of the [1- 2SiCH₃+2H] (22) structure. After 2 years, the terminal Mᴿ groups were no longer detectable and extensive condensation had occurred, as determined by ²⁹Si NMR.
The results demonstrated the rapid degradation of Silwet L-77 and derivatives thereof under extremes of pH and the highly complex nature of the products which are formed. API/MS was a valid and informative method for the study of the products formed, especially the high resolution FTICR/MS technique. 
Investigation into the stability of Silwet L-77 solutions on typical soil substrates indicated that there is little chance of surfactant persistence in aqueous soil environments. Reduced recovery was considered to be a result of degradation and/or strong sorption processes. Losses were most significant on substrates exhibiting extreme supernatant pH values (montmorillonite, halloysite). Reduced recoveries were also higher with higher clay content. Studies on clays indicated that supernatant pH, potential for intercalation and surface charges are important factors in the recovery process. In the case of the montmorillonite and illite clays, recoveries may be more significantly affected by sorption, as strong surfactant substrate interactions were observed immediately following application. 
The results obtained support previous observations that Silwet L-77 is relatively benign in the natural environment. Primary degradation is rapid and ultimate degradation to naturally occurring compounds i.e. CO₂, H₂O and Si(OH)₄, can be predicted according to the structures of the observed intermediates. However covalent bonding of degradation products to substrates was observed which may result in some environmental accumulation. In land applications this could cause aggregation of silicate minerals and/or affect the sorption capacity of the soil. An increase in sorption capacity could have positive or detrimental effects. The concentrations required for biotoxicity for Silwet L-77 and degradation products thereof are in large excess of any likely input by agricultural practices. Phytotoxicity was also low and this appeared to be a result of the dilution effects caused by high spreading. 

*M₂D- [Si(CH₃)₃-O]₂-Si(CH₃)- ; C₃ = (CH₂)₃; EO = CG₂CH₂O

year: 2000

title: An illusory size–speed bias and railway crossing collisions

authors: Isler, Robert B.

abstract: Collisions between motor vehicles and trains at railway level crossings have been a high-profile issue for many years in New Zealand and other countries. Errors made in judging a train's speed could possibly be attributed to motorists being unknowingly subjected to a size-speed illusion and this could put them at considerable risk. Leibowitz (1985) maintained that a large object seems to be moving slower than a small object travelling at the same speed. Support has been provided for Leibowitz's theory from studies using simple shapes on a screen. However, the reasons behind the size-speed illusion remain unknown and there is no experimental evidence that it applies to an approaching train situation. To investigate these issues, we tested observers' relative speed estimation performance for a train and a car approaching at a range of speeds and distances, in a simulated environment. The data show that participants significantly underestimated the speed of the train, compared to the car. A size-speed illusion seems to be operating in the case of the approaching train in our simulation and may therefore be a risk factor in some railway level crossing collisions.

text: An illusory size–speed bias and railway crossing collisions Collisions between motor vehicles and trains at railway level crossings have been a high-profile issue for many years in New Zealand and other countries. Errors made in judging a train's speed could possibly be attributed to motorists being unknowingly subjected to a size-speed illusion and this could put them at considerable risk. Leibowitz (1985) maintained that a large object seems to be moving slower than a small object travelling at the same speed. Support has been provided for Leibowitz's theory from studies using simple shapes on a screen. However, the reasons behind the size-speed illusion remain unknown and there is no experimental evidence that it applies to an approaching train situation. To investigate these issues, we tested observers' relative speed estimation performance for a train and a car approaching at a range of speeds and distances, in a simulated environment. The data show that participants significantly underestimated the speed of the train, compared to the car. A size-speed illusion seems to be operating in the case of the approaching train in our simulation and may therefore be a risk factor in some railway level crossing collisions.

year: 2013

title: The Aroha block from 1880 onwards

authors: Hart, Philip

abstract: With the discovery of gold in 1880 and the pressure to open the land for mining, there was a need to determine the boundaries of the Ngati Rahiri reserves and to subdivide these amongst the owners. As well, terms for paying goldfields revenue had to be negotiated before the goldfield could be opened, and after its opening the claims of Maori with little or no basis for their claims of ownership had to be investigated. Wairakau reserve, outside the goldfield, was not subdivided until mid-1882, and arguments over the ownership of Tui Pa continued well into the twentieth century. 
At first, sales of Crown land found few takers, especially because the farm sections required draining before they could be developed. Ngati Rahiri reserves were designated as being inalienable, but they could be leased for 21 years, as some portions were, at low rates. Very quickly, officials, who feared Maori would become landless, had to fend off requests to remove restrictions on sale made by owners who in some instances lived far from Te Aroha and who all wanted to obtain money from selling land of little use to them. The indebtedness of some owners led to continued pressure to sell, though often the money they received was wasted. With the fading of the goldfield, miners sought land for farms, and were frustrated at the Crown not purchasing the Ngati Rahiri reserves. 
Land was acquired by the Crown to extend the hot springs domain, and after negotiating improved leases in the Te Aroha township the freehold of this settlement was acquired. Some Maori retained their land, which Pakeha accused them of not improving; Maori requests that the government provide training in farming methods were ignored. By the twentieth century most Ngati Rahiri had become landless, but as many examples illustrate, this was commonly because cash-strapped owners insisted on selling their interests for an immediate financial return.

text: The Aroha block from 1880 onwards With the discovery of gold in 1880 and the pressure to open the land for mining, there was a need to determine the boundaries of the Ngati Rahiri reserves and to subdivide these amongst the owners. As well, terms for paying goldfields revenue had to be negotiated before the goldfield could be opened, and after its opening the claims of Maori with little or no basis for their claims of ownership had to be investigated. Wairakau reserve, outside the goldfield, was not subdivided until mid-1882, and arguments over the ownership of Tui Pa continued well into the twentieth century. 
At first, sales of Crown land found few takers, especially because the farm sections required draining before they could be developed. Ngati Rahiri reserves were designated as being inalienable, but they could be leased for 21 years, as some portions were, at low rates. Very quickly, officials, who feared Maori would become landless, had to fend off requests to remove restrictions on sale made by owners who in some instances lived far from Te Aroha and who all wanted to obtain money from selling land of little use to them. The indebtedness of some owners led to continued pressure to sell, though often the money they received was wasted. With the fading of the goldfield, miners sought land for farms, and were frustrated at the Crown not purchasing the Ngati Rahiri reserves. 
Land was acquired by the Crown to extend the hot springs domain, and after negotiating improved leases in the Te Aroha township the freehold of this settlement was acquired. Some Maori retained their land, which Pakeha accused them of not improving; Maori requests that the government provide training in farming methods were ignored. By the twentieth century most Ngati Rahiri had become landless, but as many examples illustrate, this was commonly because cash-strapped owners insisted on selling their interests for an immediate financial return.

year: 2016